Bash Completion

Bash completion rocks. Ubuntu does a great job of populating /etc/bash_completion.d/ with tons of glue to bash complete lots of commands.

Here is how you can write your own for your own programs!:

Example

wa() { cd /some/dir/webapp/$1 ; }
_webapp() {
    local cur
    cur=${COMP_WORDS[COMP_CWORD]}
    COMPREPLY=( $( compgen -S/ -d /some/dir/webapp/$cur | cut -b 18- ) )
}
complete -o nospace -F _webapp wa

Explaination

You need:

* A bash function that will define a COMPREPLY variable. Usually called _$PROGRAMNAME
* Logic inside that function to figure out what to return for possible completions (using the compgen command, usually)
* Use the "complete" command to register your tab completions ( complete -F _mycommand mycommand )
* Put this in a file in /etc/bash_completion.d/
* source /etc/bash_completion or re-login to take effect.

Compgen Details

compgen: compgen [-abcdefgjksuv] [-o option]  [-A action] [-G globpat] [-W wordlist]  [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] [word]
    Display possible completions depending on the options.
    
    Intended to be used from within a shell function generating possible
    completions.  If the optional WORD argument is supplied, matches against
    WORD are generated.
    
    Exit Status:
    Returns success unless an invalid option is supplied or an error occurs.

Not super helpful. Here is more more info at the manual:

• https://www.gnu.org/software/bash/manual/bash.html#Programmable-Completion-Builtins

References

• http://sixohthree.com/867/bash-completion