@ignore
This file documents the user interface to the GNU History library.

Copyright (C) 1988--2025 Free Software Foundation, Inc.
Authored by Brian Fox and Chet Ramey.

Permission is granted to make and distribute verbatim copies of this manual
provided the copyright notice and this permission notice are preserved on
all copies.

Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission notice
identical to this one except for the removal of this paragraph (this
paragraph not being relevant to the printed manual).

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
GNU Copyright statement is available to the distributee, and provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions.
@end ignore

@node Using History Interactively
@chapter Using History Interactively

@ifclear BashFeatures
@defcodeindex bt
@end ifclear

@ifset BashFeatures
This chapter describes how to use the @sc{gnu} History Library
interactively, from a user's standpoint.
It should be considered a user's guide.
For information on using the @sc{gnu} History Library in other programs,
see the @sc{gnu} Readline Library Manual.
@end ifset
@ifclear BashFeatures
This chapter describes how to use the @sc{gnu} History Library
interactively, from a user's standpoint.
It should be considered a user's guide.
For information on using the @sc{gnu} History Library in your own programs,
@pxref{Programming with GNU History}.
@end ifclear

@ifset BashFeatures
@menu
* Bash History Facilities::	How Bash lets you manipulate your command
				history.
* Bash History Builtins::	The Bash builtin commands that manipulate
				the command history.
* History Interaction::		What it feels like using History as a user.
@end menu
@end ifset
@ifclear BashFeatures
@menu
* History Interaction::		What it feels like using History as a user.
@end menu
@end ifclear

@ifset BashFeatures
@node Bash History Facilities
@section Bash History Facilities
@cindex command history
@cindex history list

When the @option{-o history} option to the @code{set} builtin
is enabled (@pxref{The Set Builtin}),
the shell provides access to the @dfn{command history},
the list of commands previously typed.
The value of the @env{HISTSIZE} shell variable is used as the
number of commands to save in a history list:
the shell saves the text of the last @env{$HISTSIZE}
commands (default 500).
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
@env{HISTIGNORE} and @env{HISTCONTROL}.

When the shell starts up, Bash initializes the history list
by reading history entries from the
file named by the @env{HISTFILE} variable (default @file{~/.bash_history}).
This is referred to as the @dfn{history file}.
The history file is truncated, if necessary,
to contain no more than the number of history entries
specified by the value of the @env{HISTFILESIZE} variable.
If @env{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 entry.
These timestamps are optionally displayed depending on the value of the
@env{HISTTIMEFORMAT} variable (@pxref{Bash Variables}).
When present, history timestamps delimit history entries, making
multi-line entries possible.

When a shell with history enabled exits, Bash copies the last
@env{$HISTSIZE} entries from the history list to the file
named by @env{$HISTFILE}.
If the @code{histappend} shell option is set (@pxref{Bash Builtins}),
Bash appends the entries to the history file,
otherwise it overwrites the history file.
If @env{HISTFILE} is unset or null,
or if the history file is unwritable, the history is not saved.
After saving the history, Bash truncates the history file
to contain no more than @env{$HISTFILESIZE}
lines as described above.

If the @env{HISTTIMEFORMAT}
variable is set, the shell writes the timestamp information
associated with each history entry to the history file,
marked with the history comment character,
so timestamps are preserved across shell sessions.
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.
As above, when using @env{HISTTIMEFORMAT},
the timestamps delimit multi-line history entries.

The @code{fc} builtin command will list or edit and re-execute a
portion of the history list.
The @code{history} builtin can 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 (@pxref{Commands For History}). 

The shell allows control over which commands are saved on the history list. 
The @env{HISTCONTROL} and @env{HISTIGNORE}
variables are used to save only a subset of the commands entered.
If the @code{cmdhist} shell option is
enabled, the shell attempts to save each
line of a multi-line command in the same history entry, adding
semicolons where necessary to preserve syntactic correctness.
The @code{lithist}
shell option modifies @code{cmdhist} by saving
the command with embedded newlines instead of semicolons.
The @code{shopt} builtin is used to set these options.
@xref{The Shopt Builtin}, for a description of @code{shopt}.

@node Bash History Builtins
@section Bash History Builtins
@cindex history builtins

Bash provides two builtin commands which manipulate the
history list and history file.

@table @code

@item fc
@btindex fc
@example
@code{fc [-e @var{ename}] [-lnr] [@var{first}] [@var{last}]}
@code{fc -s [@var{pat}=@var{rep}] [@var{command}]}
@end example

The first form selects a range of commands from
@var{first} to @var{last}
from the history list and displays or edits and re-executes them.
Both @var{first} and
@var{last} may be specified as a string (to locate the most recent
command beginning with that string) or as a number (an index into the
history list, where a negative number is used as an offset from the
current command number).

When listing, a @var{first} or @var{last} of 0 is equivalent to -1
and -0 is equivalent to the current command (usually the @code{fc}
command);
otherwise 0 is equivalent to -1 and -0 is invalid.

If @var{last} is not specified, it is set to
the current command for listing and to @var{first} otherwise.
If @var{first} is not specified, it is set to the previous
command for editing and @minus{}16 for listing.

If the @option{-l} flag is supplied,
the commands are listed on standard output.
The @option{-n} flag suppresses the command numbers when listing.
The @option{-r} flag reverses the order of the listing.

Otherwise, @code{fc} invokes the editor named by
@var{ename} on a file containing those commands.
If @var{ename} is not supplied, @code{fc} uses the value of the following
variable expansion: @code{$@{FCEDIT:-$@{EDITOR:-vi@}@}}.
This says to use the
value of the @env{FCEDIT} variable if set, or the value of the
@env{EDITOR} variable if that is set, or @code{vi} if neither is set.
When editing is complete, @code{fc} reads the file of edited commands
and echoes and executes them.

In the second form, @code{fc} re-executes @var{command} after
replacing each instance of @var{pat} in the selected command with @var{rep}.
@var{command} is interpreted the same as @var{first} above.

A useful alias to use with the @code{fc} command is @code{r='fc -s'}, so
that typing @samp{r cc} runs the last command beginning with @code{cc}
and typing @samp{r} re-executes the last command (@pxref{Aliases}).

If the first form is used, the return value is zero unless an invalid
option is encountered or @var{first} or @var{last}
specify history lines out of range.
When editing and re-executing a file of commands,
the return value is the value of the last command executed
or failure if an error occurs with the temporary file.
If the second form is used, the return status
is that of the re-executed command, unless
@var{command} does not specify a valid history entry, in which case
@code{fc} returns a non-zero status.

@item history
@btindex history
@example
history [@var{n}]
history -c
history -d @var{offset}
history -d @var{start}-@var{end}
history [-anrw] [@var{filename}]
history -ps @var{arg}
@end example

With no options, display the history list with numbers.
Entries prefixed with a @samp{*} have been modified.
An argument of @var{n} lists only the last @var{n} entries.
If the shell variable @env{HISTTIMEFORMAT} is set and not null,
it is used as a format string for @code{strftime}(3) to display
the time stamp associated with each displayed history entry.
If @code{history} uses @env{HISTTIMEFORMAT}, it does not print an
intervening space between the formatted time stamp and the history entry.

Options, if supplied, have the following meanings:

@table @code
@item -c
Clear the history list.
This may be combined with the other options to replace the history list.

@item -d @var{offset}
Delete the history entry at position @var{offset}.
If @var{offset} is positive, it should be specified as it appears when
the history is displayed.
If @var{offset} is negative, it is interpreted as relative to one greater
than the last history position, so negative indices count back from the
end of the history, and an index of @samp{-1} refers to the current
@code{history -d} command.

@item -d @var{start}-@var{end}
Delete the range of history entries between positions @var{start} and
@var{end}, inclusive.
Positive and negative values for @var{start} and @var{end}
are interpreted as described above.

@item -a
Append the "new" history lines to the history file.
These are history lines entered since the beginning of the current
Bash session, but not already appended to the history file.

@item -n
Read the history lines not already read from the history file
and add them to the current history list.
These are lines appended to the history
file since the beginning of the current Bash session.

@item -r
Read the history file and append its contents to the history list.

@item -w
Write the current history list to the history file, overwriting
the history file.

@item -p
Perform history substitution on the @var{arg}s and display the result
on the standard output, without storing the results in the history list.

@item -s
Add the @var{arg}s to the end of the history list as a single entry.
The last command in the history list is removed before adding the @var{arg}s.

@end table

If a @var{filename} argument is supplied
with any of the @option{-w}, @option{-r}, @option{-a}, or @option{-n}
options, Bash uses @var{filename} as the history file.
If not, it uses the value of the @env{HISTFILE} variable.
If @env{HISTFILE} is unset or null, these options have no effect.

If the @env{HISTTIMEFORMAT}
variable is set, @code{history} writes the time stamp information
associated with each history entry to the history file,  
marked with the history comment character as described above.
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 return value is 0 unless an invalid option is encountered, an
error occurs while reading or writing the history file, an invalid
@var{offset} or range is supplied as an argument to @option{-d}, or the
history expansion supplied as an argument to @option{-p} fails.

@end table
@end ifset

@node History Interaction
@section History Expansion
@cindex history expansion

@ifset BashFeatures
The shell
@end ifset
@ifclear BashFeatures
The History library
@end ifclear
provides a history expansion feature that is similar
to the history expansion provided by @code{csh}
(also referred to as history substitution where appropriate).
This section describes the syntax used to manipulate the
history information.

@ifset BashFeatures
History expansion is enabled by default for interactive shells,
and can be disabled using the @option{+H} option to the @code{set}
builtin command (@pxref{The Set Builtin}).
Non-interactive shells do not perform history expansion by default,
but it can be enabled with @code{set -H}.
@end ifset

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.

@ifset BashFeatures
History expansion is performed immediately after a complete line
is read, before the shell breaks it into words, and is performed
on each line individually.
Bash attempts to inform the history
expansion functions about quoting still in effect from previous lines.
@end ifset

History expansion takes place in two parts.
The first is to determine
which entry from the history list should be used during substitution.
The second is to select portions of that entry to include into the
current one.

The entry selected from the history is called the @dfn{event},
and the portions of that entry that are acted upon are @dfn{words}.
Various @dfn{modifiers} are available to manipulate the selected words.
The entry is split into words in the same fashion that Bash
does when reading input,
so that several words surrounded by quotes are considered one word.
The @dfn{event designator} selects the event, the optional
@dfn{word designator} selects words from the event, and
various optional @dfn{modifiers} are available to manipulate the
selected words.

History expansions are introduced by the appearance of the
history expansion character, which is @samp{!} by default.
History expansions may appear anywhere in the input, but do not nest.

History expansion implements shell-like quoting conventions:
a backslash can be used to remove the special handling for the next character;
single quotes enclose verbatim sequences of characters, and can be used to
inhibit history expansion;
and characters enclosed within double quotes may be subject to history
expansion, since backslash can escape the history expansion character,
but single quotes may not, since they are not treated specially within
double quotes.

@ifset BashFeatures
When using the shell, only @samp{\} and @samp{'} may be used to escape the
history expansion character, but the history expansion character is
also treated as quoted if it immediately precedes the closing double quote
in a double-quoted string. 

Several characters inhibit history expansion if found immediately
following the history expansion character, even if it is unquoted:
space, tab, newline, carriage return, @samp{=},
and the other shell metacharacters.
@end ifset

There is a special abbreviation for substitution, active when the
@var{quick substitution} character
@ifset BashFeatures
(described above under @code{histchars})
@end ifset
@ifclear BashFeatures
(default @samp{^})
@end ifclear
is the first character on the line.
It selects the previous history list entry, using an event designator
equivalent to @code{!!},
and substitutes one string for another in that entry.
It is described below (@pxref{Event Designators}).
This is the only history expansion that does not begin with the history
expansion character.

@ifset BashFeatures
Several shell options settable with the @code{shopt}
builtin (@pxref{The Shopt Builtin})
modify history expansion behavior
If the @code{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 @code{histreedit}
shell option is enabled, a failed history expansion is
reloaded into the Readline editing buffer for correction.

The @option{-p} option to the @code{history} builtin command
shows what a history expansion will do before using it.
The @option{-s} option to the @code{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 @code{histchars} variable,
as explained above (@pxref{Bash Variables}).
The shell uses the history comment character to mark history
timestamps when writing the history file.
@end ifset

@menu
* Event Designators::	How to specify which history line to use.
* Word Designators::	Specifying which words are of interest.
* Modifiers::		Modifying the results of substitution.
@end menu

@node Event Designators
@subsection Event Designators
@cindex event designators

An event designator is a reference to an entry in the history list.
The event designator consists of the portion of the word beginning
with the history expansion character, and ending with the word designator
if one is present, or the end of the word.
Unless the reference is absolute, events are relative to the current
position in the history list.
@cindex history events

@table @asis

@item @code{!}
@ifset BashFeatures
Start a history substitution, except when followed by a space, tab,
the end of the line, @samp{=},
or the rest of the shell metacharacters defined above
(@pxref{Definitions}).
@end ifset
@ifclear BashFeatures
Start a history substitution, except when followed by a space, tab,
the end of the line, or @samp{=}.
@end ifclear

@item @code{!@var{n}}
Refer to history list entry @var{n}.

@item @code{!-@var{n}}
Refer to the history entry minus @var{n}.

@item @code{!!}
Refer to the previous entry.
This is a synonym for @samp{!-1}.

@item @code{!@var{string}}
Refer to the most recent command
preceding the current position in the history list
starting with @var{string}.

@item @code{!?@var{string}[?]}
Refer to the most recent command
preceding the current position in the history list
containing @var{string}.
The trailing
@samp{?} may be omitted if the @var{string} is followed immediately by
a newline.
If @var{string} is missing, this uses
the string from the most recent search;
it is an error if there is no previous search string.

@item @code{^@var{string1}^@var{string2}^}
Quick Substitution.
Repeat the last command, replacing @var{string1} with @var{string2}.
Equivalent to @code{!!:s^@var{string1}^@var{string2}^}.

@item @code{!#}
The entire command line typed so far.

@end table

@node Word Designators
@subsection Word Designators

Word designators are used to select desired words from the event.
They are optional; if the word designator isn't supplied, the history
expansion uses the entire event.
A @samp{:} separates the event specification from the word designator.
It may be omitted if the word designator begins with a @samp{^}, @samp{$},
@samp{*}, @samp{-}, or @samp{%}.
Words are numbered from the beginning of the line,
with the first word being denoted by 0 (zero).
That first word is usually the command word, and the arguments begin
with the second word.
Words are inserted into the current line separated by single spaces.

@need 0.75
For example,

@table @code
@item !!
designates the preceding command.
When you type this, the preceding command is repeated in toto.

@item !!:$
designates the last word of the preceding command.
This may be shortened to @code{!$}.

@item !fi:2
designates the second argument of the most recent command starting with
the letters @code{fi}.
@end table

@need 0.75
Here are the word designators:

@table @code

@item 0 (zero)
The @code{0}th word.
For the shell, and many other, applications, this is the command word.

@item @var{n}
The @var{n}th word.

@item ^
The first argument: word 1.

@item $
The last word.
This is usually the last argument, but expands to the
zeroth word if there is only one word in the line.

@item %
The first word matched by the most recent @samp{?@var{string}?} search,
if the search string begins with a character that is part of a word.
By default, searches begin at the end of each line and proceed to the
beginning, so the first word matched is the one closest to the end of
the line.

@item @var{x}-@var{y}
A range of words; @samp{-@var{y}} abbreviates @samp{0-@var{y}}.

@item *
All of the words, except the @code{0}th.
This is a synonym for @samp{1-$}.
It is not an error to use @samp{*} if there is just one word in the event;
it expands to the empty string in that case.

@item @var{x}*
Abbreviates @samp{@var{x}-$}.

@item @var{x}-
Abbreviates @samp{@var{x}-$} like @samp{@var{x}*}, but omits the last word.
If @samp{x} is missing, it defaults to 0.

@end table

If a word designator is supplied without an event specification, the
previous command is used as the event, equivalent to @code{!!}. 

@node Modifiers
@subsection Modifiers

After the optional word designator, you can add a sequence of one or more
of the following modifiers, each preceded by a @samp{:}.
These modify, or edit, the word or words selected from the history event.

@table @code

@item h
Remove a trailing filename component, leaving only the head.

@item t
Remove all leading filename components, leaving the tail.

@item r
Remove a trailing suffix of the form @samp{.@var{suffix}}, leaving
the basename.

@item e
Remove all but the trailing suffix.

@item p
Print the new command but do not execute it.

@ifset BashFeatures
@item q
Quote the substituted words, escaping further substitutions.

@item x
Quote the substituted words as with @samp{q},
but break into words at spaces, tabs, and newlines.
The @samp{q} and @samp{x} modifiers are mutually exclusive;
expansion uses the last one supplied.
@end ifset

@item s/@var{old}/@var{new}/
Substitute @var{new} for the first occurrence of @var{old} in the
event line.
Any character may be used as the delimiter in place of @samp{/}.
The delimiter may be quoted in @var{old} and @var{new}
with a single backslash.
If @samp{&} appears in @var{new}, it is replaced with @var{old}.
A single backslash quotes the @samp{&} in @var{old} and @var{new}.
If @var{old} is null, it is set to the last @var{old}
substituted, or, if no previous history substitutions took place,
the last @var{string}
in a !?@var{string}@code{[?]}
search.
If @var{new} is null, each matching @var{old} is deleted.
The final delimiter is optional if it is the last
character on the input line.

@item &
Repeat the previous substitution.

@item g
@itemx a
Cause changes to be applied over the entire event line.
This is used in conjunction with
@samp{s}, as in @code{gs/@var{old}/@var{new}/},
or with @samp{&}.

@item G
Apply the following @samp{s} or @samp{&} modifier once to each word
in the event.

@end table
