/usr/bin/bash: Difference between revisions

When the -o history option to the set builtin is enabled, the shell provides access to  the  command history, the list of commands previously typed.  The value of the HISTSIZE 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 (see EXPANSION above) but after history expansion is performed, subject to the values of the shell variables HISTIGNORE and HISTCONTROL.

On  startup,  the  history  is  initialized from the file named by the variable HISTFILE (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 HISTFILESIZE.  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.  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  line. These  timestamps are optionally displayed depending on the value of the HISTTIMEFORMAT variable.

When a shell with history enabled exits, the last $HISTSIZE lines are  copied  from  the  history list to $HISTFILE.  If the histappend shell option is enabled (see the description of shopt under SHELL BUILTIN COMMANDS below), 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.  If the HISTTIMEFORMAT variable is set, time stamps are written to the  history  file, marked  with the history comment character, so they may be preserved across shell sessions.  This uses the history comment character to distinguish timestamps from  other  history  lines.  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.

The builtin command fc (see SHELL BUILTIN COMMANDS below) 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.

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  multiline 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.  See the description of the shopt builtin below under SHELL BUILTIN COMMANDS for information on setting and unsetting shell options.