(Git)Bash programmable completion with short '-...' and long '--...' options

Question

I created a completion function inspired by How to Create a Custom Bash Completion Script (which has some obvious errors but I corrected these) and in a newer version on GitHub.

bash_completion_test

#!/bin/bash
#
# bash_completion_test
#
# from https://maskedbyte.com/how-to-create-a-custom-bash-completion-script/
#  and https://github.com/SumuduLansakara/custom-bash-completion-script/blob/master/completer.sh
#

echo 'Begin bash_completion_test...'

# test definitions
_args=(add list remove)
list_args=(student teacher)
list_student_args=(age grade name)
list_student_grade_args=(-a -o --another --option)
list_teacher_args=(name)

#
# Generic hierarchical completion
#
function generic_hierarchical_completion_test() {

    local arguments word_list_ptr word DEBUG
    
    log='bash_completion_test.log'
    echo -n '␃' > $log  # clear log file
    
    DEBUG= #true  # set variable for debugging info in log file
    [[ $DEBUG ]] && echo -n > $log
    
    # Array of individual words in the current command line
    # see https://www.gnu.org/software/bash/manual/bash.html#index-COMP_005fWORDS
    [[ $DEBUG ]] && echo "COMP_WORDS=${COMP_WORDS[@]}" >> $log
    # Second word to last word in the current command line
    arguments=("${COMP_WORDS[@]:1}")
    [[ $DEBUG ]] && echo "arguments=${#arguments[@]}:${arguments[@]}" >> $log

    # Remove last empty word from arguments
    [[ "${#COMP_WORDS[@]}" -gt 1 ]] && unset 'arguments[${#arguments[@]}-1]'
    [[ $DEBUG ]] && echo "arguments=${#arguments[@]}:${arguments[@]}" >> $log

    # Create word list pointer variable from arguments while replacing spaces with '_'
    IFS=_
    word_list_ptr="${arguments[*]}_args[*]"
    unset IFS
    [[ $DEBUG ]] && echo "word_list_ptr=$word_list_ptr" >> $log
    [[ $DEBUG ]] && echo "word_list=${!word_list_ptr}" >> $log
    
    # -W <word list from variable indirected by word_list_ptr>
    # COMP_CWORD: An index into ${COMP_WORDS} of the word containing the current cursor position.
    # see https://www.gnu.org/software/bash/manual/bash.html#index-COMP_005fCWORD
    word=${COMP_WORDS[${COMP_CWORD}]}
    [[ $DEBUG ]] && echo "word=$word" >> $log
    COMPREPLY=( $( compgen -W "${!word_list_ptr}" "$word" ) )
}

complete -F generic_hierarchical_completion_test ct

echo 'End bash_completion_test.'

ct

#!/bin/bash

echo ">> $# arguments: $*"

This works well until $ ct list student grade .

If I $ ct list student grade TAB the result is $ ct list student grade -. So far so good.

If I $ ct list student grade -TABTAB the expected result is:

$ ct list student grade -
--another  --option   -a         -o

But now it's becoming @§$%&!

If I $ ct list student grade --TAB the result is $ ct list student grade -, i.e. the trailing hyphen is removed.

If I $ ct list student grade -aTABTAB it shows all the options correctly but all my aliases in addition (one of them is alias a=alias):

$ ct list student grade -a
--another  --option   -a         -o         ..         a          b          bp         c          df         kc         ll         ls         x

If I $ ct list student grade --aTAB I get an error:

$ ct list student grade --abash: compgen: --: invalid option
compgen: usage: compgen [-abcdefgjksuv] [-o option] [-A action] [-G globpat] [-W wordlist]  [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] [word]

How can I handle short '-...' and long '--...' options correctly?

Answer 1

How can I handle short '-...' and long '--...' options correctly?

You have to separate compgen options and word.

compgen -W "<words>" -- "$word"

Reference

• The Open Group Library, Utility Syntax Guidelines:

Guideline 10:

The first -- argument that is not an option-argument should be accepted as a delimiter indicating the end of options. Any following arguments should be treated as operands, even if they begin with the '-' character.

• Bash Reference Manual, Invoking Bash:

--

A -- signals the end of options and disables further option processing. Any arguments after the -- are treated as filenames and arguments.