bash completion for list of possible values of an environment variable

Question

Consider an environment variable that can take a list of arbitrary possible meaningful values. For an example of such an environment variable consider AWS_PROFILE. The list of possible values can be easily computed by some command, e. g. aws configure list-profiles. Is there any way I can write a custom completion such as whenever I type

$ AWS_PROFILE=<TAB>
$ AWS_PROFILE=partial-profile-nam<TAB>

or

$ export AWS_PROFILE=<TAB>
$ export AWS_PROFILE=partial-profile-nam<TAB>

I can get the completion function run and suggest the list of possible values.

Answer 1

Here's a rough example:

# cat compspec
_aws_profiles()
{
    echo {foo,bar}-profile-{1,2}
}

_export_comp()
{
    local cur=$2
    local profiles=$( _aws_profiles )

    if [[ $COMP_LINE == *' AWS_PROFILE='* ]]; then
        COMPREPLY=( $( compgen -W "$profiles" -- "$cur" ) )
        return
    fi
}

complete -F _export_comp -o default -o bashdefault export

$ source ./compspec
$ export AWS_PROFILE=<TAB><TAB>
bar-profile-1  bar-profile-2  foo-profile-1  foo-profile-2
$ export AWS_PROFILE=f
$ export AWS_PROFILE=f<TAB>
$ export AWS_PROFILE=foo-profile-
$ export AWS_PROFILE=foo-profile-<TAB><TAB>
foo-profile-1  foo-profile-2

The above would not work for $ AWS_PROFILE=<TAB>. As a workaround you can define an alias which expands to nothing:

alias %=''
complete -F _export_comp -o default -o bashdefault %

Then you can

$ % AWS_PROFILE=<TAB><TAB>
bar-profile-1  bar-profile-2  foo-profile-1  foo-profile-2