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This document describes the GNU History library, a programming tool that provides a consistent user interface for recalling lines of previously typed input.

Published by the Free Software Foundation
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Cambridge, MA 02139 USA

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 copy and distribute modified versions of this manual under the conditions for verbatim copying, 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, except that this permission notice may be stated in a translation approved by the Foundation.

Copyright (C) 1989, 1991 Free Software Foundation, Inc.

# 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 your own programs, see section Programming with GNU History.

- History Interaction: What it feels like using History as a user.

## History Interaction

The History library provides a history expansion feature that is similar to the history expansion provided by `csh`. The following text describes the syntax used to manipulate the history information.

History expansion takes place in two parts. The first is to determine which line from the previous history 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 previous history is called the event, and the portions of that line that are acted upon are called words. The line is broken into words in the same fashion that Bash does, so that several English (or Unix) words surrounded by quotes are considered as one word.

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

### 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 `(`.
`!!`
  Refer to the previous command. This is a synonym for `!-1`.
`!n`
  Refer to command line n.
`!-n`
  Refer to the command n lines back.
`!string`
  Refer to the most recent command starting with string.
`!?string`[`?`]
  Refer to the most recent command containing string.
`!#`
  The entire command line typed so far.
`^string1^string2^`
  Quick Substitution. Repeat the last command, replacing string1 with string2. Equivalent to `!!:s/string1/string2/`.

### Word Designators

A `:` separates the event specification from the word designator. It can 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 a 0 (zero).

`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.

### 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.
`r`
  Remove a trailing suffix of the form ``.'`suffix, leaving the basename.
`e`
  Remove all but the trailing suffix.
`t`
  Remove all leading pathname components, leaving the tail.
`p`
  Print the new command but do not execute it.
`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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