GNU Readline

Last updated
GNU Readline
Original author(s) Brian Fox
Developer(s) Chet Ramey
Initial release1989;36 years ago (1989)
Stable release
8.2 [1]   OOjs UI icon edit-ltr-progressive.svg / 26 September 2022
Preview release
8.3-alpha [2]   OOjs UI icon edit-ltr-progressive.svg / 22 April 2024
Repository
Written in C
Type Library
License 2009: GPL-3.0-or-later [a]
1997: GPL-2.0-or-later [b]
1994: GPL-1.0-or-later [c]
Website www.gnu.org/software/readline/   OOjs UI icon edit-ltr-progressive.svg

GNU Readline is a software library that provides in-line editing and history capabilities for interactive programs with a command-line interface, such as Bash. It is currently maintained by Chet Ramey as part of the GNU Project.

Contents

It allows users to move the text cursor, search the command history, control a kill ring (a more flexible version of a copy/paste clipboard) and use tab completion on a text terminal. As a cross-platform library, readline allows applications on various systems to exhibit identical line-editing behavior.

Editing modes

Readline supports both Emacs and vi editing modes, which determine how keyboard input is interpreted as editor commands. See Editor war § Comparison.

Emacs keyboard shortcuts

Emacs editing mode key bindings are taken from the text editor Emacs.

On some systems, Esc must be used instead of Alt, because the Alt shortcut conflicts with another shortcut. For example, pressing Alt+f in Xfce's terminal emulator window does not move the cursor forward one word, but activates "File" in the menu of the terminal window, unless that is disabled in the emulator's settings.

Choice of the GPL as GNU Readline's license

GNU Readline is notable for being a free software library which is licensed under the GNU General Public License (GPL). Free software libraries are far more often licensed under the GNU Lesser General Public License (LGPL), for example, the GNU C Library, GNU gettext and FLTK. A developer of an application who chooses to link to an LGPLv3 licensed library can use any license that does not: "restrict modification of the portions of the Library contained in the Combined Work and reverse engineering for debugging such modifications". [4] But linking to a GPLv3 licensed library such as Readline requires the entire combined resulting application to be licensed under the GPLv3 when distributed, to comply with section 5 of the GPL. [5] [6]

This licensing was chosen by the FSF on the hopes that it would encourage software to switch to the GPL. [7] An important example of an application changing its licensing to comply with the copyleft conditions of GNU Readline is CLISP, an implementation of Common Lisp. Originally released in 1987, it changed to the GPL license in 1992, [8] after an email exchange between one of CLISP's original authors, Bruno Haible, and Richard Stallman, in which Stallman argued [9] that the linking of readline in CLISP meant that Haible was required to re-license CLISP under the GPL if he wished to distribute the implementation of CLISP which used readline. [10]

Another response has been to not use this in some projects, making text input use the primitive Unix terminal driver for editing.

Alternative libraries

Alternative libraries have been created with other licenses so they can be used by software projects which want to implement command line editing functionality, but be released with a non-GPL license.

Sample code

The following code is in C and must be linked against the readline library by passing a -lreadline flag to the compiler:

#include<stdlib.h>#include<stdio.h>#include<readline/readline.h>#include<readline/history.h>intmain(){// Configure readline to auto-complete paths when the tab key is hit.rl_bind_key('\t',rl_complete);// Enable historyusing_history();while(1){// Display prompt and read inputchar*input=readline("prompt> ");// Check for EOF.if(!input)break;// Add input to readline history.add_history(input);// Do stuff...// Free buffer that was allocated by readlinefree(input);}return0;}

Bindings

Non-C programming languages that provide language bindings for readline include

Support for readline alternatives differ among these bindings.

Notes

  1. ↑ GPL-3.0-or-later since version 6.0 (2009-02-20).
  2. ↑ GPL-2.0-or-later from version 2.1 (1997-06-05) until version 5.2 (2006-10-11).
  3. ↑ GPL-1.0-or-later from ? until version 2.0 (1994-08-04).
  4. ↑ A part of pseudoterminals or PTYs (for Linux), which is evident from the terminal configuration tools such as stty; in typical Linux distribution the PTY master endpoint treats special characters as signals to be sent to slaves e.g.SIGINT [3]

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References

  1. ↑ Chet Ramey (26 September 2022). "Readline-8.2 Release available" . Retrieved 26 September 2022.
  2. ↑ "readline.git - The GNU Readline library" . Retrieved 7 August 2024.
  3. ↑ "pty(7) - Linux manual page". man7.org. Retrieved 2021-09-30.
  4. ↑ "GNU Lesser General Public License". The GNU Lesser General Public License v3.0 - GNU Project. Free Software Foundation. 2007. Retrieved 2011-09-03.
  5. ↑ "GNU General Public License". The GNU General Public License v3.0 - GNU Project. Free Software Foundation. 2007. Retrieved 2011-09-03.
  6. ↑ "Frequently Asked Questions about the GNU licenses". Frequently Asked Questions about the GNU Licenses - GNU Project. Free Software Foundation. 2010. Retrieved 2011-09-03.
  7. ↑ "Why you shouldn't use the Lesser GPL for your next library". Why you shouldn't use the Lesser GPL for your next library - GNU Project - Free Software Foundation. Free Software Foundation. 2016. Retrieved 2019-10-15.
  8. ↑ "CLISP copyright notice". CLISP repository. 1992. Retrieved 2011-09-03.
  9. ↑ "Why CLISP is under GPL". CLISP repository. 1992. Retrieved 2023-01-19.
  10. ↑ "License - why GNU GPL?". Frequently Asked Questions (With Answers) about CLISP. CLISP team. Retrieved 2011-09-03.
  11. ↑ "editline(3) - NetBSD Manual Pages". NetBSD . Retrieved 2022-09-13. Command Line Editor Library (libedit, -ledit)
  12. ↑ Editline Library (libedit)
  13. ↑ "MariaDB/server/blob/10.2/BUILD/SETUP.sh". MariaDB repository. MariaDB Foundation. Retrieved 2017-10-24.
  14. ↑ "php/php-src/tree/master/ext/readline". PHP repository. The PHP Group. Retrieved 2017-10-24.
  15. ↑ Sanfilippo, Salvatore (10 May 2020). "antirez/linenoise". GitHub .
  16. ↑ "Applications and libraries". Haskell wiki. haskell.org. Retrieved 2017-10-24.
  17. ↑ Judah Jacobson. "judah/haskeline: A Haskell library for line input in command-line programs". Haskeline repository. Retrieved 2017-10-24.
  18. ↑ "PowerShell/PSReadLine: A bash inspired readline implementation for PowerShell". PSReadLine repository. Retrieved 2023-12-20.
  19. ↑ "Module: Readline (Ruby 3.0.2)".
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