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Beyond simple tab completion¶
Matt Taylor wrote on the EADS Linux list:
The wildmenu option in vim shows possible command line completions above the command line, highlighting the currently selected completion option. A follow up email later and Matt says:
Basically, I want bash to show me the completions and Tab to slide through them in the same way vim does it.
The feature is surprisingly easy to achieve with bash, and is
actually a feature of readline making it available to all software that uses
completion functionality from readline.
The option we want is called menu-complete, but it not bound to a key by
default. You can enable menu-complete in all readline-using
applications by editing your ~/.inputrc (or whatever $INPUTRC
points to if it is set) or just for bash if you do not wish to
change the behaviour of other applications.
To change the behaviour by editing the readline configuration file we would do
this:
"\C-a": menu-complete
# Alternative version, enables menu-complete only for bash
$if Bash
"\C-a": menu-complete
$endif
The above tells readline we wish to bind menu-complete to
Control-a, I find that key combination quite comfortable as
Control-a is easy to reach the my keyboard layout and is of little use
in any of the apps I use on a regular basis(I’d feel differently if Home
was inaccessible). You must either re-read the configuration file or restart
the bash session to enable this binding.
To enable the key binding in bash only we could also just edit the appropriate bash startup file:
bind '"\C-a": menu-complete'
You must source the startup file or restart bash to enable this binding, alternatively you can just test the command in your current bash setting until you’re happy with the key combination.
In a follow up email on the list Matt asks if it is possible to make the completion context aware, in much the same the bash-completion package does but without having to write new completion scripts. There are some other quite useful completion modes available in bash, I’ll describe a few below.
M-! tells bash to complete command names; be they actual
on-disk commands, functions or aliases. M-/ completes only filenames,
this can be very useful when bash-completion is refusing to tab complete
a filename for you. C-$ implements variable name completion, this is
most useful when you’re looking to unset or re-set a variable. Variable name
completion isn’t actually necessary if you have bash-completion installed
as it is smart enough to handle this for you in most cases.
And finally, there is a one more incredibly useful completion mode in
bash and that is M-{, it adds all possible completions to the
command line using the brace expansion syntax. For example, if I type ls
~/Git/Local/<M-{> it completes to
/home/jay/Git/Local/{Makefile,countless,dot-configs,haskvim,jrutils}.
Using readline motion commands, especially word motions such as M-f
and M-b to jump forward and backward one word, I can easily apply
a command to a certain set of files in a directory. Just don’t try it on
/usr/bin unless you want to see how bash handles massive command
lines!!
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