bashrefes/hsuser.texi

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

Copyright (C) 1988--2020 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 text of the last @env{$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
@env{HISTIGNORE} and @env{HISTCONTROL}.

When the shell starts up, the history is initialized from the
file named by the @env{HISTFILE} variable (default @file{~/.bash_history}).
The file named by the value of @env{HISTFILE} is truncated, if
necessary, to contain no more than the number of lines specified by
the value of the @env{HISTFILESIZE} variable.
When a shell with history enabled exits, the last
@env{$HISTSIZE} lines are copied from the history list to the file
named by @env{$HISTFILE}.
If the @code{histappend} shell option is set (@pxref{Bash Builtins}),
the lines are appended to the history file,
otherwise the history file is overwritten.
If @env{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 @env{$HISTFILESIZE} lines.
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.

If the @env{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 @code{fc} may be used to list or edit and re-execute
a portion of the history list.
The @code{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 (@pxref{Commands For History}).

The shell allows control over which commands are saved on the history
list.  The @env{HISTCONTROL} and @env{HISTIGNORE}
variables may be set to cause the shell to save only a subset of the
commands entered.
The @code{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 @code{lithist}
shell option causes the shell to save 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
@var{first}.  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
given, 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, the editor given by
@var{ename} is invoked on a file containing those commands.  If
@var{ename} is not given, the value of the following variable expansion
is used: @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, the edited commands are echoed and executed.

In the second form, @var{command} is re-executed after each instance
of @var{pat} in the selected command is replaced by @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}).

@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 line numbers.
Lines prefixed with a @samp{*} have been modified.
An argument of @var{n} lists only the last @var{n} lines.
If the shell variable @env{HISTTIMEFORMAT} is set and not null,
it is used as a format string for @var{strftime} to display
the time stamp associated with each displayed history entry.
No intervening blank is printed between the formatted time stamp
and the history line.

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 completely.

@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 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
Append the history lines not already read from the history file
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 out the current history list to 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
The @var{arg}s are added to the end of
the history list as a single entry.

@end table

When any of the @option{-w}, @option{-r}, @option{-a}, or @option{-n} options is
used, if @var{filename}
is given, then it is used as the history file.  If not, then
the value of the @env{HISTFILE} variable is used.

@end table
@end ifset

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

The History library provides a history expansion feature that is similar
to the history expansion provided by @code{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.

@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 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
@dfn{event}, and the portions of that line that are acted upon are
called @dfn{words}.  Various @dfn{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 @samp{!} by default.

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. 
@end ifset

@ifset BashFeatures
Several shell options settable with the @code{shopt}
builtin (@pxref{The Shopt Builtin}) may be used to tailor
the behavior of history expansion.  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 will be
reloaded into the Readline editing buffer for correction.
The @option{-p} option to the @code{history} builtin command
may be used to see 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 a command line entry in the
history list.
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 @samp{(} (when the
@code{extglob} shell option is enabled using the @code{shopt} builtin).
@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 command line @var{n}.

@item @code{!-@var{n}}
Refer to the command @var{n} lines back.

@item @code{!!}
Refer to the previous command.  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, the string from the most recent search is used;
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.
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).  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 argument 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 many applications, this is the command word.

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

@item ^
The first argument; that is, word 1.

@item $
The last argument.

@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.

@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;
the empty string is returned 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.

@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 pathname component, leaving only the head.

@item t
Remove all leading pathname 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; the last one
supplied is used.
@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 by @var{old}.  A single backslash will quote
the @samp{&}.
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 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.  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