history). The file named by the value of HISTFILE is truncated, if necessary. to contain no more than the number of lines specified by the value of HISTFILESIZE. When an interactive shell exits, the last SHISTSIZE lines are copied from the history list to SHISTFILE. If the histappend shell option is enabled

le is unwritable, the history is not saved. After saving the history, the history file is truncated to contain no more than $HISTFILESIZE lines. If HISTFILESIZE is not set, no truncation is performed. If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is written to t