How to use bash command completion so that only files within a particular directory are completed?

Question

Suppose I have a bash function specialcat that cats a file in the ~/Special directory

specialcat () {
    cat ~/Special/$1
}

Suppose the ~/Special directory was set up like so:

mkdir ~/Special
echo This is the first special file > ~/Special/firstfile
echo This is the second special file > ~/Special/secondfile

The specialcat function is used like:

> specialcat firstfile
This is the first special file

I want to enable argument completion so that

> specialcat firstf[TAB]

produces

> specialcat firstfile

regardless of what the current working directory is and what files happen to be there.

This is my attempt so far

_options_specialcat () {
    COMPREPLY=( $(compgen -W "$(ls ~/Special)") )
}

complete -F _options_specialcat specialcat

which leads to

> specialcat firstf[TAB]
firstfile   secondfile  
> specialcat firstf

That is, pressing tab on a partial file name will display the list of files, but will not complete the command.

How do I alter my _options_specialcat function to produce the desired behavior?

Answer 1

You need to filter the list by the current argument, so:

COMPREPLY=( $(compgen -W "$(ls ~/Special)" -- "$2") )