9.3 History Expansion
The History library provides a history expansion feature that is similar
to the history expansion provided by csh. This section
describes the syntax used to manipulate the history information.
History expansions introduce words from the history list into
the input stream, making it easy to repeat commands, insert the
arguments to a previous command into the current input line, or
fix errors in previous commands quickly.
History expansion takes place in two parts. The first is to determine
which line from the history list should be used during substitution.
The second is to select portions of that line for inclusion into the
current one. The line selected from the history is called the
event, and the portions of that line that are acted upon are
called words. Various modifiers are available to manipulate
the selected words. The line is broken into words in the same fashion
that Bash does, so that several words
surrounded by quotes are considered one word.
History expansions are introduced by the appearance of the
history expansion character, which is '!' by default.
Only '\' and ''' may be used to escape the history expansion
character.
Several shell options settable with the shopt
builtin (see section 4.2 Bash Builtin Commands) may be used to tailor
the behavior of history expansion. If the
histverify shell option is enabled, and Readline
is being used, history substitutions are not immediately passed to
the shell parser.
Instead, the expanded line is reloaded into the Readline
editing buffer for further modification.
If Readline is being used, and the histreedit
shell option is enabled, a failed history expansion will be
reloaded into the Readline editing buffer for correction.
The -p option to the history builtin command
may be used to see what a history expansion will do before using it.
The -s option to the history builtin may be used to
add commands to the end of the history list without actually executing
them, so that they are available for subsequent recall.
This is most useful in conjunction with Readline.
The shell allows control of the various characters used by the
history expansion mechanism with the histchars variable.
