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9.1 Bash History Facilities

When the -o history option to the set builtin is enabled (see The Set Builtin), the shell provides access to the command history, the list of commands previously typed. The value of the HISTSIZE shell variable is used as the number of commands to save in a history list. The text of the last $HISTSIZE commands (default 500) is saved. The shell stores each command in the history list prior to parameter and variable expansion but after history expansion is performed, subject to the values of the shell variables HISTIGNORE and HISTCONTROL.

When the shell starts up, the history is initialized from the file named by the HISTFILE variable (default ~/.bash_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 the HISTFILESIZE variable. When a shell with history enabled exits, the last $HISTSIZE lines are copied from the history list to the file named by $HISTFILE. If the histappend shell option is set (see Bash Builtin Commands), the lines are appended to the history file, otherwise the history file is overwritten. If HISTFILE is unset, or if the history file 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 unset, or set to null, a non-numeric value, or a numeric value less than zero, the history file is not truncated.

If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is written to the history file, marked with the history comment character. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps for the following history entry.

The builtin command fc may be used to list or edit and re-execute a portion of the history list. The history builtin may be used to display or modify the history list and manipulate the history file. When using command-line editing, search commands are available in each editing mode that provide access to the history list (see Commands For Manipulating The History).

The shell allows control over which commands are saved on the history list. The HISTCONTROL and HISTIGNORE variables may be set to cause the shell to save only a subset of the commands entered. The cmdhist shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve syntactic correctness. The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons. The shopt builtin is used to set these options. See The Shopt Builtin, for a description of shopt.

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