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 an interactive shell 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 Builtins),
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 not set, no truncation is performed.
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 previous history line.
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 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 Bash Builtins, for a description of shopt.