bash-completion is a collection of command line command completions for the Bash shell, collection of helper functions to assist in creating new completions, and set of facilities for loading completions automatically on demand, as well as installing them.

The easiest way to install this software is to use a package; refer to Repology for a comprehensive list of operating system distributions, package names, and available versions.

Depending on the package, you may still need to source it from either /etc/bashrc or ~/.bashrc (or any other file sourcing those). If you have only bash >= 4.2 installed, you can do this by simply using:

# Use bash-completion, if available
[[ $PS1 && -f /usr/share/bash-completion/bash_completion ]] && \
    . /usr/share/bash-completion/bash_completion

If you have older bash versions in use, their loading of bash_completion should be prevented. See further for more info.

If you don't have the package readily available for your distribution, or you simply don't want to use one, you can install bash completion using the standard commands for GNU autotools packages:

autoreconf -i  # if not installing from prepared release tarball
./configure
make           # GNU make required
make check     # optional, requires python3 with pytest >= 3.6, pexpect
make install   # as root

These commands install the completions and helpers, as well as a profile.d script that loads bash_completion where appropriate.

If your system does not use the profile.d directory (usually below /etc) mechanism (i.e., does not automatically source shell scripts in it), you can source the $sysconfdir/profile.d/bash_completion.sh script in /etc/bashrc or ~/.bashrc.

The profile.d script provides a configuration file hook that can be used to prevent loading bash_completion on per user basis when it's installed system wide. To do this:

1. Turn off programmable completion with shopt -u progcomp in $XDG_CONFIG_HOME/bash_completion (or ~/.config/bash_completion if $XDG_CONFIG_HOME is not set)
2. Turn it back on (for example in ~/.bashrc) if you want to use programmable completion for other purposes.

If you're using macOS (formerly OS X), /etc/bashrc is apparently not sourced at all. In that case, you can put the bash_completion file in /sw/etc and add the following code to ~/.bash_profile:

if [ -f /sw/etc/bash_completion ]; then
   . /sw/etc/bash_completion
fi

If you find that a given function is producing errors or does not work as it should under certain circumstances when you attempt completion, try running set -x or set -v prior to attempting the completion again. This will produce useful debugging output that will aid us in fixing the problem if you are unable to do so yourself. Turn off the trace output by running either set +x or set +v.

If you are filing an issue, please attach the generated debugging output in set -x mode copy-pasted to a separate, attached file in the report. Before doing so, be sure to review the output for anything you may not want to share in public, and redact as appropriate.

To debug dynamic loading of a completion, tracing needs to be turned on before the debugged completion is attempted the first time. The easiest way to do this is to start a new shell session, and to turn tracing on in it before doing anything else there.

1. Many of the completion functions assume GNU versions of the various text utilities that they call (e.g. grep, sed, and awk). Your mileage may vary.

Q. The bash completion code inhibits some commands from completing on files with extensions that are legitimate in my environment. Do I have to disable completion for that command in order to complete on the files that I need to?

A. No. Use M-/ to (in the words of the bash man page) attempt file name completion on the text to the left of the cursor. This will circumvent any file type restrictions put in place by the bash completion code.

Q. How can I override a completion shipped by bash-completion?

A. Install a local completion of your own appropriately for the desired command, and it will take precedence over the one shipped by us. See the next answer for details where to install it, if you are doing it on per user basis. If you want to do it system wide, you can install eagerly loaded files in compatdir (see a couple of questions further down for more info. To get the path of compatdir for the current system, the output of pkg-config bash-completion --variable compatdir can be used) and install a completion for the commands to override our completion for in them.

If you want to use bash's default completion instead of one of ours, something like this should work (where $cmd is the command to override completion for): complete -o default -o bashdefault $cmd

Q. Where should I install my own local completions?

A. Put them in the completions subdir of $BASH_COMPLETION_USER_DIR (defaults to $XDG_DATA_HOME/bash-completion or ~/.local/share/bash-completion if $XDG_DATA_HOME is not set) to have them loaded automatically on demand when the respective command is being completed. See also the next question's answer for considerations for these files' names, they apply here as well. Alternatively, you can write them directly in ~/.bash_completion which is loaded eagerly by our main script.

Q. I author/maintain package X and would like to maintain my own completion code for this package. Where should I put it to be sure that interactive bash shells will find it and source it?

A. [ Disclaimer: Here, how to make the completion code visible to bash-completion is explained. We do not require always making the completion code visible to bash-completion. In what condition the completion code is installed should be determined at the author/maintainers' own discretion. ]

Install it in one of the directories pointed to by bash-completion's pkgconfig file variables. There are two alternatives:

• The recommended directory is completionsdir, which you can get with pkg-config --variable=completionsdir bash-completion. From this directory, completions are automatically loaded on demand based on invoked commands' names, so be sure to name your completion file accordingly, and to include (for example) symbolic links in case the file provides completions for more than one command. The completion filename for command foo in this directory should be either foo, or foo.bash. (Underscore prefixed _foo works too, but is reserved for bash-completion internal use as a deprecation/fallback marker.)
• The other directory which is only present for backwards compatibility, its usage is no longer recommended, is compatdir (get it with pkg-config --variable=compatdir bash-completion). From this directory, files are loaded eagerly when bash_completion is loaded.

For packages using GNU autotools the installation can be handled for example like this in configure.ac:

PKG_CHECK_VAR(bashcompdir, [bash-completion], [completionsdir], ,
  bashcompdir="${sysconfdir}/bash_completion.d")
AC_SUBST(bashcompdir)

...accompanied by this in Makefile.am:

bashcompdir = @bashcompdir@
dist_bashcomp_DATA = your-completion-file # completion files go here

For cmake we ship the bash-completion-config.cmake and bash-completion-config-version.cmake files. Example usage:

find_package(bash-completion)
if(BASH_COMPLETION_FOUND)
  message(STATUS
    "Using bash completion dir ${BASH_COMPLETION_COMPLETIONSDIR}")
else()
  set (BASH_COMPLETION_COMPLETIONSDIR "/etc/bash_completion.d")
  message (STATUS
    "Using fallback bash completion dir ${BASH_COMPLETION_COMPLETIONSDIR}")
endif()

install(FILES your-completion-file DESTINATION
  ${BASH_COMPLETION_COMPLETIONSDIR})

In bash-completion >= 2.12, we search the data directory of bash-completion under the installation prefix where the target command is installed. When one can assume that the version of the target bash-completion is 2.12 or higher, the completion script can actually be installed to $PREFIX/share/bash-completion/completions/ under the same installation prefix as the target program installed under $PREFIX/bin/ or $PREFIX/sbin/. For the detailed search order, see also "Q. What is the search order for the completion file of each target command?" below.

Example for Makefile.am:

bashcompdir = $(datarootdir)/bash-completion/completions
dist_bashcomp_DATA = your-completion-file

Example for CMakeLists.txt:

install(FILES your-completion-file DESTINATION "${CMAKE_INSTALL_DATAROOTDIR}/bash-completion/completions")

Q. When completing on a symlink to a directory, bash does not append the trailing / and I have to hit <Tab> again. I don't like this.

A. This has nothing to do with bash_completion. It's the default for completing symlinks to directories since bash 2.05a, and was added because sometimes you want to operate on the symlink itself, rather than what it points to.

You can get the pre-2.05a behaviour back by putting set mark-symlinked-directories on in your /etc/inputrc or ~/.inputrc file.

Q. Completion goes awry when I try to complete on something that contains a colon.

A. This is actually a 'feature' of bash. bash recognises a colon as starting a new completion token, which is often what you want when completing something like a PATH variable:

export PATH=/bin:/sbin:/usr<Tab>

Without the special treatment of the colon, the above wouldn't work without programmable completion, so it has long been a feature of the shell.

Unfortunately, you don't want the colon to be treated as a special case when doing something like:

man File::B<Tab>

Here, the colons make bash think that it's completing a new token that begins with 'B'.

Unfortunately, there's no way to turn this off. The only thing you can do is escape the colons with a backslash.

Q. Why is rpm completion so slow with -q?

A. Probably because the database is being queried every time and this uses a lot of memory.

You can make this faster by pregenerating the list of installed packages on the system. Make sure you have a readable file called /var/log/rpmpkgs. It's generated by /etc/cron.daily/rpm on some Red Hat and Mandrake and derivative Linux systems.

If you don't have such a cron job, make one:

#!/bin/sh

rpm -qa --qf '%{name}-%{version}-%{release}.%{arch}.rpm\n' 2>&1 \
        | sort >/var/log/rpmpkgs

rpm completion will use this flat text file instead of the RPM database, unless it detects that the database has changed since the file was created, in which case it will still use the database to ensure accuracy.

Q. bash-completion interferes with my command_not_found_handle function (or the other way around)!

A. If your command_not_found_handle function is not intended to address (possibly missing) commands invoked during bash programmable completion functions, you can account for this in the function by, for example, testing if the $COMP_LINE variable is set and taking appropriate action, typically returning early and silently with success.

Q. Can tab completion be made even easier?

A. The readline(3) library offers a few settings that can make tab completion easier (or at least different) to use.

For example, try putting the following in either /etc/inputrc or ~/.inputrc:

set show-all-if-ambiguous on

This will allow single tab completion as opposed to requiring a double tab. This makes things much more pleasant, in our opinion.

set visible-stats on

This will suffix each returned file completion with a character denoting its type, in a similar way to ls(1) with -F or --classify.

set page-completions off

This turns off the use of the internal pager when returning long completion lists.

Q. Is bash the be-all-and-end-all of completion as far as shells go?

A. Absolutely not. zsh has an extremely sophisticated completion system that offers many features absent from the bash implementation. Its users often cannot resist pointing this out. More information can be found at https://www.zsh.org/.

Q. What is the search order for the completion file of each target command?

A. The completion files of commands are looked up by the shell function __load_completion. Here, the search order in bash-completion >= 2.12 is explained.

1. BASH_COMPLETION_USER_DIR. The subdirectory completions of each paths in BASH_COMPLETION_USER_DIR separated by colons is considered for a completion directory.
2. The location of the main bash_completion file. The subdirectory completions in the same directory as bash_completion is considered.
3. The location of the target command. When the real location of the command is in the directory <prefix>/bin or <prefix>/sbin, the directory <prefix>/share/bash-completion/completions is considered.
4. XDG_DATA_DIRS (or the system directories /usr/local/share:/usr/share if empty). The subdirectory bash-completion/completions of each paths in XDG_DATA_DIRS separated by colons is considered.

The completion files of the name <cmd> or <cmd>.bash, where <cmd> is the name of the target command, are searched in the above completion directories in order. The file that is found first is used. When no completion file is found in any completion directories in this process, the completion files of the name _<cmd> is next searched in the completion directories in order.