Bash Reference Manual - 7. Using History Interactively

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# 7. Using History Interactively

This chapter describes how to use the GNU History Library interactively, from a user's standpoint. It should be considered a user's guide. For information on using the GNU History Library in other programs, see the GNU Readline Library Manual.

## 7.1 Bash History Facilities

When the ``-o history'` option to the `set` builtin is enabled (see section 5.5 The Set Builtin), the shell provides access to the command history, the list of commands previously typed. The text of the last `HISTSIZE` commands (default 500) is saved in a history list. 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'`). `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 `HISTFILE`. If the `histappend` shell option is set (see section 5.4 Bash Builtin Commands), 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.

The builtin command `fc` may be used to list or edit and re-execute a portion of the history list. The `history` builtin can be used to display or modify the history list and manipulate the history file. When using the 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 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. See section 5.4 Bash Builtin Commands, for a description of `shopt`.

## 7.2 Bash History Builtins

Bash provides two builtin commands that allow you to manipulate the history list and history file.

`fc`

      fc [-e ename] [-nlr] [first] [last]
      fc -s [pat=rep] [command]

  Fix Command. In the first form, a range of commands from first to last is selected from the history list. Both first and 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). If last is not specified it is set to first. If first is not specified it is set to the previous command for editing and -16 for listing. If the ``-l'` flag is given, the commands are listed on standard output. The ``-n'` flag suppresses the command numbers when listing. The ``-r'` flag reverses the order of the listing. Otherwise, the editor given by ename is invoked on a file containing those commands. If ename is not given, the value of the following variable expansion is used: `${FCEDIT:-${EDITOR:-vi}}`. This says to use the value of the `FCEDIT` variable if set, or the value of the `EDITOR` variable if that is set, or `vi` if neither is set. When editing is complete, the edited commands are echoed and executed. In the second form, command is re-executed after each instance of pat in the selected command is replaced by rep. A useful alias to use with the `fc` command is `r='fc -s'`, so that typing ``r cc'` runs the last command beginning with `cc` and typing ``r'` re-executes the last command (see section 5.9 Aliases).
`history`

      history [-c] [n]
      history [-anrw] [filename]
      history -ps arg

  Display the history list with line numbers. Lines prefixed with with a ``*'` have been modified. An argument of n says to list only the last n lines. Options, if supplied, have the following meanings:
  `-w`
    Write out the current history to the history file.
  `-r`
    Read the current history file and append its contents to the history list.
  `-a`
    Append the new history lines (history lines entered since the beginning of the current Bash session) to the history file.
  `-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.
  `-c`
    Clear the history list. This may be combined with the other options to replace the history list completely.
  `-s`
    The args are added to the end of the history list as a single entry.
  `-p`
    Perform history substitution on the args and display the result on the standard output, without storing the results in the history list.
  When the ``-w'`, ``-r'`, ``-a'`, or ``-n'` option is used, if filename is given, then it is used as the history file. If not, then the value of the `HISTFILE` variable is used.

## 7.3 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 5.4 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.

### 7.3.1 Event Designators

An event designator is a reference to a command line entry in the history list.

`!`
  Start a history substitution, except when followed by a space, tab, the end of the line, ``='` or ``('`.
`!n`
  Refer to command line n.
`!-n`
  Refer to the command n lines back.
`!!`
  Refer to the previous command. This is a synonym for ``!-1'`.
`!string`
  Refer to the most recent command starting with string.
`!?string[?]`
  Refer to the most recent command containing string. The trailing ``?'` may be omitted if the string is followed immediately by a newline.
`^string1^string2^`
  Quick Substitution. Repeat the last command, replacing string1 with string2. Equivalent to `!!:s/string1/string2/`.
`!#`
  The entire command line typed so far.

### 7.3.2 Word Designators

Word designators are used to select desired words from the event. A ``:'` separates the event specification from the word designator. It may be omitted if the word designator begins with a ``^'`, ``$'`, ``*'`, ``-'`, or ``%'`. 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.

`0 (zero)`
  The `0`th word. For many applications, this is the command word.
`n`
  The nth word.
`^`
  The first argument; that is, word 1.
`$`
  The last argument.
`%`
  The word matched by the most recent ``?string?'` search.
`x-y`
  A range of words; ``-y'` abbreviates ``0-y'`.
`*`
  All of the words, except the `0`th. This is a synonym for ``1-$'`. It is not an error to use ``*'` if there is just one word in the event; the empty string is returned in that case.
`x*`
  Abbreviates ``x-$'`
`x-`
  Abbreviates ``x-$'` like ``x*'`, but omits the last word.

If a word designator is supplied without an event specification, the previous command is used as the event.

### 7.3.3 Modifiers

After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a ``:'`.

`h`
  Remove a trailing pathname component, leaving only the head.
`t`
  Remove all leading pathname components, leaving the tail.
`r`
  Remove a trailing suffix of the form ``.suffix'`, leaving the basename.
`e`
  Remove all but the trailing suffix.
`p`
  Print the new command but do not execute it.
`q`
  Quote the substituted words, escaping further substitutions.
`x`
  Quote the substituted words as with ``q'`, but break into words at spaces, tabs, and newlines.
`s/old/new/`
  Substitute new for the first occurrence of old in the event line. Any delimiter may be used in place of ``/'`. The delimiter may be quoted in old and new with a single backslash. If ``&'` appears in new, it is replaced by old. A single backslash will quote the ``&'`. The final delimiter is optional if it is the last character on the input line.
`&`
  Repeat the previous substitution.
`g`
  Cause changes to be applied over the entire event line. Used in conjunction with ``s'`, as in `gs/old/new/`, or with ``&'`.

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