Bash Reference Manual Reference Documentation for Bash Edition 3.1-betal, for Bash Version 3.1-betal. September 2005 Chet Ramey, Case Western Reserve University Brian Fox, Free Software Foundation EFTA00315849

This text is a brief description of the features that are present in the Bash shell (version 3.1-betal, 5 September 2005). This is Edition 3.1-betal, last updated 5 September 2005, of The GNU Bash Reference Manual, for Bash, Version 3.1-betal. Copyright @ 1988-2005 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License." (a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development." Published by the Free Software Foundation 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA EFTA00315850

Table of Contents 1 Introduction 1 1.1 What is Bash? 1 1.2 What is a shell? 1 2 Definitions 3 3 Basic Shell Features 5 3.1 Shell Syntax 5 3.1.1 Shell Operation 5 3.1.2 Quoting 5 3.1.2.1 Escape Character 6 3.1.2.2 Single Quotes 6 3.1.2.3 Double Quotes 6 3.1.2.4 ANSI-C Quoting 6 3.1.2.5 Locale-Specific Translation 7 3.1.3 Comments 7 3.2 Shell Commands 7 3.2.1 Simple Commands 8 3.2.2 Pipelines 8 3.2.3 Lists of Commands 8 3.2.4 Compound Commands 9 3.2.4.1 Looping Constructs 9 3.2.4.2 Conditional Constructs 10 3.2.4.3 Grouping Commands 13 3.3 Shell Functions 13 3.4 Shell Parameters 15 3.4.1 Positional Parameters 15 3.4.2 Special Parameters 16 3.5 Shell Expansions 17 3.5.1 Brace Expansion 17 3.5.2 Tilde Expansion 18 3.5.3 Shell Parameter Expansion 19 3.5.4 Command Substitution 21 3.5.5 Arithmetic Expansion 22 3.5.6 Process Substitution 22 3.5.7 Word Splitting 22 3.5.8 Filename Expansion 23 3.5.8.1 Pattern Matching 23 3.5.9 Quote Removal 24 3.6 Redirections 24 3.6.1 Redirecting Input 25 3.6.2 Redirecting Output 26 EFTA00315851

ii Bash Reference Manual 3.6.3 Appending Redirected Output 26 3.6.4 Redirecting Standard Output and Standard Error 26 3.6.5 Here Documents 26 3.6.6 Here Strings 27 3.6.7 Duplicating File Descriptors 27 3.6.8 Moving File Descriptors 27 3.6.9 Opening File Descriptors for Reading and Writing 28 3.7 Executing Commands 28 3.7.1 Simple Command Expansion 28 3.7.2 Command Search and Execution 29 3.7.3 Command Execution Environment 29 3.7.4 Environment 30 3.7.5 Exit Status 31 3.7.6 Signals 31 3.8 Shell Scripts 32 4 Shell Builtin Commands 33 4.1 Bourne Shell Builtins 33 4.2 Bash Builtin Commands 39 4.3 The Set Builtin 50 4.4 Special Builtins 54 5 Shell Variables 55 5.1 Bourne Shell Variables 55 5.2 Bash Variables 55 6 Bash Features 65 6.1 Invoking Bash 65 6.2 Bash Startup Files 67 6.3 Interactive Shells 69 6.3.1 What is an Interactive Shell? 69 6.3.2 Is this Shell Interactive 69 6.3.3 Interactive Shell Behavior 69 6.4 Bash Conditional Expressions 70 6.5 Shell Arithmetic 72 6.6 Aliases 73 6.7 Arrays 74 6.8 The Directory Stack 75 6.8.1 Directory Stack Builtins 75 6.9 Controlling the Prompt 76 6.10 The Restricted Shell 78 6.11 Bash POSIX Mode 78 EFTA00315852

7 8 Job Control 7.1 Job Control Basics 7.2 Job Control Builtins 7.3 Job Control Variables Command Line Editing 83 83 84 85 87 8.1 Introduction to Line Editing 87 8.2 Readline Interaction 87 8.2.1 Readline Bare Essentials 87 8.2.2 Readline Movement Commands 88 8.2.3 Readline Killing Commands 88 8.2.4 Readline Arguments 89 8.2.5 Searching for Commands in the History 89 8.3 Readline Init File 90 8.3.1 Readline Init File Syntax 90 8.3.2 Conditional Init Constructs 95 8.3.3 Sample Init File 96 8.4 Bindable Readline Commands 99 8.4.1 Commands For Moving 99 8.4.2 Commands For Manipulating The History 99 8.4.3 Commands For Changing Text 101 8.4.4 Killing And Yanking 102 8.4.5 Specifying Numeric Arguments 103 8.4.6 Letting Readline Type For You 103 8.4.7 Keyboard Macros 104 8.4.8 Some Miscellaneous Commands 105 8.5 Readline vi Mode 107 8.6 Programmable Completion 107 8.7 Programmable Completion Builtins 109 9 Using History Interactively 113 9.1 Bash History Facilities 113 9.2 Bash History Builtins 113 9.3 History Expansion 115 9.3.1 Event Designators 115 9.3.2 Word Designators 116 9.3.3 Modifiers 117 10 Installing Bash 119 10.1 Basic Installation 119 10.2 Compilers and Options 119 10.3 Compiling For Multiple Architectures 120 10.4 Installation Names 120 10.5 Specifying the System Type 120 10.6 Sharing Defaults 121 10.7 Operation Controls 121 10.8 Optional Features 121 iii EFTA00315853

iv Bash Reference Manual Appendix A Reporting Bugs 127 Appendix B Major Differences From The Bourne Shell 129 B.1 Implementation Differences From The SVR4.2 Shell 133 Appendix C Copying This Manual C.1 GNU Free Documentation License C.1.1 ADDENDUM: How to use this License for your documents 135 135 141 Index of Shell Builtin Commands 143 Index of Shell Reserved Words 145 Parameter and Variable Index 147 Function Index 149 Concept Index 151 EFTA00315854

Chapter 1: Introduction 1 Introduction 1.1 What is Bash? 1 Bash is the shell, or command language interpreter, for the GNU operating system. The name is an acronym for the `Bourne-Again Shell', a pun on Stephen Bourne, the author of the direct ancestor of the current Unix shell ah, which appeared in the Seventh Edition Bell Labs Research version of Unix. Bash is largely compatible with ah and incorporates useful features from the Korn shell kah and the C shell csh. It is intended to be a conformant implementation of the IEEE POSIX Shell and Tools specification (IEEE Working Group 1003.2). It offers functional improvements over sh for both interactive and programming use. While the GNU operating system provides other shells, including a version of esh, Bash is the default shell. Like other GNU software, Bash is quite portable. It currently runs on nearly every version of Unix and a few other operating systems — independently-supported ports exist for MS-DOS, OS/2, and Windows platforms. 1.2 What is a shell? At its base, a shell is simply a macro processor that executes commands. The term macro processor means functionality where text and symbols are expanded to create larger expressions. A Unix shell is both a conunand interpreter and a programming language. As a com- mand interpreter, the shell provides the user interface to the rich set of GNU utilities. The programming language features allow these utilitites to be combined. Files containing com- mands can be created, and become commands themselves. These new commands have the same status as system commands in directories such as 4/ bin', allowing users or groups to establish custom environments to automate their common tasks. Shells may be used interactively or non-interactively. In interactive mode, they accept input typed front the keyboard. When executing non-interactively, shells execute commands read from a file. A shell allows execution of GNU commands, both synchronously and asynchronously. The shell waits for synchronous commands to complete before accepting more input; asyn- chronous commands continue to execute in parallel with the shell while it reads and executes additional commands. The redirection constructs permit fine-grained control of the input and output of those commands. Moreover, the shell allows control over the contents of commands' environments. Shells also provide a small set of built-in commands (builtins) implementing function- ality impossible or inconvenient to obtain via separate utilities. For example, cd, break, continue, and exec) cannot be implemented outside of the shell because they directly manipulate the shell itself. The history, getopts, kill, or pwd builtins, among others, could be implemented in separate utilities, but they are more convenient to use as builtin commands. All of the shell builtins are described in subsequent sections. EFTA00315855

2 Bash Reference Manual While executing commands is essential, most of the power (and complexity) of shells is due to their embedded programming languages. Like any high-level language, the shell provides variables, flow control constructs, quoting, and functions. Shells offer features geared specifically for interactive use rather than to augment the pro- gramming language. These interactive features include job control, command line editing, command history and aliases. Each of these features is described in this manual. EFTA00315856

Chapter 2: Definitions 3 2 Definitions These definitions are used throughout the remainder of this manual. POSIX A family of open system standards based on Unix. Bash is concerned with POSIX 1003.2, the Shell and Tools Standard. blank A space or tab character. built in A command that is implemented internally by the shell itself, rather than by an executable program somewhere in the file system. control operator A word that performs a control function. It is a newline or one of the following: I 11, le , le, `;', C; ; C, or T. exit status The value returned by a command to its caller. The value is restricted to eight bits, so the maximum value is 255. field A unit of text that is the result of one of the shell expansions. After expansion, when executing a command, the resulting fields are used as the command name and arguments. filename A string of characters used to identify a file. j ob A set of processes comprising a pipeline, and any processes descended from it, that are all in the same process group. job control A mechanism by which users can selectively stop (suspend) and restart (resume) execution of processes. metacharacter A character that, when unquoted, separates words. A metacharacter is a blank or one of the following characters: ' I ', `;', C, `<', or `>'. name A word consisting solely of letters, numbers, and underscores, and beginning with a letter or underscore. Names are used as shell variable and function names. Also referred to as an identifier. operator A control operator or a redirection operator. See Section 3.6 [B,edirec- tions], page 25, for a list of redirection operators. process group A collection of related processes each having the same process group ID. process group ID A unique identifer that represents a process group during its lifetime. reserved word A word that has a special meaning to the shell. Most reserved words introduce shell flow control constructs, such as for and while. return status A synonym for exit status. EFTA00315857

4 Bash Reference Manual signal A mechanism by which a process may be notified by the kernel of an event occurring in the system. special builtin A shell builtin command that has been classified as special by the POSIX 1003.2 standard. token A sequence of characters considered a single unit by the shell. It is either a word or an operator. word A token that is not an operator. EFTA00315858

Chapter 3: Basic Shell Features 5 3 Basic Shell Features Bash is an acronym for 'Bourne-Again SHell'. The Bourne shell is the traditional Unix shell originally written by Stephen Bourne. All of the Bourne shell builtin commands are available in Bash, The rules for evaluation and quoting are taken from the POSIX specifica- tion for the `standard' Unix shell. This chapter briefly summarizes the shell's 'building blocks': commands, control struc- tures, shell functions, shell parameters, shell expansions, redirections, which are a way to direct input and output from and to named files, and how the shell executes commands. 3.1 Shell Syntax When the shell reads input, it proceeds through a sequence of operations. If the input indicates the beginning of a continent, the shell ignores the continent symbol (`ir), and the rest of that line. Otherwise, roughly speaking, the shell reads its input and divides the input into words and operators, employing the quoting rules to select which meanings to assign various words and characters. The shell then parses these tokens into commands and other constructs, removes the special meaning of certain words or characters, expands others, redirects input and output as needed, executes the specified command, waits for the command's exit status, and makes that exit status available for further inspection or processing. 3.1.1 Shell Operation The following is a brief description of the shell's operation when it reads and executes a command. Basically, the shell does the following: 1. Reads its input from a file (see Section 3.8 [Shell Scripts], page 32), from a string supplied as an argument to the `-c' invocation option (see Section 6.1 [Invoking Bash], page 65), or from the user's terminal. 2. Breaks the input into words and operators, obeying the quoting rules described in Section 3.1.2 [Quoting], page 6. These tokens are separated by metacharacters. Alias expansion is performed by this step (see Section 6.6 [Aliases], page 73). 3. Parses the tokens into simple and compound commands (see Section 3.2 [Shell Com- mands], page 8). 4. Performs the various shell expansions (see Section 3.5 [Shell Expansions], page 17), breaking the expanded tokens into lists of filenames (see Section 3.5.8 [Filename Ex- pansion], page 23) and conunands and arguments. 5. Performs any necessary redirections (see Section 3.6 [Redirection], page 25) and re- moves the redirection operators and their operands from the argument list. 6. Executes the command (see Section 3.7 [Executing Commands], page 28). 7. Optionally waits for the command to complete and collects its exit status (see Sec- tion 3.7.5 [Exit Status], page 31). EFTA00315859

6 Bash Reference Manual 3.1.2 Quoting Quoting is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable special treatment for special characters, to prevent reserved words from being recognized as such, and to prevent parameter expansion. Each of the shell metacharacters (see Chapter 2 [Definitions], page 3) has special meaning to the shell and must be quoted if it is to represent itself. When the command history expansion facilities are being used (see Section 9.3 [History Interaction], page 115), the history expansion character, usually '!', must be quoted to prevent history expansion. See Section 9.1 [Bash History Facilities], page 113, for more details concerning history expansion. There are three quoting mechanisms: the escape character, single quotes, and double quotes. 3.1.2.1 Escape Character A non-quoted backslash `\' is the Bash escape character. It preserves the literal value of the next character that follows, with the exception of newline. If a \newline pair appears, and the backslash itself is not quoted, the \newline is treated as a line continuation (that is, it is removed from the input stream and effectively ignored). 3.1.2.2 Single Quotes Enclosing characters in single quotes (" ') preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash. 3.1.2.3 Double Quotes Enclosing characters in double quotes Cul preserves the literal value of all characters within the quotes, with the exception of '$', " '\', and, when history expansion is enabled, '!'. The characters '5' and "' retain their special meaning within double quotes (see Sec- tion 3.5 [Shell Expansions], page 17). The backslash retains its special meaning only when followed by one of the following characters: `5', "', "", '\', or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ! ' appearing in double quotes is escaped using a backslash. The backslash preceding the '!' is not removed. The special parameters '*' and have special meaning when in double quotes (see Section 3.5.3 [Shell Parameter Expansion], page 19). 3.1.2.4 ANSI-C Quoting Words of the form $ ' string are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows: EFTA00315860

Chapter 3: Basic Shell Features 7 \a alert (bell) \b backspace \e an escape character (not ANSI C) \f form feed \n newline \r carriage return \t horizontal tab \v vertical tab \\ backslash single quote \nnn the eight-bit character whose value is the octal value nnn (one to three digits) \ xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits) \ cx a control-x character The expanded result is single-quoted, as if the dollar sign had not been present. 3.1.2.5 Locale-Specific Translation A double-quoted string preceded by a dollar sign (I') will cause the string to be trans- lated according to the current locale. If the current locale is C or POSIX, the dollar sign is ignored. If the string is translated and replaced, the replacement is double-quoted. Some systems use the message catalog selected by the LC_MESSAGES shell variable. Others create the name of the message catalog from the value of the TEXTDOMAIN shell variable, possibly adding a suffix of ' .mo'. If you use the TEXTDOMAIN variable, you may need to set the TEXTDOMAINDIR variable to the location of the message catalog files. Still others use both variables in this fashion: TEXTDOMAINDIR/LC_MESSAGES/LC_IvIESSAGES/TEXTDOMAIN.mo. 3.1.3 Comments In a non-interactive shell, or an interactive shell in which the interactive_comments option to the shopt builtin is enabled (see Section 4.2 [Bash Builtins], page 39), a word beginning with causes that word and all remaining characters on that line to be ignored. An interactive shell without the interactive_comments option enabled does not allow comments. The interactive_comments option is on by default in interactive shells. See Section 6.3 [Interactive Shells], page 69, for a description of what makes a shell interactive. EFTA00315861

8 Bash Reference Manual 3.2 Shell Commands A simple shell command such as echo a b e consists of the command itself followed by arguments, separated by spaces. More complex shell commands are composed of simple commands arranged together in a variety of ways: in a pipeline in which the output of one command becomes the input of a second, in a loop or conditional construct, or in some other grouping. 3.2.1 Simple Commands A simple command is the kind of command encountered most often. It's just a sequence of words separated by blanks, terminated by one of the shell's control operators (see Chap- ter 2 ['Definitions], page 3). The first word generally specifies a command to be executed, with the rest of the words being that command's arguments. The return status (see Section 3.7.5 [Exit Status], page 31) of a simple command is its exit status as provided by the POSIX 1003.1 waitpid function, or 128+n if the command was terminated by signal n. 3.2.2 Pipelines A pipeline is a sequence of simple commands separated by ' '. The format for a pipeline is [time [-p]] 1!) command.' CI command2 .. .] The output of each command in the pipeline is connected via a pipe to the input of the next command. That is, each command reads the previous command's output. The reserved word time causes timing statistics to be printed for the pipeline once it finishes. The statistics currently consist of elapsed (wall-clock) time and user and system time consumed by the command's execution. The `-p' option changes the output format to that specified by POSIX. The TIMEFORMAT variable may be set to a format string that specifies how the timing information should be displayed. See Section 5.2 [Bash Variables], page 55, for a description of the available formats. The use of time as a reserved word per- mits the timing of shell builtins, shell functions, and pipelines. An external time command cannot time these easily. If the pipeline is not executed asynchronously (see Section 3.2.3 [Lists], page 9), the shell waits for all commands in the pipeline to complete. Each command in a pipeline is executed in its own subshell (see Section 3.7.3 [Command Execution Environment], page 29). The exit status of a pipeline is the exit status of the last command in the pipeline, unless the pipefail option is enabled (see Section 4.3 (The Set Builtin], page 51). If pipefail is enabled, the pipeline's return status is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands exit successfully. If the reserved word `!' precedes the pipeline, the exit status is the logical negation of the exit status as described above. The shell waits for all commands in the pipeline to terminate before returning a value. EFTA00315862

Chapter 3: Basic Shell Features 9 3.2.3 Lists of Commands A list is a sequence of one or more pipelines separated by one of the operators '; le, or ' I I', and optionally terminated by one of ';', 1', or a newline. Of these list operators, '&&' and'I I' have equal precedence, followed by 4; ' and which have equal precedence. A sequence of one or more newlines may appear in a list to delimit commands, equiv- alent to a semicolon. If a command is terminated by the control operator the shell executes the command asynchronously in a subshell. This is known as executing the command in the background. The shell does not wait for the command to finish, and the return status is 0 (true). When job control is not active (see Chapter 7 [Job Control], page 83), the standard input for asynchronous commands, in the absence of any explicit redirections, is redirected from /dev/null. Commands separated by a '; ' are executed sequentially; the shell waits for each conunand to terminate in turn. The return status is the exit status of the last command executed. The control operators Ite and ' I I' denote AND lists and OR lists, respectively. An AND list has the form commandl && command2 command2 is executed if, and only if, command! returns an exit status of zero. An OR list has the form commandl I I command2 command2 is executed if, and only if, commandl returns a non-zero exit status. The return status of AND and OR lists is the exit status of the last command executed in the list. 3.2.4 Compound Commands Compound conunands are the shell programming constructs. Each construct begins with a reserved word or control operator and is terminated by a corresponding reserved word or operator. Any redirections (see Section 3.6 [Redirection], page 25) associated with a compound command apply to all commands within that compound command unless explicitly overridden. Bash provides looping constructs, conditional conunands, and mechanisms to group commands and execute them as a unit. 3.2.4.1 Looping Constructs Bash supports the following looping constructs. Note that wherever a '; ' appears in the description of a command's syntax, it may be replaced with one or more newlines. until The syntax of the until command is: EFTA00315863

10 Bash Reference Manual until test-commands; do consequent-commands; done Execute consequent-commands as long as test-commands has an exit status which is not zero. The return status is the exit status of the last command executed in consequent-commands, or zero if none was executed. while The syntax of the while command is: while test-commands; do consequent-commands; done Execute consequent-commands as long as test-commands has an exit status of zero. The return status is the exit status of the last command executed in consequent-commands, or zero if none was executed. for The syntax of the for command is: for name [in words . .] ; do commands; done Expand words, and execute commands once for each member in the resultant list, with name bound to the current member. If 'in words' is not present, the for command executes the commands once for each positional parameter that is set, as if `in "VP' had been specified (see Section 3.4.2 [Special Parameters], page 16). The return status is the exit status of the last command that executes. If there are no items in the expansion of words, no commands are executed, and the return status is zero. An alternate form of the for command is also supported: for (( exprl ; expr2 ; expr3 )) ; do commands ; done First, the arithmetic expression exprl is evaluated according to the rules de- scribed below (see Section 6.5 [Shell Arithmetic], page 72). The arithmetic expression expr2 is then evaluated repeatedly until it evaluates to zero. Each time expr2 evaluates to a non-zero value, commands are executed and the arith- metic expression expr3 is evaluated. If any expression is omitted, it behaves as if it evaluates to 1. The return value is the exit status of the last command in list that is executed, or false if any of the expressions is invalid. The break and continue builtins (see Section 4.1 [Bourne Shell Builtins], page 33) may be used to control loop execution. 3.2.4.2 Conditional Constructs if The syntax of the if command is: if test-commands; then consequent-commands; [elif more-test-commands; then more-consequents ;) [else alternate-consequents ;] fi The test-commands list is executed, and if its return status is zero, the consequent-commands list is executed. If test-commands returns a non-zero status, each elif list is executed in turn, and if its exit status is zero, the corresponding more-consequents is executed and the command completes. If EFTA00315864

Chapter 3: Basic Shell Features 11 'else alternate -consequents' is present, and the final command in the final if or elif clause has a non-zero exit status, then alternate-consequents is executed. The return status is the exit status of the last command executed, or zero if no condition tested true. Case The syntax of the case command is: case word in [0 pattern [I pattern] . ..) command-list ; ;] esac case will selectively execute the command-list corresponding to the first pat- tern that matches word. If the shell option nocasematch (see the description of shopt in Section 4.2 [Bash Builtins], page 39) is enabled, the match is per- formed without regard to the case of alphabetic characters. The ' I ' is used to separate multiple patterns, and the ')' operator terminates a pattern list. A list of patterns and an associated command-list is known as a clause. Each clause must be terminated with '; ;'. The word undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal be- fore matching is attempted. Each pattern undergoes tilde expansion, parameter expansion, command substitution, and arithmetic expansion. There may be an arbitrary number of case clauses, each terminated by a '; ; The first pattern that matches determines the command-list that is executed. Here is an example using case in a script that could be used to describe one interesting feature of an animal: echo -n "Enter the name of an animal: read ANIMAL echo -n "The $ANIMAL has " case $ANIMAL in horse I dog I cat) echo -n "four";; man I kangaroo ) echo -n "two";; *) echo -n "an unknown number of";; esac echo " legs." The return status is zero if no pattern is matched. Otherwise, the return status is the exit status of the command-list executed. select The select construct allows the easy generation of menus. It has almost the same syntax as the for command: select name [in words .] ; do commands; done The list of words following in is expanded, generating a list of items. The set of expanded words is printed on the standard error output stream, each preceded by a munber. If the 'in words' is omitted, the positional parameters are printed, as if 'in "$($"' had been specifed. The PS3 prompt is then displayed and a line is read from the standard input. If the line consists of a number corresponding to one of the displayed words, then the value of name is set to that word. If the line is empty, the words and prompt are displayed again. If EOF is read, the select command completes. Any other value read causes name to be set to null. The line read is saved in the variable REPLY. EFTA00315865

12 Bash Reference Manual The commands are executed after each selection until a break command is executed, at which point the select command completes. Here is an example that allows the user to pick a filename from the current directory, and displays the name and index of the file selected. select fname in *; do echo you picked $f name \($REPLY\) break; done (( expression )) The arithmetic expression is evaluated according to the rules described below (see Section 6.5 [Shell Arithmetic], page 72). If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to let "expression" See Section 4.2 [Bash Builtins], page 39, for a full description of the let builtin. (C expression ]] Return a status of 0 or 1 depending on the evaluation of the conditional expres- sion expression. Expressions are composed of the primaries described below in Section 6.4 [Bash Conditional Expressions], page 71. Word splitting and file- name expansion are not performed on the words between the ' L' and 1 '; tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process substitution, and quote removal are performed. Condi- tional operators such as `-f' must be =quoted to be recognized as primaries. When the `==' and ' = operators are used, the string to the right of the operator is considered a pattern and matched according to the niles described below in Section 3.5.8.1 [Pattern Matching], page 23. If the shell option nocasematch (see the description of shopt in Section 4.2 [Bash Builtins], page 39) is enabled, the match is performed without regard to the case of alphabetic characters. The return value is 0 if the string matches or does not match the pattern, respectively, and 1 otherwise. Any part of the pattern may be quoted to force it to be matched as a string. An additional binary operator, `=', is available, with the same precedence as `==' and `!=. When it is used, the string to the right of the operator is consid- ered an extended regular expression and matched accordingly (as in regex3)). The return value is 0 if the string matches the pattern, and 1 otherwise. If the regular expression is syntactically incorrect, the conditional expression's re- turn value is 2. If the shell option nocasematch (see the description of shopt in Section 4.2 [Bash Builtins], page 39) is enabled, the match is performed without regard to the case of alphabetic characters. Substrings matched by parenthesized subexpressions within the regular expression are saved in the array variable BASH_REMATCH. The element of BASH_REMATCH with index 0 is EFTA00315866

Chapter 3: Basic Shell Features 13 the portion of the string matching the entire regular expression. The element of BASH_REMATCH with index n is the portion of the string matching the nth parenthesized subexpression. Expressions may be combined using the following operators, listed in decreasing order of precedence: ( expression ) Returns the value of expression. This may be used to override the normal precedence of operators. ! expression True if expression is false. expression! tat expression2 'flue if both expression.? and expression2 are true. expression! I I expression2 True if either expression.' or expression2 is true. The a and I I operators do not evaluate expression2 if the value of exprassionl is sufficient to determine the return value of the entire conditional expression. 3.2.4.3 Grouping Commands Bash provides two ways to group a list of commands to be executed as a unit. When com- mands are grouped, redirections may be applied to the entire command list. For example, the output of all the commands in the list may be redirected to a single stream. 0 ( list ) Placing a list of commands between parentheses causes a subshell environment to be created (see Section 3.7.3 (Command Execution Environment], page 29), and each of the commands in list to be executed in that subshell. Since the list is executed in a subshell, variable assignments do not remain in effect after the subshell completes. {} { list; } Placing a list of commands between curly braces causes the list to be executed in the current shell context. No subshell is created. The semicolon (or 'towline) following list is required. In addition to the creation of a subshell, there is a subtle difference between these two constructs due to historical reasons. The braces are reserved words, so they must be separated from the list by blanks. The parentheses are operators, and are recognized as separate tokens by the shell even if they are not separated from the list by whitespace. The exit status of both of these constructs is the exit status of list. EFTA00315867

14 Bash Reference Manual 3.3 Shell Functions Shell functions are a way to group commands for later execution using a single name for the group. They are executed just like a "regular" command. When the name of a shell function is used as a simple command name, the list of commands associated with that function name is executed. Shell functions are executed in the current shell context; no new process is created to interpret them. Functions are declared using this syntax: [ function ] name () compound-command [ redirection ] This defines a shell function named name. The reserved word function is optional. If the function reserved word is supplied, the parentheses are optional. The body of the function is the compound command compound-command (see Section 3.2.4 [Compound Commands], page 9). That command is usually a list enclosed between { and }, but may be any compound conunand listed above. compound-command is executed whenever name is specified as the name of a command. Any redirections (see Section 3.6 [Redirection* page 25) associated with the shell function are performed when the function is executed. The exit status of a function definition is zero unless a syntax error occurs or a readonly function with the same name already exists. When executed, the exit status of a function is the exit status of the last command executed in the body. Note that for historical reasons, in the most common usage the curly braces that surround the body of the function must be separated from the body by blanks or newlines. This is because the braces are reserved words and are only recognized as such when they are separated by whitespace. Also, when using the braces, the list must be terminated by a semicolon, a `✓e, or a newline. When a function is executed, the arguments to the function become the positional pa- rameters during its execution (see Section 3.4.1 [Positional Parameters], page 15). The special parameter It' that expands to the number of positional parameters is updated to reflect the change. Special parameter 0 is unchanged. The first element of the FUNCNAME variable is set to the name of the function while the function is executing. All other aspects of the shell execution environment are identical between a function and its caller with the exception that the DEBUG and RETURN traps are not inherited unless the function has been given the trace attribute using the declare builtin or the -o functrace option has been enabled with the set builtin, (in which case all functions inherit the DEBUG and RETURN traps). See Section 4.1 [Bourne Shell Builtins], page 33, for the description of the trap builtin. If the builtin command return is executed in a function, the function completes and execution resumes with the next command after the function call. Any command associated with the RETURN trap is executed before execution resumes. When a function completes, the values of the positional parameters and the special parameter `tt' are restored to the values they had prior to the function's execution. If a numeric argument is given to return, that is the function's return status; otherwise the function's return status is the exit status of the last command executed before the return. Variables local to the function may be declared with the local builtin. These variables are visible only to the function and the commands it invokes. EFTA00315868

Chapter 3: Basic Shell Features 15 Function names and definitions may be listed with the `-f' option to the declare or typeset builtin commands (see Section 4.2 [Bash Builtins], page 39). The `-F' option to declare or typeset will list the function names only (and optionally the source file and line number, if the extdebug shell option is enabled). Functions may be exported so that subshells automatically have them defined with the `-f' option to the export builtin (see Section 4.1 [Bourne Shell Builtins], page 33). Note that shell functions and variables with the same name may result in multiple identically-named entries in the environment passed to the shell's children. Care should be taken in cases where this may cause a problem. Functions may be recursive. No limit is placed on the number of recursive calls. 3.4 Shell Parameters A parameter is an entity that stores values. It can be a name, a number, or one of the special characters listed below. A variable is a parameter denoted by a name. A variable has a value and zero or more attributes. Attributes are assigned using the declare builtin command (see the description of the declare builtin in Section 4.2 [Bash Builtins], page 39). A parameter is set if it has been assigned a value. The null string is a valid value. Once a variable is set, it may be unset only by using the unset builtin command. A variable may be assigned to by a statement of the form name=(value] If value is not given, the variable is assigned the null string. All values undergo tilde ex- pansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal (detailed below). If the variable has its integer attribute set, then value is evaluated as an arithmetic expression even if the $ ((...)) expansion is not used (see Section 3.5.5 [Arithmetic Expansion], page 22). Word splitting is not performed, with the exception of "$C" as explained below. Filename expansion is not performed. Assign- ment statements may also appear as arguments to the alias, declare, typeset, export, readonly, and local builtin commands. In the context where an assignment statement is assigning a value to a shell variable or array index (see Section 6.7 [Arrays], page 74), the `+=' operator can be used to append to or add to the variable's previous value. When `+=' is applied to a variable for which the integer attribute has been set, value is evaluated as an arithmetic expression and added to the variable's current value, which is also evaluated. When 'I.& is applied to an array variable using compound assignment (see Section 6.7 [Arrays], page 74), the variable's value is not unset (as it is when using ='), and new values are appended to the array beginning at one greater than the array's maximum index. When applied to a string-valued variable, value is expanded and appended to the variable's value. 3.4.1 Positional Parameters A positional parameter is a parameter denoted by one or more digits, other than the single digit 0. Positional parameters are assigned from the shell's arguments when it is invoked, and may be reassigned using the set builtin command. Positional parameter N may be referenced as ${N}, or as $N when N consists of a single digit. Positional parameters may not be assigned to with assignment statements. The set and shift builtins are used EFTA00315869

16 Bash Reference Manual to set and unset them (see Chapter 4 [Shell Builtin Commands], page 33). The positional parameters are temporarily replaced when a shell function is executed (see Section 3.3 [Shell Functions], page 14). When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces. 3.4.2 Special Parameters The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. ■ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the IFS special variable. That is, "$•" is equivalent to "$1 c$2c ", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are separated by spaces. If IFS is null, the parameters are joined without intervening separators. 0 Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$0" is equivalent to "$1" "$2" .... If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. When there are no positional parameters, "SC" and $0 expand to nothing (i.e., they are removed). Expands to the number of positional parameters in decimal. Expands to the exit status of the most recently executed foreground pipeline. 0 (A hyphen.) Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the `-i.' option). Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the invoking shell, not the subshell. Expands to the process ID of the most recently executed background (asyn- chronous) command. Expands to the name of the shell or shell script. This is set at shell initialization. If Bash is invoked with a file of commands (see Section 3.8 [Shell Scripts], page 32), $0 is set to the name of that file. If Bash is started with the `-c' option (see Section 6.1 [Invoking Bash], page 65), then $0 is set to the first argument after the string to be executed, if one is present. Otherwise, it is set to the filename used to invoke Bash, as given by argument zero. (An underscore.) At shell startup, set to the absolute pathname used to invoke the shell or shell script being executed as passed in the environment or argument list. Subsequently, expands to the last argument to the previous command, after expansion. Also set to the full pathname used to invoke each command EFTA00315870

Chapter 3: Basic Shell Features 17 executed and placed in the environment exported to that command. When checking mail, this parameter holds the name of the mail file. 3.5 Shell Expansions Expansion is performed on the command line after it has been split into tokens. There are seven kinds of expansion performed: • brace expansion • tilde expansion • parameter and variable expansion • command substitution • arithmetic expansion • word splitting • filename expansion The order of expansions is: brace expansion, tilde expansion, parameter, variable, and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and filename expansion. On systems that can support it, there is an additional expansion available: process substitution. This is performed at the same time as parameter, variable, and arithmetic expansion and command substitution. Only brace expansion, word splitting, and filename expansion can change the number of words of the expansion; other expansions expand a single word to a single word. The only exceptions to this are the expansions of "Se" (see Section 3.4.2 [Special Parameters], page 16) and "VnameMI" (see Section 6.7 [Arrays], page 74). After all expansions, quote removal (see Section 3.5.9 [Quote Removal], page 24) is performed. 3.5.1 Brace Expansion Brace expansion is a mechanism by which arbitrary strings may be generated. This mech- anism is similar to filename expansion (see Section 3.5.8 [Filename Expansion], page 23), but the file names generated need not exist. Patterns to be brace expanded take the form of an optional preamble, followed by either a series of comma-separated strings or a sequnce expression between a pair of braces, followed by an optional postscript. The preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string, expanding left to right. Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example, baah$ echo a-RI, c,ble ade ace abe A sequence expression takes the form {x. . y}, where x and y are either integers or single characters. When integers are supplied, the expression expands to each number between x and y, inclusive. When characters are supplied, the expression expands to each character EFTA00315871

18 Bash Reference Manual lexicographically between x and y, inclusive. Note that both x and y must be of the same type. Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result. It is strictly textual. Bash does not apply any syntactic interpretation to the context of the expansion or the text between the braces. To avoid conflicts with parameter expansion, the string 1{' is not considered eligible for brace expansion. A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma or a valid sequence expression. Any incorrectly formed brace expansion is left unchanged. A { or may be quoted with a backslash to prevent its being considered part of a brace expression. lb avoid conflicts with parameter expansion, the string 1{' is not considered eligible for brace expansion. This construct is typically used as shorthand when the common prefix of the strings to be generated is longer than in the above example: mkdir /usr/local/src/bash/{old,new,dist ,bugs} chows root /usr/fucb/{ex,edit},libi{ex?.?*,liow_ex}} 3.5.2 Tilde Expansion or If a word begins with an unquoted tilde character ('), all of the characters up to the first unquoted slash (or all characters, if there is no unquoted slash) are considered a tilde-prefix. If none of the characters in the tilde-prefix are quoted, the characters in the tilde-prefix following the tilde are treated as a possible login name. If this login name is the null string, the tilde is replaced with the value of the HOME shell variable. If HOME is onset, the home directory of the user executing the shell is substituted instead. Otherwise, the tilde-prefix is replaced with the home directory associated with the specified login name. If the tilde-prefix is `+', the value of the shell variable PWD replaces the tilde-prefix. If the tilde-prefix is 4"-', the value of the shell variable OLDPWD, if it is set, is substituted. If the characters following the tilde in the tilde-prefix consist of a number N, optionally prefixed by a `+' or a the tilde-prefix is replaced with the corresponding element from the directory stack, as it would be displayed by the dirs builtin invoked with the characters following tilde in the tilde-prefix as an argument (see Section 6.8 [The Directory Stack], page 75). If the tilde-prefix, sans the tilde, consists of a number without a leading `+' or ‘-', '+' is assumed. If the login name is invalid, or the tilde expansion fails, the word is left unchanged. Each variable assignment is checked for unquoted tilde-prefixes immediately following a : ' or the first In these cases, tilde expansion is also performed. Consequently, one may use file names with tildes in assignments to PATH, MAILPATH, and CDPATH, and the shell assigns the expanded value. The following table shows how Bash treats unquoted tilde-prefixes: The value of $HOME EFTA00315872

Chapter 3: Basic Shell Features 19 -/foo 1$HOME/foo' "fred/foo The subdirectory foo of the home directory of the user fred +/foo IPWD/f oo' "-/foo 1{01.1049- }/f oo' The string that would be displayed by `dire +N' -EN The string that would be displayed by `dire +AT' The string that would be displayed by `dirs -N' 3.5.3 Shell Parameter Expansion The `$' character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name. When braces are used, the matching ending brace is the first `}' not escaped by a backslash or within a quoted string, and not within an embedded arithmetic expansion, command substitution, or parameter expansion. The basic form of parameter expansion is ${parameter}. The value of parameter is substituted. The braces are required when parameter is a positional parameter with more than one digit, or when parameter is followed by a character that is not to be interpreted as part of its name. If the first character of parameter is an exclamation point, a level of variable indirection is introduced. Bash uses the value of the variable formed from the rest of parameter as the name of the variable; this variable is then expanded and that value is used in the rest of the substitution, rather than the value of parameter itself. This is known as indirect expansion. The exceptions to this are the expansions of Wprefix*I and S{!name[e]} described below. The exclamation point must immediately follow the left brace in order to introduce indirection. In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion. When not performing substring expansion, Bash tests for a parameter that is unset or null; omitting the colon results in a test only for a parameter that is =set. Put another way, if the colon is included, the operator tests for both existence and that the value is not null; if the colon is omitted, the operator tests only for existence. ${parameter : —word} If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted. Vparameter : word} If parameter is onset or null, the expansion of word is assigned to parameter. The value of parameter is then substituted. Positional parameters and special parameters may not be assigned to in this way. EFTA00315873

20 Bash Reference Manual ${parameter: ?word} If parameter is null or unset, the expansion of word (or a message to that effect if word is not present) is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of parameter is substituted. ${parameter: +word} If parameter is null or unset, nothing is substituted, otherwise the expansion of word is substituted. "{parameter: offset} t{parameter :offset : _length} Expands to up to length characters of parameter starting at the character specified by offset. If length is omitted, expands to the substring of parameter starting at the character specified by offset. length and offset are arithmetic expressions (see Section 6.5 [Shell Arithmetic], page 72). This is referred to as Substring Expansion. length must evaluate to a number greater than or equal to zero. If offset eval- uates to a number less than zero, the value is used as an offset from the end of the value of parameter. If parameter is the result is length positional parameters beginning at offset. If parameter is an array name indexed by 1' or '40, the result is the length members of the array beginning with ${param- eter [of f set]}. A negative offset is taken relative to one greater than the maximum index of the specified array. Note that a negative offset must be sep- arated from the colon by at least one space to avoid being confused with the : expansion. Substring indexing is zero-based unless the positional parameters are used, in which case the indexing starts at 1. ${!prefix*} ${!pref ix0 Expands to the names of variables whose names begin with prefix, separated by the first character of the IFS special variable. ${! name [0]} ${! name [4.]} If name is an array variable, expands to the list of array indices (keys) assigned in name. If name is not an array, expands to 0 if name is set and null otherwise. When is used and the expansion appears within double quotes, each key expands to a separate word. ${#parameter} The length in characters of the expanded value of parameter is substituted. If parameter is or the value substituted is the number of positional parameters. If parameter is an array name subscripted by `*' or 1', the value substituted is the number of elements in the array. ${parameter#word} ${parameter##word} The word is expanded to produce a pattern just as in filename expansion (see Section 3.5.8 (Filename Expansion], page 23). If the pattern matches the be- ginning of the expanded value of parameter, then the result of the expansion is EFTA00315874

Chapter 3: Basic Shell Features 21 the expanded value of parameter with the shortest matching pattern (the `41' case) or the longest matching pattern (the 1#' case) deleted. If parameter is '@' or `*', the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with or `4O, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list. ${parameter%word} “parameter%%mord} The word is expanded to produce a pattern just as in filename expansion. If the pattern matches a trailing portion of the expanded value of parameter, then the result of the expansion is the value of parameter with the shortest matching pattern (the '%' case) or the longest matching pattern (the case) deleted. If parameter is or '4O, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with 'Q' or 440, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list. ${parameter/pattern/string} "{parameter //pattern /string} The pattern is expanded to produce a pattern just as in filename expansion. Parameter is expanded and the longest match of pattern against its value is replaced with string. In the first form, only the first match is replaced. The second form causes all matches of pattern to be replaced with string. If pattern begins with it must match at the beginning of the expanded value of pa- rameter. If pattern begins with W, it must match at the end of the expanded value of parameter. If string is null, matches of pattern are deleted and the / following pattern may be omitted. If parameter is `or or `4O, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with or `*', the substitution operation is applied to each member of the array in turn, and the expansion is the resultant list. 3.5.4 Command Substitution Command substitution allows the output of a command to replace the command itself. Command substitution occurs when a command is enclosed as follows: $ ( command ) or command Bash performs the expansion by executing command and replacing the conunand sub- stitution with the standard output of the command, with any trailing newlines deleted. Embedded newlines are not deleted, but they may be removed during word splitting. The command substitution $ (cat file) can be replaced by the equivalent but faster $ (< file). When the old-style backquote form of substitution is used, backslash retains its literal meaning espt when followed by "', or `V. The first backquote not preceded by a EFTA00315875

22 Bash Reference Manual backslash terminates the command substitution. When using the $ (command) form, all characters between the parentheses make up the command; none are treated specially. Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes. If the substitution appears within double quotes, word splitting and filename expansion are not performed on the results. 3.5.5 Arithmetic Expansion Arithmetic expansion allows the evaluation of an arithmetic expression and the substi- tution of the result. The format for arithmetic expansion is: $(( expression )) The expression is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially. All tokens in the expression undergo parameter ex- pansion, command substitution, and quote removal. Arithmetic expansions may be nested. The evaluation is performed according to the rules listed below (see Section 6.5 [Shell Arithmetic], page 72). If the expression is invalid, Bash prints a message indicating failure to the standard error and no substitution occurs. 3.5.6 Process Substitution Process substitution is supported on systems that support named pipes (FiFos) or the '/dev/fd' method of naming open files. It takes the form of <(list) or >(list) The process list is run with its input or output connected to a FIFO or some file in Vdev/fd% The name of this file is passed as an argument to the current command as the result of the expansion. If the >(list) form is used, writing to the file will provide input for list. If the <(list ) form is used, the file passed as an argument should be read to obtain the output of list. Note that no space may appear between the < or > and the left parenthesis, otherwise the construct would be interpreted as a redirection. When available, process substitution is performed simultaneously with parameter and variable expansion, command substitution, and arithmetic expansion. 3.5.7 Word Splitting The shell scans the results of parameter expansion, command substitution, and arith- metic expansion that did not occur within double quotes for word splitting. The shell treats each character of $IFS as a delimiter, and splits the results of the other expansions into words on these characters. If IFS is =set, or its value is exactly <space><tab><newline>, the default, then any sequence of IFS characters serves to delimit words. If IFS has a value other than the default, then sequences of the whitespace characters space and tab are ignored at the beginning and end of the word, as long as the whitespace EFTA00315876

Chapter 3: Basic Shell Features 23 character is in the value of IFS (an IFS whitespace character). Any character in IFS that is not IFS whitespace, along with any adjacent IFS whitespace characters, delimits a field. A sequence of IFS whitespace characters is also treated as a delimiter. If the value of IFS is null, no word splitting occurs. Explicit null arguments ("" or ') are retained. Unquoted implicit null arguments, resulting from the expansion of parameters that have no values, are removed. If a parameter with no value is expanded within double quotes, a null argument results and is retained. Note that if no expansion occurs, no splitting is performed. 3.5.8 Filename Expansion After word splitting, unless the `-f' option has been set (see Section 4.3 [The Set Malkin), page 51), Bash scans each word for the characters `*', 1', and ['. If one of these characters appears, then the word is regarded as a pattern, and replaced with an alphabetically sorted list of file names matching the pattern. If no matching file names are found, and the shell option nullglob is disabled, the word is left unchanged. If the nullglob option is set, and no matches are found, the word is removed. If the failglob shell option is set, and no matches are found, an error message is printed and the command is not executed. If the shell option nocaseglob is enabled, the match is performed without regard to the case of alphabetic characters. When a pattern is used for filename generation, the character . ' at the start of a filename or immediately following a slash must be matched explicitly, unless the shell option dotglob is set. When matching a file name, the slash character must always be matched explicitly. In other cases, the 1. ' character is not treated specially. See the description of shopt in Section 4.2 [Bash Builtins], page 39, for a description of the nocaseglob, nullglob, failglob, and dotglob options. The GLOBIGNORE shell variable may be used to restrict the set of filenames matching a pattern. If GLOBIGNORE is set, each matching filename that also matches one of the patterns in GLOBIGNORE is removed from the list of matches. The filenames `.' and 1.. ' are always ignored when GLOBIGNORE is set and not null. However, setting GLOBIGNORE to a non-null value has the effect of enabling the dotglob shell option, so all other filenames beginning with a ' will match. lb get the old behavior of ignoring filenames beginning with a make 1.*' one of the patterns in GLOBIGNORE. The dotglob option is disabled when GLOBIGNORE is tinsel 3.5.8.1 Pattern Matching Any character that appears in a pattern, other than the special pattern characters de- scribed below, matches itself. The NUL character may not occur in a pattern. A backslash escapes the following character; the escaping backslash is discarded when matching. The special pattern characters must be quoted if they are to be matched literally. The special pattern characters have the following meanings: Matches any string, including the null string. Matches any single character. EFTA00315877

24 Bash Reference Manual 1...] Matches any one of the enclosed characters. A pair of characters separated by a hyphen denotes a range expression; any character that sorts between those two characters, inclusive, using the current locale's collating sequence and character set, is matched. If the first character following the '1' is a ' or a '' then any character not enclosed is matched. A may be matched by including it as the first or last character in the set. A 1 ' may be matched by including it as the first character in the set. The sorting order of characters in range expressions is determined by the current locale and the value of the LC_COLLATE shell variable, if set. For example, in the default C locale, [a-ft-4 ' is equivalent to [abaixy4 Many locales sort characters in dictionary order, and in these locales ' [a-ft-4' is typically not equivalent to [abcdxyz]'; it might be equivalent to laBbCcDdriCyYz]', for example. To obtain the traditional interpretation of ranges in bracket expressions, you can force the use of the C locale by setting the LC_COLLATE or LC_ALL environment variable to the value 'C'. Within '1' and '3'. character classes can be specified using the syntax 1: class:], where class is one of the following classes defined in the POSIX 1003.2 standard: alnum alpha ascii blank entrl digit graph lower print punct space upper word xdigit A character class matches any character belonging to that class. The word character class matches letters, digits, and the character Within '1' and ', an equivalence class can be specified using the syntax (=c=], which matches all characters with the same collation weight (as defined by the current locale) as the character c. Within '1' and 1 ', the syntax . symbol .] matches the collating symbol symbol. If the extglob shell option is enabled using the shopt builtin, several extended pattern matching operators are recognized. In the following description, a pattern-list is a list of one or more patterns separated by a I'. Composite patterns may be formed using one or more of the following sub-patterns: ?(pattern-list) Nlatches zero or one occurrence of the given patterns. •(pattern-list) Matches zero or more occurrences of the given patterns. + (pat t ern-li et ) Matches one or more occurrences of the given patterns. @(pattern-list) Matches one of the given patterns. !(pattern-list) Matches anything except one of the given patterns. 3.5.9 Quote Removal After the preceding expansions, all unquoted occurrences of the characters `V, ", and """ that did not result from one of the above expansions are removed. EFTA00315878

Chapter 3: Basic Shell Features 25 3.6 Redirections Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell. Redirection may also be used to open and close files for the current shell execution environment. The following redirection operators may precede or appear anywhere within a simple command or may follow a command. Redirections are processed in the order they appear, from left to right. In the following descriptions, if the file descriptor number is omitted, and the first char- acter of the redirection operator is the redirection refers to the standard input (file descriptor 0). If the first character of the redirection operator is `>', the redirection refers to the standard output (file descriptor 1). The word following the redirection operator in the following descriptions, unless other- wise noted, is subjected to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic expansion, quote removal, filename expansion, and word splitting. If it expands to more than one word, Bash reports an error. Note that the order of redirections is significant. For example, the command is > dirlist 2>&1 directs both standard output (file descriptor 1) and standard error (file descriptor 2) to the file dirlist, while the command is 2>&1 > dirlist directs only the standard output to file dirlist, because the standard error was duplicated as standard output before the standard output was redirected to dirlist. Bash handles several filenames specially when they are used in redirections, as described in the following table: /dev/fd/fd If fd is a valid integer, file descriptor fd is duplicated. /dev/stdin File descriptor 0 is duplicated. /dev/stdout File descriptor 1 is duplicated. /dev/stderr File descriptor 2 is duplicated. /dev/tcp/host/port If host is a valid hostname or Internet address, and port is an integer port number or service name, Bash attempts to open a TCP connection to the corresponding socket. /dev/udp/host/port If host is a valid hostname or Internet address, and port is an integer port number or service name, Bash attempts to open a UDP connection to the corresponding socket. A failure to open or create a file causes the redirection to fail. Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell uses internally. EFTA00315879

26 Bash Reference Manual 3.6.1 Redirecting Input Redirection of input causes the file whose name results from the expansion of word to be opened for reading on file descriptor n, or the standard input (file descriptor 0) if n is not specified. The general format for redirecting input is: [n] <word 3.6.2 Redirecting Output Redirection of output causes the file whose name results from the expansion of word to be opened for writing on file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created; if it does exist it is truncated to zero size. The general format for redirecting output is: [n]>[I] word If the redirection operator is `>', and the noclobber option to the set builtin has been enabled, the redirection will fail if the file whose name results from the expansion of word exists and is a regular file. If the redirection operator is `>1', or the redirection operator is `>' and the noclobber option is not enabled, the redirection is attempted even if the file named by word exists. 3.6.3 Appending Redirected Output Redirection of output in this fashion causes the file whose name results from the expan- sion of word to be opened for appending on file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created. The general format for appending output is: [n] »word 3.6.4 Redirecting Standard Output and Standard Error Bash allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of word with this construct. There are two formats for redirecting standard output and standard error: &>word and >&word Of the two forms, the first is preferred. This is semantically equivalent to >word 2>&1 EFTA00315880

Chapter 3: Basic Shell Features 27 3.6.5 Here Documents This type of redirection instructs the shell to read input from the current source until a line containing only word (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command. The format of here-documents is: «[—] word here-document delimiter No parameter expansion, command substitution, arithmetic expansion, or filename ex- pansion is performed on word. If any characters in word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the character sequence \newline is ignored, and `V must be used to quote the characters `V, and "'. If the redirection operator is `«-', then all leading tab characters are stripped front input lines and the line containing delimiter. This allows here-documents within shell scripts to be indented in a natural fashion. 3.6.6 Here Strings A variant of here documents, the format is: «< word The word is expanded and supplied to the conunand on its standard input. 3.6.7 Duplicating File Descriptors The redirection operator [n] <ttword is used to duplicate input file descriptors. If word expands to one or more digits, the file descriptor denoted by n is made to be a copy of that file descriptor. If the digits in word do not specify a file descriptor open for input, a redirection error occurs. If word evaluates to file descriptor n is closed. If n is not specified, the standard input (file descriptor 0) is used. The operator [n] >tword is used similarly to duplicate output file descriptors. If n is not specified, the standard output (file descriptor 1) is used. If the digits in word do not specify a file descriptor open for output, a redirection error occurs. As a special case, if n is omitted, and word does not expand to one or more digits, the standard output and standard error are redirected as described previously. EFTA00315881

28 Bash Reference Manual 3.6.8 Moving File Descriptors The redirection operator [n] <&digit- moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is not specified. digit is closed after being duplicated to n. Similarly, the redirection operator [n] >&digit- moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n is not specified. 3.6.9 Opening File Descriptors for Reading and Writing The redirection operator in] <>word causes the file whose name is the expansion of word to be opened for both reading and writing on file descriptor n, or on file descriptor 0 if n is not specified. If the file does not exist, it is created. 3.7 Executing Commands 3.7.1 Simple Command Expansion When a simple command is executed, the shell performs the following expansions, as- signments, and redirections, from left to right. 1. The words that the parser has marked as variable assignments (those preceding the command name) and redirections are saved for later processing. 2. The words that are not variable assignments or redirections are expanded (see Sec- tion 3.5 [Shell Expansions], page 17). If any words remain after expansion, the first word is taken to be the name of the command and the remaining words are the argu- ments. 3. Redirections are performed as described above (see Section 3.6 [Redirection], page 25). 4. The text after the `.=-' in each variable assignment undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal before being assigned to the variable. If no conunand name results, the variable assignments affect the current shell environ- ment. Otherwise, the variables are added to the environment of the executed command and do not affect the current shell environment. If any of the assignments attempts to assign a value to a readonly variable, an error occurs, and the command exits with a non-zero status. If no command name results, redirections are performed, but do not affect the current shell environment. A redirection error causes the command to exit with a non-zero status. EFTA00315882

Chapter 3: Basic Shell Features 29 If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of the expansions contained a command substitu- tion, the exit status of the command is the exit status of the last command substitution performed. If there were no command substitutions, the command exits with a status of zero. 3.7.2 Command Search and Execution After a command has been split into words, if it results in a simple command and an optional list of arguments, the following actions are taken. 1. If the command name contains no slashes, the shell attempts to locate it. If there exists a shell function by that name, that function is invoked as described in Section 3.3 [Shell Functions], page 14. 2. If the name does not match a function, the shell searches for it in the list of shell builtins. If a match is found, that builtin is invoked. 3. If the name is neither a shell function nor a builtin, and contains no slashes, Bash searches each element of $PATH for a directory containing an executable file by that name. Bash uses a hash table to remember the full pathnames of executable files to avoid multiple PATH searches (see the description of hash in Section 4.1 [Bourne Shell Builtins], page 33). A full search of the directories in $PATH is performed only if the command is not found in the hash table. If the search is unsuccessful, the shell prints an error message and returns an exit status of 127. 4. If the search is successful, or if the command name contains one or more slashes, the shell executes the named program in a separate execution environment. Argument 0 is set to the name given, and the remaining arguments to the command are set to the arguments supplied, if any. 5. If this execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a shell script and the shell executes it as described in Section 3.8 [Shell Scripts], page 32. 6. If the command was not begun asynchronously, the shell waits for the conunand to complete and collects its exit status. 3.7.3 Command Execution Environment The shell has an execution environment, which consists of the following: • open files inherited by the shell at invocation, as modified by redirections supplied to the exec builtin • the current working directory as set by cd, pushd, or popd, or inherited by the shell at invocation • the file creation mode mask as set by umask or inherited front the shell's parent • current traps set by trap • shell parameters that are set by variable assignment or with set or inherited from the shell's parent in the environment EFTA00315883

30 Bash Reference Manual • shell functions defined during execution or inherited from the shell's parent in the environment • options enabled at invocation (either by default or with command-line arguments) or by set • options enabled by shopt • shell aliases defined with alias (see Section 6.6 [Aliases], page 73) • various process ms, including those of background jobs (see Section 3.2.3 [Lists], page 9), the value of n, and the value of $PPID When a simple conunand other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. Unless otherwise noted, the values are inherited from the shell. • the shell's open files, plus any modifications and additions specified by redirections to the command • the current working directory • the file creation mode mask • shell variables and functions marked for export, along with variables exported for the command, passed in the environment (see Section 3.7.4 [Environment], page 30) • traps caught by the shell are reset to the values inherited from the shell's parent, and traps ignored by the shell are ignored A command invoked in this separate environment cannot affect the shell's execution environment. Command substitution, commands grouped with parentheses, and asynchronous com- mands are invoked in a subshell environment that is a duplicate of the shell environment, except that traps caught by the shell are reset to the values that the shell inherited from its parent at invocation. Builtin commands that are invoked as part of a pipeline are also executed in a subshell environment. Changes made to the subshell environment cannot affect the shell's execution environment. If a command is followed by a 1' and job control is not active, the default standard input for the conunand is the empty file 'They/null'. Otherwise, the invoked command inherits the file descriptors of the calling shell as modified by redirections. 3.7.4 Environment When a program is invoked it is given an array of strings called the environment. This is a list of name-value pairs, of the form name=value. Bash provides several ways to manipulate the environment. On invocation, the shell scans its own environment and creates a parameter for each name found, automatically marking it for export to child processes. Executed commands inherit the environment. The export and `declare -x' conunands allow parameters and functions to be added to and deleted from the environment. If the value of a parameter in the environment is modified, the new value becomes part of the environment, replacing the old. The environment inherited by any executed command consists of the shell's initial environment, whose values may be EFTA00315884

Chapter 3: Basic Shell Features 31 modified in the shell, less any pairs removed by the unset and `export -n' commands, plus any additions via the export and 'declare -x' commands. The environment for any simple command or function may be augmented temporarily by prefixing it with parameter assignments, as described in Section 3.4 [Shell Parameters], page 15. These assignment statements affect only the environment seen by that command. If the `-F option is set (see Section 4.3 [The Set Builtin], page 51), then all parameter assignments are placed in the environment for a command, not just those that precede the command name. When Bash invokes an external command, the variable `$: is set to the full path name of the command and passed to that command in its environment. 3.7.5 Exit Status For the shell's purposes, a command which exits with a zero exit status has succeeded. A non-zero exit status indicates failure. This seemingly counter-intuitive scheme is used so there is one well-defined way to indicate success and a variety of ways to indicate various failure modes. When a command terminates on a fatal signal whose number is N, Bash uses the value 128+N as the exit status. If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not executable, the return status is 126. If a command fails because of an error during expansion or redirection, the exit status is greater than zero. The exit status is used by the Bash conditional commands (see Section 3.2.4.2 [Con- ditional Constructs], page 10) and some of the list constructs (see Section 3.2.3 [Lists], page 9). All of the Bash builtins return an exit status of zero if they succeed and a non-zero status on failure, so they may be used by the conditional and list constructs. All builtins return an exit status of 2 to indicate incorrect usage. 3.7.6 Signals When Bash is interactive, in the absence of any traps, it ignores SIGTERM (so that `kill 0' does not kill an interactive shell), and SIGINT is caught and handled (so that the wait builtin is interruptible). When Bash receives a SIGINT, it breaks out of any executing loops. In all cases, Bash ignores SIGQUIT. If job control is in effect (see Chapter 7 [Job Control], page 83), Bash ignores SIGTTIN, SIGTTOU, and SIGTSTP. Non-builtin commands started by Bash have signal handlers set to the values inherited by the shell from its parent. When job control is not in effect, asynchronous commands ignore SIGINT and SIGQUIT in addition to these inherited handlers. Commands run as a result of command substitution ignore the keyboard-generated job control signals SIGTTIN, SIGTTOU, and SIGTSTP. The shell exits by default upon receipt of a SIGHUP. Before exiting, an interactive shell resends the SIGHUP to all jobs, running or stopped. Stopped jobs are sent SIGCONT to ensure that they receive the SIGHUP. To prevent the shell front sending the SIGHUP signal EFTA00315885

32 Bash Reference Manual to a particular job, it should be removed from the jobs table with the disown builtin (see Section 7.2 [Job Control Builtins], page 84) or marked to not receive SIGHUP using disown -h. If the huponexit shell option has been set with shopt (see Section 4.2 [Bash Builtins], page 39), Bash sends a SIGHUP to all jobs when an interactive login shell exits. If Bash is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed until the command completes. When Bash is waiting for an asynchronous command via the wait builtin, the reception of a signal for which a trap has been set will cause the wait builtin to return immediately with an exit status greater than 128, immediately after which the trap is executed. 3.8 Shell Scripts A shell script is a text file containing shell commands. When such a file is used as the first non-option argument when invoking Bash, and neither the `-c' nor `-s' option is supplied (see Section 6.1 [Invoking Bash], page 65), Bash reads and executes commands front the file, then exits. This mode of operation creates a non-interactive shell. The shell first searches for the file in the current directory, and looks in the directories in $PATH if not found there. When Bash runs a shell script, it sets the special parameter 0 to the name of the file, rather than the name of the shell, and the positional parameters are set to the remain- ing arguments, if any are given. If no additional arguments are supplied, the positional parameters are unset. A shell script may be made executable by using the chmod command to turn on the execute bit. When Bash finds such a file while searching the $PATH for a command, it spawns a subshell to execute it. In other words, executing filename arguments is equivalent to executing bash filename arguments if filename is an executable shell script. This subshell reinitializes itself, so that the effect is as if a new shell had been invoked to interpret the script, with the exception that the locations of conunands remembered by the parent (see the description of hash in Section 4.1 [Bourne Shell Builtins], page 33) are retained by the child. Most versions of Unix make this a part of the operating system's command execution mechanism. If the first line of a script begins with the two characters 'it! ', the remainder of the line specifies an interpreter for the program. Thus, you can specify Bash, awk, Perl, or some other interpreter and write the rest of the script file in that language. The arguments to the interpreter consist of a single optional argument following the interpreter name on the first line of the script file, followed by the name of the script file, followed by the rest of the arguments. Bash will perform this action on operating systems that do not handle it themselves. Note that some older versions of Unix limit the interpreter name and argument to a maximum of 32 characters. Bash scripts often begin with #! /bin/bash (assuming that Bash has been installed in `Thin% since this ensures that Bash will be used to interpret the script, even if it is executed under another shell. EFTA00315886

Chapter 4: Shell Builtin Commands 33 4 Shell Builtin Commands Builtin commands are contained within the shell itself. When the name of a builtin com- mand is used as the first word of a simple command (see Section 3.2.1 [Simple Commands], page 8), the shell executes the command directly, without invoking another program. Builtin commands are necessary to implement functionality impossible or inconvenient to obtain with separate utilities. This section briefly the builtins which Bash inherits from the Bourne Shell, as well as the builtin commands which are unique to or have been extended in Bash. Several builtin commands are described in other chapters: builtin commands which provide the Bash interface to the job control facilities (see Section 7.2 [Job Control Builtins], page 84), the directory stack (see Section 6.8.1 [Directory Stack Builtins], page 75), the command history (see Section 9.2 [Bash History Builtins], page 113), and the programmable completion facilities (see Section 8.7 [Programmable Completion Builtins], page 109). Many of the builtins have been extended by POSIX or Bash. Unless otherwise noted, each builtin command documented as accepting options preceded by `-' accepts `--' to signify the end of the options. For example, the :, true, false, and test builtins do not accept options. 4.1 Bourne Shell Builtins The following shell builtin commands are inherited from the Bourne Shell. These com- mands are implemented as specified by the POSIX 1003.2 standard. : (a colon) : [arguments] Do nothing beyond expanding arguments and performing redirections. The return status is zero. . (a period) . filename [arguments] Read and execute commands from the filename argument in the current shell context. If filename does not contain a slash, the PATH variable is used to find filename. When Bash is not in POSIX mode, the current directory is searched if filename is not found in $PATH. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return status is the exit status of the last command executed, or zero if no commands are executed. If filename is not found, or cannot be read, the return status is non-zero. This builtin is equivalent to source. break break [n] Exit from a for, while, until, or select loop. If n is supplied, the nth enclosing loop is exited. n must be greater than or equal to 1. The return status is zero unless n is not greater than or equal to 1. EFTA00315887

34 Bash Reference Manual cd ed [-LI -P] [directory] Change the current working directory to directory. If directory is not given, the value of the HOME shell variable is used. If the shell variable CDPATH exists, it is used as a search path. If directory begins with a slash, CDPATH is not used. The `-P' option means to not follow symbolic links; symbolic links are followed by default or with the `-L' option. If directory is `-', it is equivalent to $OLDPWD. If a non-empty directory name from CDPATH is used, or if `-' is the first argu- ment, and the directory change is successful, the absolute pathname of the new working directory is written to the standard output. The return status is zero if the directory is successfully changed, non-zero oth- erwise. continue continue [n] Resume the next iteration of an enclosing for, while, until, or select loop. If n is supplied, the execution of the nth enclosing loop is resumed. n must be greater than or equal to 1. The return status is zero unless n is not greater than or equal to 1. eval eval [arguments] The arguments are concatenated together into a single command, which is then read and executed, and its exit status returned as the exit status of eval. If there are no arguments or only empty arguments, the return status is zero. exec exec [-el] [-a name] [command [arguments]] If command is supplied, it replaces the shell without creating a new process. If the `-1' option is supplied, the shell places a dash at the beginning of the zeroth arg passed to command. This is what the login program does. The `-e' option causes command to be executed with an empty environment. If `-a' is supplied, the shell passes name as the zeroth argument to command. If no command is specified, redirections may be used to affect the current shell environment. If there are no redirection errors, the return status is zero; otherwise the return status is non-zero. exit exit [n] Exit the shell, returning a status of n to the shell's parent. If n is omitted, the exit status is that of the last command executed. Any trap on EXIT is executed before the shell terminates. export export [-fn] [-p] [name[= value]] Mark each name to be passed to child processes in the environment. If the `-f option is supplied, the names refer to shell functions; otherwise the names EFTA00315888

Chapter 4: Shell Builtin Commands 35 refer to shell variables. The C-n' option means to no longer mark each name for export. If no names are supplied, or if the `-p' option is given, a list of exported names is displayed. The `-p' option displays output in a form that may be reused as input. If a variable name is followed by =value, the value of the variable is set to value. The return status is zero unless an invalid option is supplied, one of the names is not a valid shell variable name, or `-f' is supplied with a name that is not a shell function. getopts getopts optstring name [args] getopts is used by shell scripts to parse positional parameters. optstring con- tains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. The colon CO and question mark (1') may not be used as option characters. Each time it is invoked, getopts places the next option in the shell variable name, initializing name if it does not exist, and the index of the next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used. When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index of the first non-option argument, and name is set to 'V. getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead. getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation diagnostic messages are printed when invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon. If an invalid option is seen, getopts places 'V into name and, if not silent, prints an error message and 'insets OPTARG. If getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed. If a required argument is not found, and getopts is not silent, a question mark (1') is placed in name, OPTARG is onset, and a diagnostic message is printed. If getopts is silent, then a colon (`:') is placed in name and OPTARG is set to the option character found. hash hash [-'r] [-p filename] [-dt] [name] Remember the full pathnames of commands specified as name arguments, so they need not be searched for on subsequent invocations. The commands are found by searching through the directories listed in $PA'fH. The `-p' option EFTA00315889

36 Bash Reference Manual inhibits the path search, and filename is used as the location of name. The `-r' option causes the shell to forget all remembered locations. The `-d' option causes the shell to forget the remembered location of each name. If the `-t' option is supplied, the full pathname to which each name corresponds is printed. If multiple name arguments are supplied with `-t' the name is printed before the hashed full pathname. The `-1.' option causes output to be displayed in a format that may be reused as input. If no arguments are given, or if only `-1' is supplied, information about remembered commands is printed. The return status is zero unless a name is not found or an invalid option is supplied. pwd pwd [-LP] Print the absolute pathname of the current working directory. If the `-P' option is supplied, the pathname printed will not contain symbolic links. If the `-1.' option is supplied, the pathname printed may contain symbolic links. The return status is zero unless an error is encountered while determining the name of the current directory or an invalid option is supplied. readonly readonly [-apf] [name [=value]] .. . Mark each name as readonly. The values of these names may not be changed by subsequent assignment. If the `-f' option is supplied, each name refers to a shell function. The `-a' option means each name refers to an array variable. If no name arguments are given, or if the `-p' option is supplied, a list of all readonly names is printed. The `-p' option causes output to be displayed in a format that may be reused as input. If a variable name is followed by =value, the value of the variable is set to value. The return status is zero unless an invalid option is supplied, one of the name arguments is not a valid shell variable or function name, or the `-f' option is supplied with a name that is not a shell function. return return [n] Cause a shell function to exit with the return value n. If n is not supplied, the return value is the exit status of the last command executed in the function. This may also be used to terminate execution of a script being executed with the . (or source) builtin, returning either n or the exit status of the last command executed within the script as the exit status of the script. Any command associated with the RETURN trap is executed before execution resumes after the function or script. The return status is non-zero if return is used outside a function and not during the execution of a script by . or source. shift shift [n] Shift the positional parameters to the left by n. The positional parameters from n+1 $4 are renamed to $1 . . . $e-n+1. Parameters represented by the numbers $4 to n+1 are unset. n must be a non-negative number less than or equal to $e. If n is zero or greater than $4, the positional parameters are not EFTA00315890

Chapter 4: Shell Builtin Commands 37 changed. If n is not supplied, it is assumed to be 1. The return status is zero unless n is greater than Sit or less than zero, non-zero otherwise. test Evaluate a conditional expression expr. Each operator and operand must be a separate argument. Expressions are composed of the primaries described below in Section 6.4 [Bash Conditional Expressions], page 71. test does not accept any options, nor does it accept and ignore an argument of as signifying the end of options. When the [ form is used, the last argument to the conunand must be a ] . Expressions may be combined using the following operators, listed in decreasing order of precedence. ! expr ( expr ) True if expr is false. Returns the value of expr. This may be used to override the normal precedence of operators. exprl -a expr2 True if both exprl and expr2 are true. exprl -o expr2 True if either exprl or expr2 is true. The test and [ builtins evaluate conditional expressions using a set of rules based on the number of arguments. 0 arguments The expression is false. 1 argument The expression is true if and only if the argument is not null. 2 arguments If the first argument is ! ', the expression is true if and only if the second argument is null. If the first argument is one of the unary conditional operators (see Section 6.4 [Bash Conditional Expres- sions], page 71), the expression is true if the unary test is true. If the first argument is not a valid unary operator, the expression is false. 3 arguments If the second argument is one of the binary conditional operators (see Section 6.4 [Bash Conditional Expressions], page 71), the result of the expression is the result of the binary test using the first and third arguments as operands. If the first argument is ', the value is the negation of the two-argument test using the second and third arguments. If the first argument is exactly 'C' and the third argument is exactly T, the result is the one-argument test of the second argument. Otherwise, the expression is false. The '-a' and '-o' operators are considered binary operators in this case. EFTA00315891

38 Bash Reference Manual 4 arguments If the first argument is ', the result is the negation of the three- argument expression composed of the remaining arguments. Oth- erwise, the expression is parsed and evaluated according to prece- dence using the rules listed above. 5 or more arguments The expression is parsed and evaluated according to precedence using the rules listed above. times times Print out the user and system times used by the shell and its children. The return status is zero. trap trap Elp] [arg] Csigapec .. .] The commands in arg are to be read and executed when the shell receives signal sigspec. If arg is absent (and there is a single sigspec) or equal to `-', each specified signal's disposition is reset to the value it had when the shell was started. If arg is the null string, then the signal specified by each sigspec is ignored by the shell and commands it invokes. If arg is not present and `-p' has been supplied, the shell displays the trap commands associated with each sigspec. If no arguments are supplied, or only `-p' is given, trap prints the list of commands associated with each signal number in a form that may be reused as shell input. The `-1' option causes the shell to print a list of signal names and their corresponding numbers. Each sigspec is either a signal name or a signal number. Signal names are case insensitive and the SIG prefix is optional. If a sigspec is 0 or EXIT, arg is executed when the shell exits. If a sigspec is DEBUG, the command arg is executed before every simple command, for command, case command, select command, every arithmetic for command, and before the first command executes in a shell function. Refer to the description of the extglob option to the ahopt builtin (see Section 4.2 [Bash Builtins], page 39) for details of its effect on the DEBUG trap. If a sigspec is ERR, the command arg is executed whenever a simple command has a non-zero exit status, subject to the following conditions. The ERR trap is not executed if the failed conunand is part of the command list immediately following an until or while keyword, part of the test in an if statement, part of a && or I I list, or if the command's return status is being inverted using I. These are the same conditions obeyed by the errexit option. If a sigspec is RETURN, the command arg is executed each time a shell function or a script executed with the . or source builtins finishes executing. Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals are reset to their original values in a child process when it is created. The return status is zero unless a sigspec does not specify a valid signal. umask EFTA00315892

Chapter 4: Shell Builtin Commands 39 umask [-0 (-Si [mode] Set the shell process's file creation mask to mode. If mode begins with a digit, it is interpreted as an octal number; if not, it is interpreted as a symbolic mode mask similar to that accepted by the ehmod command. If mode is omitted, the current value of the mask is printed. If the `-S' option is supplied without a mode argument, the mask is printed in a symbolic format. If the `-p' option is supplied, and mode is omitted, the output is in a form that may be reused as input. The return status is zero if the mode is successfully changed or if no mode argument is supplied, and non-zero otherwise. Note that when the mode is interpreted as an octal number, each number of the umask is subtracted from 7. Thus, a umask of 022 results in permissions of 755. unset unset [-f v] [name] Each variable or function name is removed. If no options are supplied, or the `-v' option is given, each name refers to a shell variable. If the `-f' option is given, the names refer to shell functions, and the function definition is removed. Readonly variables and functions may not be unset. The return status is zero unless a name is readonly. 4.2 Bash Builtin Commands This section describes builtin commands which are unique to or have been extended in Bash. Some of these commands are specified in the POSIX 1003.2 standard. alias alias [-p] [name[nalue] .] Without arguments or with the `-p' option, alias prints the list of aliases on the standard output in a form that allows them to be reused as input. If arguments are supplied, an alias is defined for each name whose value is given. If no value is given, the name and value of the alias is printed. Aliases are described in Section 6.6 [Aliases], page 73. bind bind [-m keymap] [-1psvPSV] bind [-m keymap] [-q function] [-u function] [-r keyseq] bind [-in keymap] -f filename bind [-in keymap] -x keyseq:shell-command bind [-in keymap] keyseq: function-name bind readline-command Display current Readline (see Chapter 8 [Command Line Editing], page 87) key and function bindings, bind a key sequence to a Readline function or macro, or set a Readline variable. Each non-option argument is a command as it would appear in a a Readline initialization file (see Section 8.3 [Readline Init File], page 90), but each binding or command must be passed as a separate EFTA00315893

40 Bash Reference Manual argument; e.g., "\C-x\C-r":re-read-init-file'. Options, if supplied, have the following meanings: - m keymap Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. -1 List the names of all Readline functions. - p - p - V Display Readline function names and bindings in such a way that they can be used as input or in a Readline initialization file. List current Readline function names and bindings. Display Readline variable names and values in such a way that they can be used as input or in a Readline initialization file. - V List current Readline variable names and values. -s Display Readline key sequences bound to macros and the strings they output in such a way that they can be used as input or in a Readline initialization file. - S Display Readline key sequences bound to macros and the strings they output. - f filename Read key bindings from filename. - q function Query about which keys invoke the named function. - u function Unbind all keys bound to the named function. - r keyseq Remove any current binding for keyseq. - x keyseq: shell-command Cause shell-command to be executed whenever keyseq is entered. The return status is zero unless an invalid option is supplied or an error occurs. builtin builtin [shell-builtin [ergs]] Run a shell builtin, passing it ergs, and return its exit status. This is useful when defining a shell function with the same name as a shell builtin, retaining the functionality of the builtin within the function. The return status is non- zero if shell-builtin is not a shell builtin conunand. caller EFTA00315894

Chapter 4: Shell Builtin Commands 41 caller [expr] Returns the context of any active subroutine call (a shell function or a script executed with the . or source builtins). Without expr, caller displays the line number and source filename of the current subroutine call. If a non-negative integer is supplied as expr, caller displays the line number, subroutine name, and source file corresponding to that position in the current execution call stack. This extra information may be used, for example, to print a stack trace. The current frame is frame 0. The return value is 0 unless the shell is not executing a subroutine call or expr does not correspond to a valid position in the call stack. command command [-pVv] command [arguments .. .] Runs command with arguments ignoring any shell function named command. Only shell builtin commands or commands found by searching the PATH are executed. If there is a shell function named ls, running `command ls' within the function will execute the external command is instead of calling the function recursively. The `-p' option means to use a default value for PATH that is guaranteed to find all of the standard utilities. The return status in this case is 127 if command cannot be found or an error occurred, and the exit status of command otherwise. If either the `-ir or `-v' option is supplied, a description of command is printed. The `-v' option causes a single word indicating the command or file name used to invoke command to be displayed; the `-if' option produces a more verbose description. In this case, the return status is zero if command is found, and non-zero if not. declare declare [-afFirtx] [-p] [name [=value] . . .] Declare variables and give them attributes. If no names are given, then display the values of variables instead. The `-p' option will display the attributes and values of each name. When `-p' is used, additional options are ignored. The `-F" option inhibits the display of function definitions; only the function name and attributes are printed. If the extdebug shell option is enabled using shopt (see Section 4.2 [Bash Builtins], page 39), the source file name and line number where the function is defined are displayed as well. '-F' implies `-f'. The following options can be used to restrict output to variables with the specified attributes or to give variables attributes: - a Each name is an array variable (see Section 6.7 [Arrays], page 74). - f Use function names only. - i The variable is to be treated as an integer; aritlunetic evaluation (see Section 6.5 [Shell Arithmetic], page 72) is performed when the variable is assigned a value. EFTA00315895

42 Bash Reference Manual echo - r - t - x Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset. Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special meaning for variables. Mark each name for export to subsequent commands via the envi- ronment. Using `+' instead of turns off the attribute instead. When used in a function, declare makes each name local, as with the local command. If a variable name is followed by =value, the value of the variable is set to value. The return status is zero unless an invalid option is encountered, an attempt is made to define a function using `-f foo=bar', an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see Section 6.7 [Arrays], page 74), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-existent function with `-r. echo [-neE] [arg ...] Output the ergs, separated by spaces, terminated with a newline. The return status is always 0. If `-n' is specified, the trailing newline is suppressed. If the `-e' option is given, interpretation of the following backslash-escaped char- acters is enabled. The `-E' option disables the interpretation of these escape characters, even on systems where they are interpreted by default. The xpg_ echo shell option may be used to dynamically determine whether or not echo expands these escape characters by default. echo does not interpret `--' to mean the end of options. echo interprets the following escape sequences: \a alert (bell) \b backspace \c suppress trailing newline \e escape \f form feed \n new line \r carriage return \t horizontal tab \v vertical tab \\ backslash EFTA00315896

Chapter 4: Shell Builtin Commands 43 enable help let local \ (Than \nnn \xHH the eight-bit character whose value is the octal value nnn (zero to three octal digits) the eight-bit character whose value is the octal value min (one to three octal digits) the eight-bit character whose value is the hexadecimal value HU (one or two hex digits) enable [-n] [-p] 1-f filename] [-ads] [name . .] Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before disk commands. If '-n' is used, the names become disabled. Otherwise names are enabled. For example, to use the test binary found via $PATH instead of the shell builtin version, type `enable -n test'. If the `-p' option is supplied, or no name arguments appear, a list of shell builtins is printed. With no other arguments, the list consists of all enabled shell builtins. The `-a' option means to list each builtin with an indication of whether or not it is enabled. The `-f' option means to load the new builtin command name from shared object filename, on systems that support dynamic loading. The '-d' option will delete a builtin loaded with '-f'. If there are no options, a list of the shell builtins is displayed. The `-s' option restricts enable to the POSIX special builtins. If `-s' is used with `-f', the new builtin becomes a special builtin (see Section 4.4 [Special Builtins], page 54). The return status is zero unless a name is not a shell builtin or there is an error loading a new builtin from a shared object. help [-a] [pattern] Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern, otherwise a list of the builtins is printed. The `-a' option restricts the information displayed to a short usage synopsis. The return status is zero unless no command matches pattern. let expression [expression] The let builtin allows arithmetic to be performed on shell variables. Each expression is evaluated according to the rules given below in Section 6.5 [Shell Arithmetic), page 72. If the last expression evaluates to 0, let returns 1; otherwise 0 is returned. local [option] name [=value] EFTA00315897

44 Bash Reference Manual For each argument, a local variable named name is created, and assigned value. The option can be any of the options accepted by declare. local can only be used within a function; it makes the variable name have a visible scope restricted to that function and its children. The return status is zero unless local is used outside a function, an invalid name is supplied, or name is a readonly variable. logout logout [n] Exit a login shell, returning a status of n to the shell's parent. printf printf [-v var] format [arguments] Write the formatted arguments to the standard output under the control of the format. The format is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard printf (1) formats, "Ab' causes printf to expand backslash escape sequences in the corresponding argument, (except that Ac' terminates output, backslashes in \ `\"', and `\?' are not removed, and octal escapes beginning with AO' may contain up to four digits), and "Ace causes printf to output the corresponding argument in a format that can be reused as shell input. The '-v' option causes the output to be assigned to the variable var rather than being printed to the standard output. The format is reused as necessary to consume all of the arguments. If the for- mat requires more arguments than are supplied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure. read read [-era] [-a aname] [-d delim] [-n nchars] [-p prompt] [-t time- out] [-u fd] [name .. .] One line is read from the standard input, or from the file descriptor fd supplied as an argument to the '-u' option, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words and their intervening separators assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are assigned empty values. The characters in the value of the IFS variable are used to split the line into words. The backslash character `V may be used to remove any special meaning for the next character read and for line continuation. If no names are supplied, the line read is assigned to the variable REPLY. The return code is zero, unless end-of-file is encountered, read times out, or an invalid file descriptor is supplied as the argument to '-u'. Options, if supplied, have the following meanings: EFTA00315898

Chapter 4: Shell Builtin Commands 45 - a MUMS The words are assigned to sequential indices of the array variable aname, starting at O. All elements are removed from aname before the assignment. Other name arguments are ignored. - d delim The first character of delim is used to terminate the input line, rather than newline. - e Readline (see Chapter 8 [Command Line Editing], page 87) is used to obtain the line. - n nchars read returns after reading nchars characters rather than waiting for a complete line of input. - p prompt Display prompt, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal. shopt - r -s If this option is given, backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not be used as a line continuation. Silent mode. If input is coming from a terminal, characters are not echoed. - t timeout Cause read to time out and return failure if a complete line of input is not read within timeout seconds. This option has no effect if read is not reading input from the terminal or a pipe. - u fd Read input from file descriptor fd. shopt [-pqsu] [-o] [optname .] Toggle the values of variables controlling optional shell behavior. With no options, or with the `-p' option, a list of all settable options is displayed, with an indication of whether or not each is set. The `-p' option causes output to be displayed in a form that may be reused as input. Other options have the following meanings: - s - u -q Enable (set) each optname. Disable (unset) each optname. Suppresses normal output; the return status indicates whether the optname is set or unset. If multiple optname arguments are given with '-q', the return status is zero if all optnames are enabled; non-zero otherwise. - o Restricts the values of optname to be those defined for the '-o' option to the set builtin (see Section 4.3 [The Set Builtin], page 51). EFTA00315899

46 Bash Reference Manual If either '-s' or '-u' is used with no optname arguments, the display is limited to those options which are set or unset, respectively. Unless otherwise noted, the shopt options are disabled (off) by default. The return status when listing options is zero if all optnames are enabled, non- zero otherwise. When setting or unsetting options, the return status is zero unless an optname is not a valid shell option. The list of shopt options is: cdable_vars If this is set, an argument to the cd builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to. cdspell If set, minor errors in the spelling of a directory component in a cd command will be corrected. The errors checked for are transposed characters, a missing character, and a character too many. If a correction is found, the corrected path is printed, and the command proceeds. This option is only used by interactive shells. checkhash If this is set, Bash checks that a command found in the hash table exists before trying to execute it. If a hashed command no longer exists, a normal path search is performed. checkwinsize If set, Bash checks the window size after each command and, if necessary, updates the values of LINES and COLUMNS. cmdhist If set, Bash attempts to save all lines of a multiple-line command in the same history entry. This allows easy re-editing of multi-line commands. dotglob If set, Bash includes filenames beginning with a in the results of filename expansion. execf ail If this is set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the exec builtin command. An interactive shell does not exit if exec fails. expand_aliases If set, aliases are expanded as described below under Aliases, Sec- tion 6.6 [Aliases], page 73. This option is enabled by default for interactive shells. extdebug If set, behavior intended for use by debuggers is enabled: 1. The `-F" option to the declare builtin (see Section 4.2 [Bash Builtins], page 39) displays the source file name and line num- ber corresponding to each function name supplied as an argu- ment. 2. If the command run by the DEBUG trap returns a non-zero value, the next command is skipped and not executed. EFTA00315900

Chapter 4: Shell Builtin Commands 47 3. If the command run by the DEBUG trap returns a value of 2, and the shell is executing in a subroutine (a shell function or a shell script executed by the . or source builtins), a call to return is simulated. 4. BASH_ARGC and BASH_ARGV are updated as described in their descriptions (see Section 5.2 [Bash Variables], page 55). 5. Function tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the DEBUG and RETURN traps. 6. Error tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the ERROR trap. extglob If set, the extended pattern matching features described above (see Section 3.5.8.1 [Pattern Matching], page 23) are enabled. extquote If set, $ 'string' and $"string" quoting is performed within "{parameter} expansions enclosed in double quotes. This option is enabled by default. failglob If set, patterns which fail to match filenames during pathname ex- pansion result in an expansion error. force_f ignore If set, the suffixes specified by the FIGNORE shell variable cause words to be ignored when performing word completion even if the ignored words are the only possible completions. See Section 5.2 [Bash Variables], page 55, for a description of FIGNORE. This option is enabled by default. gnu_errfmt If set, shell error messages are written in the standard GNU error message format. histappend If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exits, rather than overwriting the file. histreedit If set, and Readline is being used, a user is given the opportunity to re-edit a failed history substitution. histverify If set, and Readline is being used, the results of history substitu- tion are not immediately passed to the shell parser. Instead, the resulting line is loaded into the Readline editing buffer, allowing further modification. hostcomplete If set, and Readline is being used, Bash will attempt to perform hostname completion when a word containing a `V is being com- EFTA00315901

48 Bash Reference Manual pleted (see Section 8.4.6 [Commands For Completion], page 103). This option is enabled by default. huponexit If set, Bash will send SIGHUP to all jobs when an interactive login shell exits (see Section 3.7.6 [Signals], page 31). interactive_comments Allow a word beginning with 'It' to cause that word and all remain- ing characters on that line to be ignored in an interactive shell. This option is enabled by default. lithist If enabled, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded newlines rather than using semicolon separators where possible. login_shell The shell sets this option if it is started as a login shell (see Sec- tion 6.1 [Invoking Bash], page 65). The value may not be changed. mailwarn If set, and a file that Bash is checking for mail has been accessed since the Iasi t ime it was checked, the message "The mail in mail- file has been read" is displayed. no_empty_cmd_completion If set, and Readline is being used, Bash will not attempt to search the PATH for possible completions when completion is attempted on an empty line. nocaseglob If set, Bash matches filenames in a case-insensitive fashion when performing filename expansion. nocasematch If set, Bash matches patterns in a case-insensitive fashion when performing matching while executing case or 11 conditional com- mands. nullglob If set, Bash allows filename patterns which match no files to expand to a null string, rather than themselves. progcomp If set, the programmable completion facilities (see Section 8.6 [Pro- grammable Completion], page 107) are enabled. This option is enabled by default. prompt varS If set, prompt strings undergo parameter expansion, command sub- stitution, arithmetic expansion, and quote removal after being ex- panded as described below (see Section 6.9 [Printing a Prompt], page 77). This option is enabled by default. reStri cted_shell The shell sets this option if it is started in restricted mode (see Section 6.10 [The Restricted Shell], page 78). The value may not EFTA00315902

Chapter 4: Shell Builtin Commands 49 be changed. This is not reset when the startup files are executed, allowing the startup files to discover whether or not a shell is re- stricted. shif t_verbose If this is set, the shift builtin prints an error message when the shift count eve.eds the number of positional parameters. sourcepath If set, the source builtin uses the value of PATH to find the directory containing the file supplied as an argument. This option is enabled by default. xpg_echo If set, the echo builtin expands backslash-escape sequences by de- fault. The return status when listing options is zero if all optnames are enabled, non- zero otherwise. When setting or unsetting options, the return status is zero unless an optname is not a valid shell option. source source filename A synonym for . (see Section 4.1 [Bourne Shell Builtins], page 33). type type [-afptP] [name .] For each name, indicate how it would be interpreted if used as a command name. If the `-t' option is used, type prints a single word which is one of `alias', `function', `builtin', `file' or `keyword', if name is an alias, shell function, shell builtin, disk file, or shell reserved word, respectively. If the name is not found, then nothing is printed, and type returns a failure status. If the `-p' option is used, type either returns the name of the disk file that would be executed, or nothing if `-t' would not return `file'. The `-P' option forces a path search for each name, even if `-t' would not return `file'. If a command is hashed, `-p' and `-P' print the hashed value, not necessarily the file that appears first in SPAM. If the '-a' option is used, type returns all of the places that contain an exe- cutable named file. This includes aliases and functions, if and only if the `-p' option is not also used. If the `-f' option is used, type does not attempt to find shell functions, as with the command builtin. The return status is zero if any of the names are found, non-zero if none are found. typeset EFTA00315903

50 Bash Reference Manual typeset [-afFrxi] [-p] [name [=value] . . .] The typeset command is supplied for compatibility with the Korn shell; how- ever, it has been deprecated in favor of the declare builtin command. ulimit ulimit [-acdflmnpstuvSH] [limit] ulimit provides control over the resources available to processes started by the shell, on systems that allow such control. If an option is given, it is interpreted as follows: - S Change and report the soft limit associated with a resource. - H Change and report the hard limit associated with a resource. - a All current limits are reported. - c The maximum size of core files created. - d The maximum size of a process's data segment. - f The maximum size of files created by the shell. -1 The maximum size that may be locked into memory. - m The maximum resident set size. - n The maximum number of open file descriptors. - p The pipe buffer size. -s The maximum stack size. - t The maximum amount of cpu time in seconds. - u The maximum number of processes available to a single user. - v The maximum amount of virtual memory available to the process. If limit is given, it is the new value of the specified resource; the special limit values hard, soft, and unlimited stand for the current hard limit, the current soft limit, and no limit, respectively. Otherwise, the current value of the soft limit for the specified resource is printed, unless the `-H' option is supplied. When setting new limits, if neither `-H' nor `-s' is supplied, both the hard and soft limits are set. If no option is given, then '-f' is assumed. Values are in 1024-byte increments, except for `-t', which is in seconds, `-p', which is in units of 512-byte blocks, and '-n' and '-u', which are unsealed values. The return status is zero unless an invalid option or argument is supplied, or an error occurs while setting a new limit. unalias unalias [-a] [name .. . ] Remove each name from the list of aliases. If '-a' is supplied, all aliases are removed. Aliases are described in Section 6.6 [Aliases], page 73. EFTA00315904

Chapter 4: Shell Builtin Commands 51 4.3 The Set Builtin This builtin is so complicated that it deserves its own section. set set [--abefhkmnptuvxBCHP] [-o option] [argument .. .1 If no options or arguments are supplied, set displays the names and values of all shell variables and functions, sorted according to the current locale, in a format that may be reused as input for setting or resetting the currently-set variables. Read-only variables cannot be reset. In POSIX mode, only shell variables are listed. When options are supplied, they set or onset shell attributes. Options, if spec- ified, have the following meanings: - a - b - e Mark variables and function which are modified or created for ex- port to the environment of subsequent commands. Cause the status of terminated background jobs to be reported immediately, rather than before printing the next primary prompt. Exit immediately if a simple command (see Section 3.2.1 [Simple Commands], page 8) exits with a non-zero status, unless the com- mand that fails is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a && or I I list, or if the command's return status is being inverted using !. A trap on ERR, if set, is executed before the shell exits. - f Disable file name generation (globbing). - h Locate and remember (hash) conunands as they are looked up for execution. This option is enabled by default. - k All arguments in the form of assignment statements are placed in the environment for a command, not just those that precede the command name. - m Job control is enabled (see Chapter 7 [Job Control], page 83). - n Read commands but do not execute them; this may be used to check a script for syntax errors. This option is ignored by interactive shells. - o option-name Set the option corresponding to option-name: allexport Same as -a. braceexpand Same as -B. emacs Use an emacs-style line editing interface (see Chapter 8 [Command Line Editing], page 87). EFTA00315905

52 Bash Reference Manual errexit Same as -e. errtrace Same as -E. functrace Same as -T. hashall Same as -h. h i s texpand Same as -H. history Enable command history, as described in Section 9.1 [Bash History Facilities], page 113. This option is on by default in interactive shells. ignoreeof An interactive shell will not exit upon reading EOF. keyword Same as -k. monitor Same as -m. noclobber Same as -C. noexec Same as -n. noglob Same as -f. nolog Currently ignored. notify Same as -b. nounset Same as -u. onecmd Same as -t. physical Same as -P. pipefail If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands in the pipeline exit suc- cessfully. This option is disabled by default. poaix Change the behavior of Bash where the default oper- ation differs from the POSIX 1003.2 standard to match the standard (see Section 6.11 [Bash POSIX Mode], page 78). This is intended to make Bash behave as a strict superset of that standard. privileged Same as -p. verbose Same as -v. vi Use a vi-style line editing interface. xtrace Same as -x. EFTA00315906

Chapter 4: Shell Builtin Commands 53 - p Turn on privileged mode. In this mode, the $BASH_ENV and $ENV files are not processed, shell functions are not inherited from the environment, and the SHELLOPTS variable, if it appears in the en- vironment, is ignored. If the shell is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supplied, these actions are taken and the effective user id is set to the real user id. If the -p option is supplied at startup, the effective user id is not reset. Turning this option off causes the effective user and group ids to be set to the real user and group ids. - t Exit after reading and executing one command. - u Treat onset variables as an error when performing parameter ex- pansion. An error message will be written to the standard error, and a non-interactive shell will exit. - v Print shell input lines as they are read. - x Print a trace of simple commands, \fBfor\fP commands, \ificaseVP commands, \fBselect\fP commands, and arithmetic \ fBforMP commands and their arguments or associated word lists after they are expanded and before they are executed. The value of the PS4 variable is expanded and the resultant value is printed before the command and its expanded arguments. - B The shell will perform brace expansion (see Section 3.5.1 [Brace Expansion], page 17). This option is on by default. - C Prevent output redirection using '>', `>&', and `o' from overwriting existing files. - E If set, any trap on ERR is inherited by shell functions, conunand substitutions, and commands executed in a subshell environment. The ERR trap is normally not inherited in such cases. - H Enable `I ' style history substitution (see Section 9.3 [History In- teraction], page 115). This option is on by default for interactive shells. - P If set, do not follow symbolic links when performing commands such as cd which change the current directory. The physical direc- tory is used instead. By default, Bash follows the logical chain of directories when performing commands which change the current directory. For example, if Vusr/sys' is a symbolic link to lusr/local/sys' then: $ cd /usr/sys; echo $PWD /usr/sys $ cd . .; pwd /usr It set -P is on, then: EFTA00315907

54 Bash Reference Manual $ Cd /usr/sys; echo $1)14D /usr/local/sys $ ed ..; pwd /usr/local -T If set, any trap on DEBUG and RETURN are inherited by shell func- tions, command substitutions, and commands executed in a sub- shell environment. The DEBUG and RETURN traps are normally not inherited in such cases. If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters are set to the ar- guments, even if some of them begin with a `-'. Signal the end of options, cause all remaining arguments to be assigned to the positional parameters. The `-x' and `-v' options are turned off. If there are no arguments, the positional parameters remain unchanged. Using `+' rather than `-' causes these options to be turned off. The options can also be used upon invocation of the shell. The current set of options may be found in $-. The remaining N arguments are positional parameters and are assigned, in order, to $1, $2, . . . $N. The special parameter # is set to N. The return status is always zero unless an invalid option is supplied. 4.4 Special Builtins For historical reasons, the POSIX 1003.2 standard has classified several builtin commands as special. When Bash is executing in POSIX mode, the special builtins differ from other builtin commands in three respects: 1. Special builtins are found before shell functions during command lookup. 2. If a special builtin returns an error status, a non-interactive shell exits. 3. Assignment statements preceding the command stay in effect in the shell environment after the command completes. When Bash is not executing in POSIX mode, these builtins behave no differently than the rest of the Bash builtin commands. The Bash Posix mode is described in Section 6.11 [Bash POSIX Mode], page 78. These are the POSIX special builtins: break : . continue eval exec exit export readonly return set shift trap unset EFTA00315908

Chapter 5: Shell Variables 55 5 Shell Variables This chapter describes the shell variables that Bash uses. Bash automatically assigns default values to a number of variables. 5.1 Bourne Shell Variables Bash uses certain shell variables in the same way as the Bourne shell. In some cases, Bash assigns a default value to the variable. CDPATH A colon-separated list of directories used as a search path for the cd builtin command. HOME The current user's home directory; the default for the cd builtin command. The value of this variable is also used by tilde expansion (see Section 3.5.2 [Tilde Expansion], page 18). IFS A list of characters that separate fields; used when the shell splits words as part of expansion. MAIL If this parameter is set to a filename and the MAILPATH variable is not set, Bash informs the user of the arrival of mail in the specified file. MAILPATH A colon-separated list of filenames which the shell periodically checks for new mail. Each list entry can specify the message that is printed when new mail arrives in the mail file by separating the file name front the message with a 'V. When used in the text of the message, $_ expands to the name of the current mail file. OPTARC The value of the last option argument processed by the getopts builtin. OPTIND The index of the last option argument processed by the getopts builtin. PATH A colon-separated list of directories in which the shell looks for commands. A zero-length (null) directory name in the value of PATH indicates the current directory. A null directory name may appear as two adjacent colons, or as an initial or trailing colon. PSi The primary prompt string. The default value is As- \v\ $ '. See Section 6.9 [Printing a Prompt], page 77, for the complete list of escape sequences that are expanded before PS1 is displayed. PS2 The secondary prompt string. The default value is 5. '. 5.2 Bash Variables These variables are set or used by Bash, but other shells do not normally treat them specially. A few variables used by Bash are described in different chapters: variables for controlling the job control facilities (see Section 7.3 [Job Control Variables], page 86). BASH The full pathname used to execute the current instance of Bash. EFTA00315909

56 Bash Reference Manual BASH_ARGC An array variable whose values are the number of parameters in each frame of the current bash execution call stack. The number of parameters to the current subroutine (shell function or script executed with . or source) is at the top of the stack. When a subroutine is executed, the number of parameters passed is pushed onto BASH_ARGC. The shell sets BASH_ARGC only when in extended debugging mode (see Section 4.2 [Bash Builtins], page 39 for a description of the extdebug option to the shopt BASH_ARGV An array variable containing all of the parameters in the current bash execution call stack. The final parameter of the last subroutine call is at the top of the stack; the first parameter of the initial call is at the bottom. When a subroutine is executed, the parameters supplied are pushed onto BASH_ARGV. The shell sets BASH_ARGV only when in extended debugging mode (see Section 4.2 [Bash Bullfinch page 39 for a description of the extdebug option to the shopt builtin). BASH_COMMAND The command currently being executed or about to be executed, unless the shell is executing a command as the result of a trap, in which case it is the command executing at the time of the trap. BASH_ENV If this variable is set when Bash is invoked to execute a shell script, its value is expanded and used as the name of a startup file to read before executing the script. See Section 6.2 [Bash Startup Files], page 67. BASH_EXECUTION_STRING The command argument to the `-c' invocation option. BASH_LINENO An array variable whose members are the line numbers in source files corre- sponding to each member of FUNCNAME. ${BASH_LINENO[$i]} is the line number in the source file where l(FUNCNAME [$i] } was called. The correspond- ing source file name is EBASH_SOURCE Dill. Use LINENO to obtain the current line number. BASH REMATCH An array variable whose members are assigned by the `="' binary operator to the U conditional conunand (see Section 3.2.4.2 [Conditional Constructs], page 10). The element with index 0 is the portion of the string matching the entire regular expression. The element with index n is the portion of the string matching the nth parenthesized subexpression. This variable is read-only. BASH_SOURCE An array variable whose members are the source filenames corresponding to the elements in the FUNCNAME array variable. BASH_SUBSHELL Incremented by one each time a subshell or subshell environment is spawned. The initial value is 0. EFTA00315910

Chapter 5: Shell Variables 57 BASH_VERSINFO A readonly array variable (see Section 6.7 [Arrays], page 74) whose members hold version information for this instance of Bash. The values assigned to the array members are as follows: BASH_VERSINFO [0] The major version number (the release). BASH_VERSINFO [1] The minor version number (the version). BASH_VERSINFO [2] The patch level. BASH_VERSINFO [3] The build version. BASH_VERSINFO [4] The release status (e.g., betal). BASH_VERSINFO [5] The value of MACHTYPE. BASH_VERSION The version number of the current instance of Bash. COLUMNS Used by the select builtin command to determine the terminal width when printing selection lists. Automatically set upon receipt of a SIGWINCH. COMP_CWORD An index into ${COMP_WORDS} of the word containing the current cursor po- sition. This variable is available only in shell functions invoked by the pro- grammable completion facilities (see Section 8.6 [Programmable Completion], page 107). COMP_LINE The current command line. This variable is available only in shell functions and external conunands invoked by the programmable completion facilities (see Section 8.6 [Programmable Completion], page 107). COMP_POINT The index of the current cursor position relative to the beginning of the current command. If the current cursor position is at the end of the current conunand, the value of this variable is equal to ${#COMP_LINE}. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Section 8.6 [Programmable Completion], page 107). COMP_WORDBREAKS The set of characters that the Readline library treats as word separators when performing word completion. If COMP_WORDBREAKS is unset, it loses its special properties, even if it is subsequently reset. COMP_WORDS An array variable consisting of the individual words in the current command line. This variable is available only in shell functions invoked by the pro- EFTA00315911

58 Bash Reference Manual grammable completion facilities (see Section 8.6 [Programmable Completion], page 107). COMPREPLY An array variable from which Bash reads the possible completions generated by a shell function invoked by the programmable completion facility (see Sec- tion 8.6 [Programmable Completion], page 107). DIRSTACK An array variable containing the current contents of the directory stack. Direc- tories appear in the stack in the order they are displayed by the dire builtin. Assigning to members of this array variable may be used to modify directories already in the stack, but the pushd and popd builtins must be used to add and remove directories. Assignment to this variable will not change the cur- rent directory. If DIRSTACK is unset, it loses its special properties, even if it is subsequently reset. EMACS If Bash finds this variable in the environment when the shell starts with value `V, it assumes that the shell is running in an emacs shell buffer and disables line editing. EUID The numeric effective user id of the current user. This variable is readonly. FCEDIT The editor used as a default by the `-e' option to the fc builtin command. FIGNORE A colon-separated list of suffixes to ignore when performing filename comple- tion. A file name whose suffix matches one of the entries in FIGNORE is excluded from the list of matched file names. A sample value is .o FUNCNAME An array variable containing the names of all shell functions currently in the execution call stack. The element with index 0 is the name of any currently- executing shell function. The bottom-most element is "main". This variable exists only when a shell function is executing. Assignments to FUNCNAME have no effect and return an error status. If FUNCNAME is unset, it loses its special properties, even if it is subsequently reset. GLOBIGNORE A colon-separated list of patterns defining the set of filenames to be ignored by filename expansion. If a filename matched by a filename expansion pattern also matches one of the patterns in GLOBIGNORE, it is removed from the list of matches. GROUPS An array variable containing the list of groups of which the current user is a member. Assignments to GROUPS have no effect and return an error status. If GROUPS is unset, it loses its special properties, even if it is subsequently reset. histchars Up to three characters which control history expansion, quick substitution, and tokenization (see Section 9.3 [History Interaction], page 115). The first charac- ter is the history expansion character, that is, the character which signifies the start of a history expansion, normally `I'. The second character is the character which signifies `quick substitution' when seen as the first character on a line, normally The optional third character is the character which indicates that EFTA00315912

Chapter 5: Shell Variables 59 the remainder of the line is a comment when found as the first character of a word, usually 'It'. The history comment character causes history substitution to be skipped for the remaining words on the line. It does not necessarily cause the shell parser to treat the rest of the line as a comment. HISTCMD The history number, or index in the history list, of the current command. If HISTC10 is unset, it loses its special properties, even if it is subsequently reset. HISTCONTROL A colon-separated list of values controlling how commands are saved on the history list. If the list of values includes `ignorespace', lines which begin with a space character are not saved in the history list. A value of `ignoredups' causes lines which match the previous history entry to not be saved. A value of `ignoreboth' is shorthand for `ignorespace' and `ignoredups'. A value of `erasedups' causes all previous lines matching the current line to be removed from the history list before that line is saved. Any value not in the above list is ignored. If HISTCONTROL is unset, or does not include a valid value, all lines read by the shell parser are saved on the history list, subject to the value of HISTIGNORE. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of HISTCONTROL. HISTFILE The name of the file to which the command history is saved. The default value is `"/.bash history'. HISTFILESIZE The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than that number of lines. The history file is also truncated to this size after writing it when an interactive shell exits. The default value is 500. HISTIGNORE A colon-separated list of patterns used to decide which conunand lines should be saved on the history list. Each pattern is anchored at the beginning of the line and must match the complete line (no implicit `■' is appended). Each pattern is tested against the line after the checks specified by HISTCONTROL are applied. In addition to the normal shell pattern matching characters, `ft' matches the previous history line. le may be escaped using a backslash; the backslash is removed before attempting a match. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of HISTIGNORE. HISTIGNORE subsumes the function of HISTCONTROL. A pattern of is identical to ignoredups, and a pattern of `1 ] *' is identical to ignorespace. Combining these two patterns, separating them with a colon, provides the functionality of ignoreboth. HISTSIZE The maximum number of commands to remember on the history list. The default value is 500. EFTA00315913

60 Bash Reference Manual HISTTIMEFORMAT If this variable is set and not null, its value is used as a format string for stritime to print the time stamp associated with each history entry displayed by the history bath's. If this variable is set, time stamps are written to the history file so they may be preserved across shell sessions. HOSTFILE Contains the name of a file in the same format as letahosts' that should be read when the shell needs to complete a hostname. The list of possible hostname completions may be changed while the shell is running; the next time hostname completion is attempted after the value is changed, Bash adds the contents of the new file to the existing list. If HOSTFILE is set, but has no value, Bash attempts to read letahosts' to obtain the list of possible hostname completions. When HOSTFILE is unset, the hostname list is cleared. HOSTNAME The name of the current host. HOSTTYPE A string describing the machine Bash is running on. IGNOREEOF Controls the action of the shell on receipt of an EOF character as the sole input. If set, the value denotes the number of consecutive EOF characters that can be read as the first character on an input line before the shell will exit. If the variable exists but does not have a numeric value (or has no value) then the default is 10. If the variable does not exist, then EOF signifies the end of input to the shell. This is only in effect for interactive shells. INPUTRC The name of the Readline initialization file, overriding the default of `/. inputre'. LANG Used to determine the locale category for any category not specifically selected with a variable starting with LC_. LC_ALL This variable overrides the value of LANG and any other LC_ variable specifying a locale category. LC_COLLATE This variable determines the collation order used when sorting the results of filename expansion, and determines the behavior of range expressions, equiv- alence classes, and collating sequences within filename expansion and pattern matching (see Section 3.5.8 [Filename Expansion], page 23). LC_CTYPE This variable determines the interpretation of characters and the behavior of character classes within filename expansion and pattern matching (see Sec- tion 3.5.8 [Filename Expansion], page 23). LC_MESSAGES This variable determines the locale used to translate double-quoted strings pre- ceded by a `$' (see Section 3.1.2.5 [Locale Translation], page 7). LC_NUMERIC This variable determines the locale category used for number formatting. LINENO The line number in the script or shell function currently executing. EFTA00315914

Chapter 5: Shell Variables 61 LINES Used by the select builtin command to determine the column length for print- ing selection lists. Automatically set upon receipt of a SIGWINCH. MACHTYPE A string that hilly describes the system type on which Bash is executing, in the standard GNU cpu-company-system format. MA ILCHECK How often (in seconds) that the shell should check for mail in the files specified in the MAILPATH or MAIL variables. The default is 60 seconds. When it is time to check for mail, the shell does so before displaying the primary prompt. If this variable is unset, or set to a value that is not a number greater than or equal to zero, the shell disables mail checking. OLDPWD The previous working directory as set by the cd builtin. OPTERR If set to the value 1, Bash displays error messages generated by the getopts builtin command. OSTYPE A string describing the operating system Bash is running on. P I P ES TATUS An array variable (see Section 6.7 [Arrays], page 74) containing a list of exit sta- tus values from the processes in the most-recently-executed foreground pipeline (which may contain only a single command). POSIXLY_CORRECT If this variable is in the environment when bash starts, the shell enters POSIX mode (see Section 6.11 [Bash POSIX Mode], page 78) before reading the startup files, as if the `--posix' invocation option had been supplied. If it is set while the shell is running, bash enables POSIX mode, as if the command set -o posix had been executed. PPID The process ID of the shell's parent process. This variable is readonly. PROMPT_COMMAND If set, the value is interpreted as a command to execute before the printing of each primary prompt ($PSI). PS3 The value of this variable is used as the prompt for the select command. If this variable is not set, the select command prompts with 1? ' PS4 The value is the prompt printed before the command line is echoed when the `-x' option is set (see Section 4.3 [The Set Builtin], page 51). The first character of PS4 is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is 4+ '. PWD The current working directory as set by the cd builtin. RANDOM Each time this parameter is referenced, a random integer between 0 and 32767 is generated. Assigning a value to this variable seeds the random number gen- erator. REPLY The default variable for the read builtin. EFTA00315915

Bash Reference Manual SECONDS This variable expands to the number of seconds since the shell was started. Assignment to this variable resets the count to the value assigned, and the expanded value becomes the value assigned plus the number of seconds since the assignment. SHELL The full pathname to the shell is kept in this environment variable. If it is not set when the shell starts, Bash assigns to it the full pathname of the current user's login shell. SHELLOPTS A colon-separated list of enabled shell options. Each word in the list is a valid argument for the '-o' option to the set builtin command (see Section 4.3 [The Set Builtin], page 51). The options appearing in SHELLOPTS are those reported as 'on' by 'set -o'. If this variable is in the environment when Bash starts up, each shell option in the list will be enabled before reading any startup files. This variable is readonly. SHIM. Incremented by one each time a new instance of Bash is started. This is intended to be a count of how deeply your Bash shells are nested. TIMEFORMAT The value of this parameter is used as a format string specifying how the tim- ing information for pipelines prefixed with the time reserved word should be displayed. The "I,' character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions. %% A literal T. %[p] [lilt The elapsed time in seconds. %[p] [1]0 The number of CPU seconds spent in user mode. %[p] [1] 5 The number of CPU seconds spent in system mode. %P The CPU percentage, computed as (%U + %S) / %R. The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values of p greater than 3 are changed to 3. If p is not specified, the value 3 is used. The optional 1 specifies a longer format, including minutes, of the form MAImSS.FFs. The value of p determines whether or not the fraction is included. If this variable is not set, Bash acts as if it had the value $ ' nreal \ t%31R annex t %31U nays \t%3191 If the value is null, no timing information is displayed. A trailing newline is added when the format string is displayed. TMOUT If set to a value greater than zero, TMOUT is treated as the default timeout for the read builtin (see Section 4.2 [Bash Builtins], page 39). The select command (see Section 3.2.4.2 [Conditional Constructs], page 10) terminates if input does not arrive after TMOUT seconds when input is coming from a terminal. EFTA00315916

Chapter 5: Shell Variables 63 TMPDIR UID In an interative shell, the value is interpreted as the number of seconds to wait for input after issuing the primary prompt when the shell is interactive. Bash terminates after that number of seconds if input does not arrive. If set, Bash uses its value as the name of a directory in which Bash creates temporary files for the shell's use. The numeric real user id of the current user. This variable is readonly. EFTA00315917

64 Bash Reference Manual EFTA00315918

Chapter 6: Bash Features 6 Bash Features This section describes features unique to Bash. 6.1 Invoking Bash 65 bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o option] [-0 shopt_option] (ar- gument . ..] bash [long-opt] [-abef hkmnptuvxdBCDHP] [-0 option] [-0 shopt_option] -c string [ar- gument . ..] bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-0 option] [-0 shopt_option] [ar- gument . .] In addition to the single-character shell command-line options (see Section 4.3 [The Set Builtin], page 51), there are several multi-character options that you can use. These options must appear on the command line before the single-character options to be recognized. - -debugger Arrange for the debugger profile to be executed before the shell starts. Turns on extended debugging mode (see Section 4.2 [Bash Builtins], page 39 for a description of the extdebug option to the shopt builtin) and shell function tracing (see Section 4.3 [The Set Builtin], page 51 for a description of the -o functrace option). - -dump-po-strings A list of all double-quoted strings preceded by is printed on the standard output in the GNU gettext PO (portable object) file format. Equivalent to `-D' except for the output format. - -dump-strings Equivalent to `-D'. --help Display a usage message on standard output and exit sucessfully. --init-f ile filename --rcf ile filename Execute commands from filename (instead of Dl.bashre) in an interactive shell. --login Equivalent to '-1'. --noediting Do not use the GNU Readline library (see Chapter 8 [Command Line Editing], page 87) to read command lines when the shell is interactive. - -noprof ile Don't load the system-wide start up file letc/profile' or any of the personal initialization files "V . bash_prof i le'. '"/.bash_login', or "V . prof ile' when Bash is invoked as a login shell. - -norc Don't read the ""/.bashre initialization file in an interactive shell. This is on by default if the shell is invoked as sh. EFTA00315919

66 Bash Reference Manual - -pos ix Change the behavior of Bash where the default operation differs from the POSIX 1003.2 standard to match the standard. This is intended to make Bash behave as a strict superset of that standard. See Section 6.11 [Bash POSIX Mode], page 78, for a description of the Bash POSIX mode. - -restricted Make the shell a restricted shell (see Section 6.10 [The Restricted Shell], page 78). - -verbose Equivalent to `-v'. Print shell input lines as they're read. - -version Show version information for this instance of Bash on the standard output and exit successfully. There are several single-character options that may be supplied at invocation which are not available with the set builtin. - c string Read and execute commands from string after processing the options, then exit. Any remaining arguments are assigned to the positional parameters, starting with $0. - i Force the shell to run interactively. Interactive shells are described in Section 6.3 [Interactive Shells], page 69. -1 Make this shell act as if it had been directly invoked by login. When the shell is interactive, this is equivalent to starting a login shell with `exec -1 bash'. When the shell is not interactive, the login shell startup files will be executed. `exec bash -1' or `exec bash --login' will replace the current shell with a Bash login shell. See Section 6.2 [Bash Startup Files], page 67, for a description of the special behavior of a login shell. - r Make the shell a restricted shell (see Section 6.10 [The Restricted Shell], page 78). - a If this option is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell. - D A list of all double-quoted strings preceded by `$' is printed on the standard output. These are the strings that are subject to language translation when the current locale is not C or POSIX (see Section 3.1.2.5 [Locale Translation], page 7). This implies the `-n' option; no commands will be executed. Ell 0 [shopt_option] shopt_option is one of the shell options accepted by the shopt builtin (see Chapter 4 [Shell Builtin Commands], page 33). If shopt_option is present, '-0' sets the value of that option; `4-0' unsets it. If shopt_option is not supplied, the names and values of the shell options accepted by shopt are printed on the standard output. If the invocation option is `4-0', the output is displayed in a format that may be reused as input. EFTA00315920

Chapter 6: Bash Features 67 A -- signals the end of options and disables further option processing. Any arguments after the -- are treated as filenames and arguments. A login shell is one whose first character of argument zero is `-', or one invoked with the '--login' option. An interactive shell is one started without non-option arguments, unless `-s' is specified, without specifying the `-e' option, and whose input and output are both connected to terminals (as determined by isatty (3)), or one started with the `-i' option. See Section 6.3 [Interactive Shells], page 69, for more information. If arguments remain after option processing, and neither the `-e' nor the `-s' option has been supplied, the first argument is assumed to be the name of a file containing shell commands (see Section 3.8 [Shell Scripts], page 32). When Bash is invoked in this fashion, $0 is set to the name of the file, and the positional parameters are set to the remaining arguments. Bash reads and executes commands from this file, then exits. Bash's exit status is the exit status of the last command executed in the script. If no commands are executed, the exit status is 0. 6.2 Bash Startup Files This section describs how Bash executes its startup files. If any of the files exist but cannot be read, Bash reports an error. Tildes are expanded in file names as described above under Tilde Expansion (see Section 3.5.2 [Tilde Expansion], page 18). Interactive shells are described in Section 6.3 [Interactive Shells], page 69. Invoked as an interactive login shell, or with '--login' When Bash is invoked as an interactive login shell, or as a non-interactive shell with the '--login' option, it first reads and executes commands from the file Veto/profile', if that file exists. After reading that file, it looks for `"/.bash_profile', "tbash_login% and `V.profile', in that order, and reads and executes commands from the first one that exists and is readable. The 4--noprofile' option may be used when the shell is started to inhibit this behavior. When a login shell exits, Bash reads and executes commands from the file `tbash_logout% if it exists. Invoked as an interactive non-login shell When an interactive shell that is not a login shell is started, Bash reads and executes commands from "1.bashre, if that file exists. This may be inhibited by using the `--nore option. The `--rcfile file' option will force Bash to read and execute commands from file instead of ` ./.bashrc'. So, typically, your "V .bash_profile' contains the line if -f V.bashrc ); then . V.bashre; fi after (or before) any login-specific initializations. EFTA00315921

68 Bash Reference Manual Invoked non-interactively When Bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command were executed: if [ -n "SBASH_ENV" ; then . "SBASH_ENV"; fi but the value of the PATH variable is not used to search for the file name. As noted above, if a non-interactive shell is invoked with the option, Bash attempts to read and execute commands front the login shell startup tiles. Invoked with name sh If Bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of ah as closely as possible, while conforming to the POSIX standard as well. When invoked as an interactive login shell, or as a non-interactive shell with the login' option, it first attempts to read and execute commands from Vete/profile' and "1. prof ile', in that order. The `--noprofile option may be used to inhibit this behavior. When invoked as an interactive shell with the name sh, Bash looks for the variable ENV, expands its value if it is defined, and uses the expanded value as the name of a file to read and execute. Since a shell invoked as sh does not attempt to read and execute commands front any other startup files, the `-refile' option has no effect. A non-interactive shell invoked with the name sh does not attempt to read any other startup files. When invoked as sh, Bash enters POSIX mode after the startup files are read. Invoked in POSIX mode When Bash is started in POSIX mode, as with the `--posix' conunand line option, it follows the POSIX standard for startup files. In this mode, interactive shells expand the ENV variable and commands are read and executed from the file whose name is the expanded value. No other startup files are read. Invoked by remote shell daemon Bash attempts to determine when it is being nm by the remote shell daemon, usually rand. If Bash determines it is being run by rshd, it reads and executes commands from `V.bashre, if that file exists and is readable. It will not do this if invoked as sh. The '--nore option may be used to inhibit this behavior, and the `--refile' option may be used to force another file to be read, but rshd does not generally invoke the shell with those options or allow them to be specified. EFTA00315922

Chapter 6: Bash Features 69 Invoked with unequal effective and real IHD/GIDS If Bash is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supplied, no startup files are read, shell functions are not inherited from the environment, the SHELLOPTS variable, if it appears in the environment, is ignored, and the effective user id is set to the real user id. If the -p option is supplied at invocation, the startup behavior is the same, but the effective user id is not reset. 6.3 Interactive Shells 6.3.1 What is an Interactive Shell? An interactive shell is one started without non-option arguments, unless `-s' is specified, without specifiying the `-c' option, and whose input and error output are both connected to terminals (as determined by isatty(3)), or one started with the option. An interactive shell generally reads from and writes to a user's terminal. The `-s' invocation option may be used to set the positional parameters when an inter- active shell is started. 6.3.2 Is this Shell Interactive? To determine within a startup script whether or not Bash is running interactively, test the value of the `-' special parameter. It contains i when the shell is interactive. For example: case "$-" in sit) echo This shell is interactive ; ; *) echo This shell is not interactive ; ; esac Alternatively, startup scripts may examine the variable PSi; it is unset in non-interactive shells, and set in interactive shells. Thus: if -z "$PSI" ]; then echo This shell is not interactive else echo This shell is interactive fi 6.3.3 Interactive Shell Behavior When the shell is running interactively, it changes its behavior in several ways. 1. Startup files are read and executed as described in Section 6.2 [Bash Startup Files], page 67. 2. Job Control (see Chapter 7 (Job Control], page 83) is enabled by default. When job control is in effect, Bash ignores the keyboard-generated job control signals SIGITIN, SIGTTOU, and SIGTSTP. EFTA00315923

70 Bash Reference Manual 3. Bash expands and displays PS1 before reading the first line of a command, and ex- pands and displays PS2 before reading the second and subsequent lines of a multi-line command. 4. Bash executes the value of the PR0MPT_C0MMAND variable as a command before printing the primary prompt, $1,91 (see Section 5.2 (Bash Variables], page 55). 5. Headline (see Chapter 8 [Command Line Editing], page 87) is used to read commands from the user's terminal. 6. Bash inspects the value of the ignoreeof option to set -o instead of exiting imme- diately when it receives an E0F on its standard input when reading a command (see Section 4.3 [The Set Builtin], page 51). 7. Command history (see Section 9.1 [Bash History Facilities], page 113) and history expansion (see Section 9.3 [History Interaction], page 115) are enabled by default. Bash will save the command history to the file named by $HISTFILE when an interactive shell exits. 8. Alias expansion (see Section 6.6 [Aliases], page 73) is performed by default. 9. In the absence of any traps, Bash ignores SIGTERM (see Section 3.7.6 (Signals], page 31). 10. In the absence of any traps, SIGINT is caught and handled ((see Section 3.7.6 [Signals], page 31). SIGINT will interrupt some shell builtins. 11. An interactive login shell sends a SIGHUP to all jobs on exit if the hupoxexit shell option has been enabled (see Section 3.7.6 [Signals], page 31). 12. The `-n' invocation option is ignored, and `set -n' has no effect (see Section 4.3 (The Set Builtin], page 51). 13. Bash will check for mail periodically, depending on the values of the MAIL, MAILPATH, and MAILCHECK shell variables (see Section 5.2 [Bash Variables], page 55). 14. Expansion errors due to references to unbound shell variables after `set -u' has been enabled will not cause the shell to exit (see Section 4.3 [The Set Builtin], page 51). 15. The shell will not exit on expansion errors caused by var being unset or null in Vvar : ?word} expansions (see Section 3.5.3 [Shell Parameter Expansion], page 19). 16. Redirection errors encountered by shell builtins will not cause the shell to exit. 17. When running in POSIX mode, a special builtin returning an error status will not cause the shell to exit (see Section 6.11 [Bash POSIX Mode], page 78). 18. A failed exec will not cause the shell to exit (see Section 4.1 [Bourne Shell Builtins], page 33). 19. Parser syntax errors will not cause the shell to exit. 20. Simple spelling correction for directory arguments to the cd builtin is enabled by default (see the description of the cdspell option to the shopt builtin in Section 4.2 [Bash Builtins], page 39). 21. The shell will check the value of the 'MUT variable and exit if a command is not read within the specified number of seconds after printing $1,91 (see Section 5.2 [Bash Variables], page 55). EFTA00315924

Chapter 6: Bash Features 71 6.4 Bash Conditional Expressions Conditional expressions are used by the [ [ compound command and the test and [ builtin commands. Expressions may be unary or binary. Unary expressions are often used to examine the status of a file. There are string operators and numeric comparison operators as well. If the file argument to one of the primaries is of the form idev/f d/W, then file descriptor N is checked. If the file argument to one of the primaries is one of Vdevistdin', Idevistdout', or ldevistdere, file descriptor 0, 1, or 2, respectively, is checked. Unless otherwise specified, primaries that operate on files follow symbolic links and operate on the target of the link, rather than the link itself. - a file - b file - c file - d file - e file - f file -g file - h file - k file - p file - r file - s file - t fd - u file - w file - x file - 0 file - G file - L file -S file - N file 'flue if file exists. 'flue if file exists and is a block special file. 'flue if file exists and is a character special file. 'flue if file exists and is a directory. 'flue if file exists. 'flue if file exists and is a regular file. 'flue if file exists and its set-group-id bit is set. 'flue if file exists and is a symbolic link. 'flue if file exists and its "sticky" bit is set. 'flue if file exists and is a named pipe (FIFO). 'flue if file exists and is readable. 'flue if file exists and has a size greater than zero. 'flue if file descriptor fd is open and refers to a terminal. 'flue if file exists and its set-u.ser-id bit is set. 'flue if file exists and is writable. 'flue if file exists and is executable. 'flue if file exists and is owned by the effective user id. 'flue if file exists and is owned by the effective group id. 'flue if file exists and is a symbolic link. 'flue if file exists and is a socket. 'flue if file exists and has been modified since it was last read. filel -nt file2 'flue if filel is newer (according to modification date) than file2, or if filel exists and file2 does not. filel -ot file2 'flue if filel is older than file2, or if file2 exists and filel does not. EFTA00315925

72 Bash Reference Manual filel -ef file2 'Due if Mel and file2 refer to the same device and inode numbers. - o optname 'Due if shell option optname is enabled. The list of options appears in the description of the '-o' option to the set builtin (see Section 4.3 (The Set Builtin], page 51). -z string nue if the length of string is zero. - n string string 'flue if the length of string is non-zero. stringl == string2 True if the strings are equal. `=' may be used in place of `==' for strict POSIX compliance. stringl != string2 True if the strings are not equal. stringl < string2 True if stringl sorts before string2 lexicographically in the current locale. stringl > string2 'flue if stringl sorts after string2 lexicographically in the current locale. 'erg.' OP arg2 OP is one of `-eq', `-ne', `-gt', or `-ge'. These arithmetic binary operators return true if argl is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to arg2, respectively. Argl and arg2 may be positive or negative integers. 6.5 Shell Arithmetic The shell allows arithmetic expressions to be evaluated, as one of the shell expansions or by the let and the option to the declare builtins. Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error. The operators and their precedence, associativity, and values are the same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence. id++ id-- variable post-increment and post-decrement ++id --id variable pre-increment and pre-decrement - + unary minus and plus ! logical and bitwise negation ** exponentiation EFTA00315926

Chapter 6: Bash Features 73 * / % multiplication, division, remainder + - addition, subtraction « » left and right bitwise shifts <= >= < > comparison equality and inequality bitwise AND bitwise exclusive OR I bitwise OR && logical AND I I logical OR expr ? expr : expr conditional operator /. -= <<= -= 1= assignment exprl , expr2 comma Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax. A shell variable that is null or onset evaluates to 0 when referenced by name without using the parameter expansion syntax. The value of a variable is evaluated as an arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using `declare is assigned a value. A null value evaluates to 0. A shell variable need not have its integer attribute turned on to be used in an expression. Constants with a leading 0 are interpreted as octal numbers. A leading `Ox' or 'Or denotes hexadecimal. Otherwise, numbers take the form [base#]n, where base is a decimal number between 2 and 64 representing the arithmetic base, and a is a number in that base. If base# is omitted, then base 10 is used. The digits greater than 9 are represented by the lowercase letters, the uppercase letters, 'Q', and `_', in that order. If base is less than or equal to 36, lowercase and uppercase letters may be used interchangeably to represent numbers between 10 and 35. Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above. 6.6 Aliases Aliases allow a string to be substituted for a word when it is used as the first word of a simple command. The shell maintains a list of aliases that may be set and =set with the alias and =alias builtin commands. EFTA00315927

74 Bash Reference Manual The first word of each simple command, if =quoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. The characters " '=' and any of the shell metacharacters or quoting characters listed above may not appear in an alias name. The replacement text may contain any valid shell input, including shell metacharacters. The first word of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second time. This means that one may alias is to "ls -F", for instance, and Bash does not try to recursively expand the replacement text. If the last character of the alias value is a space or tab character, then the next command word following the alias is also checked for alias expansion. Aliases are created and listed with the alias command, and removed with the =alias command. There is no mechanism for using arguments in the replacement text, as in csh. If arguments are needed, a shell function should be used (see Section 3.3 [Shell Functions], page 14). Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see Section 4.2 [Bash Builtins], page 39). The rules concerning the definition and use of aliases are somewhat confusing. Bash always reads at least one complete line of input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias. This behavior is also an issue when functions are executed. Aliases are expanded when a function definition is read, not when the function is executed, because a function definition is itself a compound command. As a consequence, aliases defined in a function are not available until after that function is executed. To be safe, always put alias definitions on a separate line, and do not use alias in compound commands. For almost every purpose, shell functions are preferred over aliases. 6.7 Arrays Bash provides one-dimensional array variables. Any variable may be used as an array; the declare builtin will explicitly declare an array. There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. Arrays are zero-based. An array is created automatically if any variable is assigned to using the syntax name [subscript]=value The subscript is treated as an arithmetic expression that must evaluate to a number greater than or equal to zero. lb explicitly declare an array, use declare -a name The syntax declare -a name [subscript] EFTA00315928

Chapter 6: Bash Features 75 is also accepted; the subscript is ignored. Attributes may be specified for an array variable using the declare and readonly builtins. Each attribute applies to all members of an array. Arrays are assigned to using compound assignments of the form name=(valuel valuen) where each value is of the form [[subscr ipt] =] string. If the optional subscript is sup- plied, that index is assigned to; otherwise the index of the element assigned is the last index assigned to by the statement plus one. Indexing starts at zero. This syntax is also accepted by the declare builtin. Individual array elements may be assigned to using the name [subscript]=value syntax introduced above. Any element of an array may be referenced using ${name [subscript] }. The braces are required to avoid conflicts with the shell's filename expansion operators. If the subscript is 'V or 40, the word expands to all members of the array name. These subscripts differ only when the word appears within double quotes. If the word is double-quoted, ${name [*]1 expands to a single word with the value of each array member separated by the first character of the IFS variable, and ${name [0] } expands each element of name to a separate word. When there are no array members, "{name [0] expands to nothing. If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. This is analogous to the expansion of the special parameters and `*'. Eltname [subscript) } expands to the length of ${name [subscript)}. If subscript is '0' or `4.', the expansion is the number of elements in the array. Referencing an array variable without a subscript is equivalent to referencing element zero. The unset builtin is used to destroy arrays. unset name[subscript] destroys the array element at index subscript. Care must be taken to avoid unwanted side effects caused by filename generation. unset name, where name is an array, removes the entire array. A subscript of 40 or `V also removes the entire array. The declare, local, and readonly builtins each accept a `-a' option to specify an array. The read builtin accepts a '-a' option to assign a list of words read from the standard input to an array, and can read values from the standard input into individual array elements. The set and declare builtins display array values in a way that allows them to be reused as input. 6.8 The Directory Stack The directory stack is a list of recently-visited directories. The pushd builtin adds direc- tories to the stack as it changes the current directory, and the popd builtin removes specified directories front the stack and changes the current directory to the directory removed. The dirs builtin displays the contents of the directory stack. The contents of the directory stack are also visible as the value of the DIRSTACK shell variable. 6.8.1 Directory Stack Builtins din EFTA00315929

76 Bash Reference Manual dirs [+N I -N] [-elpv] Display the list of currently remembered directories. Directories are added to the list with the pushd command; the popd command removes directories from the list. +N Displays the Nth directory (counting from the left of the list printed by dirs when invoked without options), starting with zero. - N Displays the Nth directory (counting from the right of the list printed by dirs when invoked without options), starting with zero. - e Clears the directory stack by deleting all of the elements. -1 Produces a longer listing; the default listing format uses a tilde to denote the home directory. - p Causes dirs to print the directory stack with one entry per line. popd pushd - v Causes dirs to print the directory stack with one entry per line, prefixing each entry with its index in the stack. popd [+N I - N] [- n] Remove the top entry from the directory stack, and ed to the new top directory. When no arguments are given, popd removes the top directory from the stack and performs a ed to the new top directory. The elements are numbered from 0 starting at the first directory listed with din; i.e., popd is equivalent to popd +0. +N - N Removes the Nth directory (counting from the left of the list printed by dirs), starting with zero. Removes the Nth directory (counting from the right of the list printed by dirs), starting with zero. Suppresses the normal change of directory when removing directo- ries from the stack, so that only the stack is manipulated. pushd [dir I +N I -N] [-n] Save the current directory on the top of the directory stack and then cd to dir. With no arguments, pushd exchanges the top two directories. +N Brings the Nth directory (counting from the left of the list printed by dirs, starting with zero) to the top of the list by rotating the stack. - N Brings the Nth directory (counting from the right of the list printed by dirs, starting with zero) to the top of the list by rotating the stack. - n Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated. dir Makes the current working directory be the top of the stack, and then executes the equivalent of `ed dir'. eds to dir. EFTA00315930

Chapter 6: Bash Features 77 6.9 Controlling the Prompt The value of the variable PROMPT_COMMAND is examined just before Bash prints each primary prompt. If PROMPT_COMMAND is set and has a non-null value, then the value is executed just as if it had been typed on the command line. In addition, the following table describes the special characters which can appear in the prompt variables: \a A bell character. \d The date, in "Weekday Month Date" format (e.g., "The May 26"). \D{format} The format is passed to strftime(3) and the result is inserted into the prompt string; an empty format results in a locale-specific time representation. The braces are required. \e An escape character. \h The hostname, up to the first `.'. \H The hostname. \j The number of jobs currently managed by the shell. \1 The basename of the shell's terminal device name. \n A newline. \r A carriage return. \s The name of the shell, the basename of $0 (the portion following the final slash). \t The time, in 24-hour HH:MM:SS format. \T The time, in 12-hour HH:MM:SS format. \@ The time, in 12-hour am/pm format. \A The time, in 24-hour HH:MM format. \u The username of the current user. \v The version of Bash (e.g., 2.00) \V The release of Bash, version + patchlevel (e.g., 2.00.0) \w The current working directory, with $HOME abbreviated with a tilde. \W The basename of $PWD, with $HOME abbreviated with a tilde. \! The history number of this conunand. \# The conunand number of this command. \$ If the effective uid is 0, #, otherwise $. \nnn The character whose ASCII code is the octal value mm. \\ A backslash. EFTA00315931

78 Bash Reference Manual \ C Begin a sequence of non-printing characters. This could be used to embed a terminal control sequence into the prompt. \ End a sequence of non-printing characters. The command number and the history number are usually different: the history number of a command is its position in the history list, which may include commands restored from the history file (see Section 9.1 [Bash History Facilities], page 113), while the command number is the position in the sequence of commands executed during the current shell session. After the string is decoded, it is expanded via parameter expansion, command substi- tution, arithmetic expansion, and quote removal, subject to the value of the promptvars shell option (see Section 4.2 (Bash Builtins], page 39). 6.10 The Restricted Shell If Bash is started with the name rbash, or the `--restricted' or `-r' option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environ- ment more controlled than the standard shell. A restricted shell behaves identically to bash with the exception that the following are disallowed or not performed: • Changing directories with the cd builtin. • Setting or tmsetting the values of the SHELL, PATH, ENV, or BASH_ENV variables. • Specifying conunand names containing slashes. • Specifying a filename containing a slash as an argument to the . builtin command. • Specifying a filename containing a slash as an argument to the `-p' option to the hash builtin command. • Importing function definitions front the shell environment at startup. • Parsing the value of SHELLOPTS front the shell environment at startup. • Redirecting output using the 5', 51', €<>', la', and `».' redirection operators. • Using the exec builtin to replace the shell with another command. • Adding or deleting builtin commands with the '-f' and `-d' options to the enable builtin. • Using the enable builtin command to enable disabled shell builtins. • Specifying the `-p' option to the command builtin. • Turning off restricted mode with `set -Fr' or `set +o restricted'. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is executed (see Section 3.8 [Shell Scripts], page 32), rbash turns off any restrictions in the shell spawned to execute the script. 6.11 Bash POSIX Mode Starting Bash with the `--posix' conunand-line option or executing `set -o pos ix' while Bash is running will cause Bash to conform more closely to the Pow( 1003.2 standard by EFTA00315932

Chapter 6: Bash Features 79 changing the behavior to match that specified by POSIX in areas where the Bash default differs. When invoked as sh, Bash enters POSIX mode after reading the startup files. The following list is what's changed when `POSIX mode' is in effect: 1. When a command in the hash table no longer exists, Bash will re-search $PATII to find the new location. This is also available with ishopt -s checkhash'. 2. The message printed by the job control code and builtins when a job exits with a non-zero status is `Done(status)'. 3. The message printed by the job control code and builtins when a job is stopped is `Stopped(signame)', where signame is, for example, SIGTSTP. 4. The bg builtin uses the required format to describe each job placed in the background, which does not include an indication of whether the job is the current or previous job. 5. Reserved words appearing in a context where reserved words are recognized do not undergo alias expansion. 6. The POSIX 1003.2 PS1 and PS2 expansions of 'V to the history number and `I !' to `!' are enabled, and parameter expansion is performed on the values of PS1 and PS2 regardless of the setting of the promptvars option. 7. The POSIX 1003.2 startup files are executed ($E.NV) rather than the normal Bash files. 8. Tilde expansion is only performed on assignments preceding a command name, rather than on all assignment statements on the line. 9. The default history file is `"/ .sh_history' (this is the default value of $HISTFILE). 10. The output of `kill -1' prints all the signal names on a single line, separated by spaces, without the `SIG' prefix. 11. The kill builtin does not accept signal names with a `SIG' prefix. 12. Non-interactive shells exit if filename in . filename is not found. 13. Non-interactive shells exit if a syntax error in an arithmetic expansion results in an invalid expression. 14. Redirection operators do not perform filename expansion on the word in the redirection unless the shell is interactive. 15. Redirection operators do not perform word splitting on the word in the redirection. 16. Function names must be valid shell names. That is, they may not contain characters other than letters, digits, and underscores, and may not start with a digit. Declaring a function with an invalid name causes a fatal syntax error in non-interactive shells. 17. POSIX 1003.2 special builtins are found before shell functions during command lookup. 18. If a Posix 1003.2 special builtin returns an error status, a non-interactive shell exits. The fatal errors are those listed in the POSIX.2 standard, and include things like passing incorrect options, redirection errors, variable assignment errors for assignments preceding the command name, and so on. 19. If CDPATH is set, the cd builtin will not implicitly append the current directory to it. This means that cd will fail if no valid directory name can be constructed from any of the entries in $CDPATH, even if the a directory with the same name as the name given as an argument to cd exists in the current directory. EFTA00315933

80 Bash Reference Manual 20. A non-interactive shell exits with an error status if a variable assignment error occurs when no command name follows the assignment statements. A variable assignment error occurs, for example, when trying to assign a value to a readonly variable. 21. A non-interactive shell exits with an error status if the iteration variable in a for statement or the selection variable in a select statement is a readonly variable. 22. Process substitution is not available. 23. Assignment statements preceding POSIX 1003.2 special builtins persist in the shell en- vironment after the builtin completes. 24. Assignment statements preceding shell function calls persist in the shell environment after the function returns, as if a POSIX special builtin command had been executed. 25. The export and readonly builtin commands display their output in the format re- quired by Posix 1003.2. 26. The trap builtin displays signal names without the leading SIG. 27. The trap builtin doesn't check the first argument for a possible signal specification and revert the signal handling to the original disposition if it is, unless that argument consists solely of digits and is a valid signal number. If users want to reset the handler for a given signal to the original disposition, they should use as the first argument. 28. The . and source builtins do not search the current directory for the filename argument if it is not found by searching PATH. 29. Subshells spawned to execute command substitutions inherit the value of the `-e' option from the parent shell. When not in POSIX mode, Bash clears the `-e' option in such subshells. 30. Alias expansion is always enabled, even in non-interactive shells. 31. When the alias builtin displays alias definitions, it does not display them with a leading `alias ' unless the `-p' option is supplied. 32. When the set builtin is invoked without options, it does not display shell function names and definitions. 33. When the set builtin is invoked without options, it displays variable values without quotes, unless they contain shell metacharacters, even if the result contains nonprinting characters. 34. When the cd builtin is invoked in logical mode, and the pathname constructed from $PWD and the directory name supplied as an argument does not refer to an existing directory, al will fail instead of falling back to physical mode. 35. When the pwd builtin is supplied the `-P' option, it resets $PWD to a pathname containing no symlinks. 36. The pwd builtin verifies that the value it prints is the same as the current directory, even if it is not asked to check the file system with the `-1, ' option. 37. When listing the history, the fc builtin does not include an indication of whether or not a history entry has been modified. 38. The default editor used by fc is ed. 39. The type and command builtins will not report a non-executable file as having been found, though the shell will attempt to execute such a file if it is the only so-named file found in SPATE EFTA00315934

Chapter 6: Bash Features 81 40. The vi editing mode will invoke the vi editor directly when the `v' command is run, instead of checking $FCEDIT and $EDITOR. 41. When the xpg_echo option is enabled, Bash does not attempt to interpret any ar- guments to echo as options. Each argument is displayed, after escape characters are converted. There is other POSIX 1003.2 behavior that Bash does not implement by default even when in POSIX mode. Specifically: 1. The fc builtin checks $EDITOR as a program to edit history entries if FCEDIT is unset, rather than defaulting directly to ed. fc uses ed if EDITOR is unset. 2. As noted above, Bash requires the xpg_echo option to be enabled for the echo builtin to be fully conformant. Bash can be configured to be posix-conformant by default, by specifying the `--enable-strict-posix-default' to configure when building (see Section 10.8 [Optional Features], page 121). EFTA00315935

82 Bash Reference Manual EFTA00315936

Chapter 7: Job Control 83 7 Job Control This chapter discusses what job control is, how it works, and how Bash allows you to access its facilities. 7.1 Job Control Basics Job control refers to the ability to selectively stop (suspend) the execution of processes and continue (resume) their execution at a later point. A user typically employs this facility via an interactive interface supplied jointly by the system's terminal driver and Bash. The shell associates a job with each pipeline. It keeps a table of currently executing jobs, which may be listed with the jobs command. When Bash starts a job asynchronously, it prints a line that looks like: 11] 25647 indicating that this job is job number 1 and that the process ID of the last process in the pipeline associated with this job is 25647. All of the processes in a single pipeline are members of the same job. Bash uses the job abstraction as the basis for job control. To facilitate the implementation of the user interface to job control, the operating system maintains the notion of a current terminal process group ID. Members of this process group (processes whose process group ID is equal to the current terminal process group in) receive keyboard-generated signals such as SIGINT. These processes are said to be in the foreground. Background processes are those whose process group ID differs from the terminal's; such processes are immune to keyboard-generated signals. Only foreground processes are allowed to read from or write to the terminal. Background processes which attempt to read from (write to) the terminal are sent a SIGITIN (SIGITOU) signal by the terminal driver, which, unless caught, suspends the process. If the operating system on which Bash is running supports job control, Bash contains facilities to use it. Typing the suspend character (typically "I', Control-Z) while a process is running causes that process to be stopped and returns control to Bash. Typing the delayed suspend character (typically Control-Y) causes the process to be stopped when it attempts to read input front the terminal, and control to be returned to Bash. The user then manipulates the state of this job, using the bg command to continue it in the background, the fg command to continue it in the foreground, or the kill command to kill it. A "Z' takes effect immediately, and has the additional side effect of causing pending output and typeahead to be discarded. There are a number of ways to refer to a job in the shell. The character introduces a job name. Job number n may be referred to as "/.n'. The symbols 'WA' and "kr' refer to the shell's notion of the current job, which is the last job stopped while it was in the foreground or started in the background. A single (with no accompanying job specification) also refers to the current job. The previous job may be referenced using In output pertaining to jobs (e.g., the output of the jobs command), the current job is always flagged with a `+', and the previous job with a `-'. A job may also be referred to using a prefix of the name used to start it, or using a substring that appears in its command line. For example, Ice' refers to a stopped ce job. EFTA00315937

84 Bash Reference Manual Using Th e', on the other hand, refers to any job containing the string `ce' in its command line. If the prefix or substring matches more than one job, Bash reports an error. Simply naming a job can be used to bring it into the foreground: 1,1' is a synonym for 'fg %1', bringing job 1 from the background into the foreground. Similarly, la &' resumes job 1 in the background, equivalent to `bg %1' The shell learns immediately whenever a job changes state. Normally, Bash waits until it is about to print a prompt before reporting changes in a job's status so as to not interrupt any other output. If the `-b' option to the set builtin is enabled, Bash reports such changes immediately (see Section 4.3 [The Set Builtin], page 51). Any trap on SIGCHLD is executed for each child process that exits. If an attempt to exit Bash is made while jobs are stopped, the shell prints a message warning that there are stopped jobs. The jobs command may then be used to inspect their status. If a second attempt to exit is made without an intervening command, Bash does not print another warning, and the stopped jobs are terminated. 7.2 Job Control Builtins bg bg [jobspec . ..] Resume each suspended job jobspec in the background, as if it had been started with 1'. If jobspec is not supplied, the current job is used. The return status is zero unless it is run when job control is not enabled, or, when run with job control enabled, any jobspec was not found or specifies a job that was started without job control. fg 4 [jobspec] Resume the job jobspec in the foreground and make it the current job. If jobspec is not supplied, the current job is used. The return status is that of the command placed into the foreground, or non-zero if run when job control is disabled or, when run with job control enabled, jobspec does not specify a valid job or jobspec specifies a job that was started without job control. jobs jobs 1-lnprs] [jobspec] jobs -x command [arguments] The first form lists the active jobs. The options have the following meanings: -1 List process IDs in addition to the normal information. - n - p - r - s Display information only about jobs that have changed status since the user was last notified of their status. List only the process ID of the job's process group leader. Restrict output to running jobs. Restrict output to stopped jobs. EFTA00315938

Chapter 7: Job Control 85 If jobspec is given, output is restricted to information about that job. If jobspec is not supplied, the status of all jobs is listed. If the `-x' option is supplied, jobs replaces any jobspec found in command or arguments with the corresponding process group ID, and executes command, passing it arguments, returning its exit status. kill kill [-s sigspec] [-n signum] [-sigspec] jobspec or pid kill -1 [exit_status] Send a signal specified by sigspec or signum to the process named by job specifi- cation jobspec or process ID pid. sigspec is either a case-insensitive signal name such as SIGINT (with or without the SIG prefix) or a signal number; signum is a signal number. If sigspec and signum are not present, SIGTERM is used. The `-1' option lists the signal names. If any arguments are supplied when '-1' is given, the names of the signals corresponding to the arguments are listed, and the return status is zero. exit_status is a number specifying a signal number or the exit status of a process terminated by a signal. The return status is zero if at least one signal was successfully sent, or non-zero if an error occurs or an invalid option is encountered. wait wait [jobspec or pid .. .] Wait until the child process specified by each process ID pid or job specification jobspec exits and return the exit status of the last command waited for. If a job spec is given, all processes in the job are waited for. If no arguments are given, all currently active child processes are waited for, and the return status is zero. If neither jobspec nor pid specifies an active child process of the shell, the return status is 127. disown disown Far] [-11] [jobspec .1 Without options, each jobspec is removed from the table of active jobs. If the `-h' option is given, the job is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If jobspec is not present, and neither the `-a' nor `-r' option is supplied, the current job is used. If no jobspec is supplied, the `-a' option means to remove or mark all jobs; the `-r' option without a jobspec argument restricts operation to running jobs. suspend suspend [-f] Suspend the execution of this shell until it receives a SIGCONT signal. The `-f' option means to suspend even if the shell is a login shell. When job control is not active, the kill and wait builtins do not accept jobspec argu- ments. They must be supplied process IDS. EFTA00315939

86 Bash Reference Manual 7.3 Job Control Variables auto_resume This variable controls how the shell interacts with the user and job control. If this variable exists then single word simple commands without redirections are treated as candidates for resumption of an existing job. There is no ambiguity allowed; if there is more than one job beginning with the string typed, then the most recently accessed job will be selected. The name of a stopped job, in this context, is the command line used to start it. If this variable is set to the value `exact', the string supplied must match the name of a stopped job exactly; if set to `substring', the string supplied needs to match a substring of the name of a stopped job. The `substring' value provides functionality analogous to the "/3' job ID (see Section 7.1 [Job Control Basics], page 83). If set to any other value, the supplied string must be a prefix of a stopped job's name; this provides functionality analogous to the 'I.' job ID. EFTA00315940

Chapter 8: Command Line Editing 87 8 Command Line Editing This chapter describes the basic features of the GNU command line editing interface. Command line editing is provided by the Readline library, which is used by several different programs, including Bash. 8.1 Introduction to Line Editing The following paragraphs describe the notation used to represent keystrokes. The text C-k is read as 'Control-K' and describes the character produced when the @ key is pressed while the Control key is depressed. The text M-k is read as 'Meta-K' and describes the character produced when the Meta key (if you have one) is depressed, and the key is pressed. The Meta key is labeled (XL'!) on many keyboards. On keyboards with two keys labeled (ALT) (usually to either side of the space bar), the (AL'!) on the left side is generally set to work as a Meta key. The (ALT) key on the right may also be configured to work as a Meta key or may be configured as some other modifier, such as a Compose key for typing accented characters. If you do not have a Meta or Qty key, or another key working as a Meta key, the identical keystroke can be generated by typing first, and then typing @. Either process is known as metafying the 4@ key. The text M-C-k is read as 'Meta-Control-k' and describes the character produced by metafying C-k. In addition, several keys have their own names. Specifically, (DELL OM, (LTD), (Pr), 8E)r, and •C all stand for themselves when seen in this text, or in an init file (see Section 8.3 [Readline Init File], page 90). If your keyboard lacks a (LPD) key, typing C will produce the desired character. The M key may be labeled (Return) or (Enter) on some keyboards. 8.2 Readline Interaction Often during an interactive session you type in a long line of text, only to notice that the first word on the line is misspelled. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press (Rn). You do not have to be at the end of the line to press (6ET); the entire line is accepted regardless of the location of the cursor within the line. 8.2.1 Readline Bare Essentials In order to enter characters into the line, simply type them. The typed character appears where the cursor was, and then the cursor moves one space to the right. If you mistype a character, you can use your erase character to back up and delete the mistyped character. EFTA00315941

88 Bash Reference Manual Sometimes you may mistype a character, and not notice the error until you have typed several other characters. In that case, you can type C-b to move the cursor to the left, and then correct your mistake. Afterwards, you can move the cursor to the right with C-f. When you add text in the middle of a line, you will notice that characters to the right of the cursor are 'pushed over' to make room for the text that you have inserted. Likewise, when you delete text behind the cursor, characters to the right of the cursor are 'pulled back' to fill in the blank space created by the removal of the text. A list of the bare essentials for editing the text of an input line follows. C-b C-f (DEL) C-d Move back one character. Move forward one character. or== Delete the character to the left of the cursor. Delete the character underneath the cursor. Printing characters Insert the character into the line at the cursor. or C-x C-u Undo the last editing command. You can undo all the way back to an empty line. (Depending on your configuration, the (backspace) key be set to delete the character to the left of the cursor and the (a key set to delete the character underneath the cursor, like C-d, rather than the character to the left of the cursor.) 8.2.2 Headline Movement Commands The above table describes the most basic keystrokes that you need in order to do editing of the input line. For your convenience, many other commands have been added in addition to C-b, C-f, C-d, and (DEL). Here are some commands for moving more rapidly about the line. C-a Move to the start of the line. C-e Move to the end of the line. Move forward a word, where a word is composed of letters and digits. Move backward a word. Clear the screen, reprinting the current line at the top. Notice how C-f moves forward a character, while M-f moves forward a word. It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words. EFTA00315942

Chapter 8: Command Line Editing 89 8.2.3 Readline Killing Commands Killing text means to delete the text from the line, but to save it away for later use, usually by yanking (re-inserting) it back into the line. (Tut' and `paste' are more recent jargon for `kill' and `yank'.) If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later. When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it all. The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line. Here is the list of commands for killing text. C-k Kill the text from the current cursor position to the end of the line. M-d Kill from the cursor to the end of the current word, or, if between words, to the end of the next word. Word boundaries are the same as those used by ?Ff. M- EL Kill from the cursor the start of the current word, or, if between words, to the start of the previous word. Word boundaries are the same as those used by M-b. C-te Kill from the cursor to the previous whitespace. This is different than M- because the word boundaries differ. (DEL) Here is how to yank the text back into the line. Yanking means to copy the most- recently-killed text from the kill buffer. C-y Yank the most recently killed text back into the buffer at the cursor. Rotate the kill-ring, and yank the new top. You can only do this if the prior command is C-y or M-y. 8.2.4 Readline Arguments You can pass numeric arguments to Readline commands. Sometimes the argument acts as a repeat count, other times it is the sign of the argument that is significant. If you pass a negative argument to a command which normally acts in a forward direction, that command will act in a backward direction. For example, to kill text back to the start of the line, you might type 11-- C-k'. The general way to pass numeric arguments to a command is to type meta digits before the command. If the first `digit' typed is a minus sign (`-'), then the sign of the argument will be negative. Once you have typed one meta digit to get the argument started, you can type the remainder of the digits, and then the command. For example, to give the C-d command an argument of 10, you could type `14-1 0 C-d', which will delete the next ten characters on the input line. EFTA00315943

90 Bash Reference Manual 8.2.5 Searching for Commands in the History Readline provides commands for searching through the command history (see Section 9.1 [Bash History Facilities], page 113) for lines containing a specified string. There are two search modes: incremental and non-incremental. Incremental searches begin before the user has finished typing the search string. As each character of the search string is typed, Readline displays the next entry from the history matching the string typed so far. An incremental search requires only as many characters as needed to find the desired history entry. To search backward in the history for a particular string, type C-r. Typing C-s searches forward through the history. The characters present in the value of the isearch-terminators variable are used to terminate an incremental search. If that variable has not been assigned a value, the (W) and C-J characters will terminate an incremental search. C-g will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the search string becomes the current line. To find other matching entries in the history list, type C-r or C-s as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a Readline command will terminate the search and execute that command. For instance, a MM) will terminate the search and accept the line, thereby executing the command from the history list. A movement command will terminate the search, make the last line found the current line, and begin editing. Readline remembers the last incremental search string. If two C-rs are typed without any intervening characters defining a new search string, any remembered search string is used. Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line. 8.3 Readline Init File Although the Readline library comes with a set of Emacs-like keybindings installed by default, it is possible to use a different set of keybindings. Any user can customize programs that use Readline by putting commands in an inputrc file, conventionally in his home directory. The name of this file is taken from the value of the shell variable INPUTRC. If that variable is unset, the default is 'V. inputre. When a program which uses the Readline library starts up, the ink file is read, and the key bindings are set. In addition, the C-x C-r command re-reads this init file, thus incorporating any changes that you might have made to it. 8.3.1 Readline Init File Syntax There are only a few basic constructs allowed in the Readline init file. Blank lines are ignored. Lines beginning with a 1' are comments. Lines beginning with a `V indicate EFTA00315944

Chapter 8: Command Line Editing 91 conditional constructs (see Section 8.3.2 [Conditional Init Constructs], page 95). Other lines denote variable settings and key bindings. Variable Settings You can modify the run-time behavior of Readline by altering the values of variables in Readline using the set command within the hilt file. The syntax is simple: set variable value Here, for example, is how to change from the default Emacs-like key binding to use vi line editing commands: set editing-mode vi Variable names and values, where appropriate, are recognized without regard to case. Unrecognized variable names are ignored. Boolean variables (those that can be set to on or off) are set to on if the value is null or empty, on (case-insensitive), or 1. Any other value results in the variable being set to off. The bind -V command lists the current Readline variable names and values. See Section 4.2 [Bash Builtins], page 39. A great deal of run-time behavior is changeable with the following variables. bell-style Controls what happens when Readline wants to ring the termi- nal bell. If set to `none', Readline never rings the bell. If set to `visible', Readline uses a visible bell if one is available. If set to `audible' (the default), Readline attempts to ring the terminal's bell. bind-tty-special-chars If set to 'on', Readline attempts to bind the control characters treated specially by the kernel's terminal driver to their Readline equivalents. comment-begin The string to insert at the beginning of the line when the insert- comment command is executed. The default value is "#". completion-ignore-case If set to 'on', Headline performs filename matching and completion in a case-insensitive fashion. The default value is 'off'. completion-query-items The number of possible completions that determines when the user is asked whether the list of possibilities should be displayed. If the number of possible completions is greater than this value, Readline will ask the user whether or not he wishes to view them; otherwise, they are simply listed. This variable must be set to an integer value greater than or equal to 0. A negative value means Readline should never ask. The default limit is 100. EFTA00315945

92 Bash Reference Manual convert -meta If set to 'on', Readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and prefixing an (ESC) character, converting them to a meta-prefixed key sequence. The default value is 'on'. disable-completion If set to 'On', Readline will inhibit word completion. Completion characters will be inserted into the line as if they had been mapped to self -insert. The default is 'off'. editing-mode The editing-mode variable controls which default set of key bind- ings is used. By default, Readline starts up in Emacs editing mode, where the keystrokes are most similar to Emacs. This variable can be set to either 'emacs' or 'vi'. enable-keypad When set to 'on', Readline will try to enable the application keypad when it is called. Some systems need this to enable the arrow keys. The default is 'off'. expand-tilde If set to 'on', tilde expansion is performed when Readline attempts word completion. The default is 'off'. history-preserve-point If set to 'on', the history code attempts to place point at the same location on each history line retrieved with previous-history or next-history. The default is 'off'. horizontal-scroll-mode This variable can be set to either 'on' or 'off'. Setting it to 'on' means that the text of the lines being edited will scroll horizontally on a single screen line when they are longer than the width of the screen, instead of wrapping onto a new screen line. By default, this variable is set to 'off'. input-meta If set to 'on', Readline will enable eight-bit input (it will not clear the eighth bit in the characters it reads), regardless of what the terminal claims it can support. The default value is 'off'. The name meta-flag is a synonym for this variable. isearch-terminators The string of characters that should terminate an incremental search without subsequently executing the character as a command (see Section 8.2.5 [Searching], page 90). If this variable has not been given a value, the characters eS j and C-J will terminate an incremental search. keymap Sets Readline's idea of the current keymap for key binding com- mands. Acceptable keymap names are emacs, emacs-standard, EFTA00315946

Chapter 8: Command Line Editing 93 emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. The default value is emacs. The value of the editing-mode variable also affects the default keymap. mark-directories If set to `on', completed directory names have a slash appended. The default is `on'. mark-modified-lines This variable, when set to `on', causes Readline to display an as- terisk (`•') at the start of history lines which have been modified. This variable is `off' by default. mark-symlinked-directories If set to `on', completed names which are symbolic links to di- rectories have a slash appended (subject to the value of mark- directories). The default is `off'. match-hidden-files This variable, when set to 'on', causes Readline to match files whose names begin with a .' (hidden files) when performing filename completion, unless the leading 1. 1 is supplied by the user in the filename to be completed. This variable is 'on' by default. output-meta If set to `on', Readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence. The default is `off'. page-completions If set to 'on', Readline uses an internal more-like pager to display a screenful of possible completions at a time. This variable is 'on' by default. print -complet ions-horizontally If set to `on', Readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen. The default is `off'. show-all -if -ambiguous This alters the default behavior of the completion functions. If set to `on', words which have more than one possible completion cause the matches to be listed immediately instead of ringing the bell. The default value is `off'. show-all -if -unmodif ied This alters the default behavior of the completion functions in a fashion similar to show-all-if-ambiguous. If set to `on', words which have more than one possible completion without any possible par- tial completion (the possible completions don't share a common prefix) cause the matches to be listed immediately instead of ring- ing the bell. The default value is `off'. EFTA00315947

94 Bash Reference Manual visible-stats If set to 'on', a character denoting a file's type is appended to the filename when listing possible completions. The default is `off'. Key Bindings The syntax for controlling key bindings in the init file is simple. First you need to find the name of the command that you want to change. The following sections contain tables of the command name, the default keybinding, if any, and a short description of what the command does. Once you know the name of the command, simply place on a line in the init file the name of the key you wish to bind the command to, a colon, and then the name of the command. The name of the key can be expressed in different ways, depending on what you find most comfortable. In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro). The bind -p command displays Readline function names and bindings in a format that can put directly into an initialization file. See Section 4.2 [Bash Builtins], page 39. keyname: function-name or macro keyname is the name of a key spelled out in English. For example: Control-u: universal-argument Meta-Rubout: backward-kill-word Control-o: "> output" In the above example, C-u is bound to the function universal- argument, If-DEL is bound to the function backward-kill-word, and C-o is bound to run the macro expressed on the right hand side (that is, to insert the text `> output' into the line). A number of symbolic character names are recognized while pro- cessing this key binding syntax: DEL, ESC, ESCAPE, LFD, NEW- LINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB. "keyseq": function-name or macro keyseq differs from keyname above in that strings denoting an en- tire key sequence can be specified, by placing the key sequence in double quotes. Some GNU Emacs style key escapes can be used, as in the following example, but the special character names are not recognized. "\C-u": universal-argument "\C-x\C-r": re-read-init-file " Ill"": "Function Key 1" In the above example, C-u is again bound to the function universal-argument (just as it was in the first example), `C-x C-r' is bound to the function re-read-init-file, and `(ff0) @ C) Cr is bound to insert the text `Function Key 1'. The following GNU Emacs style escape sequences are available when specifying key sequences: EFTA00315948