bash-completion

Installation

The easiest way to install this software is to use a package; it is available in many operating system distributions, some examples are listed below. The package's name is usually bash-completion.

Depending on the package, you may still need to source it from either /etc/bashrc or ~/.bashrc (or any other file sourcing those). 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 happen to have only bash >= 4.1 installed, see further if not)

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
make check # optional, requires python3 with pytest >= 3.6 and pexpect, dejagnu, and tcllib
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:

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)
Turn it back on (for example in ~/.bashrc) if you want to use programmable completion for other purposes.

macOS (OS X)

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

Troubleshooting

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 -v or set -x 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 +v or set +x.

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.

Known problems

There seems to be some issue with using the bash built-in cd within Makefiles. When invoked as /bin/sh within Makefiles, bash seems to have a problem changing directory via the cd command. A work-around for this is to define SHELL=/bin/bash within your Makefile. This is believed to be a bug in bash.
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.
If you are seeing 'unbound variable' warnings from bash when hitting <Tab>, this is because you have either set -u or set -o nounset somewhere in your start-up files. This causes bash to flag the use of any uninitialised shell variables as an error.

Whilst we try to avoid references to uninitialised variables in the code, there seem to be at least some cases where bash issues this warning even though the variable in question has been initialised.

One place this appears to occur is within the _muttconffiles() helper function used by mutt completion, where the function calls itself recursively. This seems to confuse bash and it issues spurious warnings if nounset is set.

FAQ

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) 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 on demand. 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. 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 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 other directory (which only present for backwards compatibility) is compatdir (get it with pkg-config --variable=compatdir bash-completion) from which files are loaded 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 = # 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})

Q. I use CVS in combination with passwordless SSH access to my remote repository. How can I have the cvs command complete on remotely checked-out files where relevant?

A. Define $COMP_CVS_REMOTE. Setting this to anything will result in the behaviour you would like.

Q. When I'm running a ./configure script and completion returns a list of long options to me, some of these take a parameter, e.g. --this-option=DESCRIPTION.

Running ./configure --help lists these descriptions, but everything after the = is stripped when returning completions, so I don't know what kind of data is expected as a given option's parameter.

Is there a way of getting ./configure completion to return the entire option string, so that I can see what kind of data is required and then simply delete the descriptive text and add my own data?

A. Define $COMP_CONFIGURE_HINTS. Setting this to anything will result in the behaviour you would like.

Q. When doing tar completion on a file within a tar file like this:

tar tzvf foo.tar.gz <Tab>

the pathnames contained in the tar file are not displayed correctly. The slashes are removed, and everything looks like it's in a single directory. Why is this?

A. It's a choice we had to make. bash's programmable completion is limited in how it handles the list of possible completions it returns.

Because the paths returned from within the tar file are likely not existing paths on the file system, -o dirnames must be passed to the complete built-in to make it treat them as such. However, then bash will append a space when completing on directories during pathname completion to the tar files themselves.

It's more important to have proper completion of paths to tar files than it is to have completion for their contents, so this sacrifice was made and -o filenames is used with complete instead.

If you would rather have correct path completion for tar file contents, define $COMP_TAR_INTERNAL_PATHS before sourcing bash_completion.

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_handler function!

A. If your command_not_found_handler function is not intended to address (possibly missing) commands invoked during bash programmable completion functions, you can account for this by, for example, testing if the $COMP_* variables are set and taking appropriate bypass or other action.

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: http://www.zsh.org/

License

oilshell/bash-completion

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