A simple CLI parser in Bash

simple-cli-parser.bash

#!/usr/bin/env bash

print_help () { echo "Option -f \${file}: Set file"; exit 0; }
fail () { echo "Error: $*" >&2; exit 1; }
unset file

OPTIND=1
while getopts :f:h-: option
do case $option in
       h ) print_help;;
       f ) file=$OPTARG;;
       - ) case $OPTARG in
               file ) fail "Option \"$OPTARG\" missing argument";;
               file=* ) file=${OPTARG#*=};;
               help ) print_help;;
               help=* ) fail "Option \"${OPTARG%%=*}\" has unexpected argument";;
               * ) fail "Unknown long option \"${OPTARG%%=*}\"";;
            esac;;
        '?' ) fail "Unknown short option \"$OPTARG\"";;
        : ) fail "Short option \"$OPTARG\" missing argument";;
        * ) fail "Bad state in getopts (OPTARG=\"$OPTARG\")";;
   esac
done
shift $((OPTIND-1))

echo "File is ${file-unset}"

for (( i=1; i<=$#; ++i ))
do printf "\$@[%d]=\"%s\"\n" $i "${@:i:1}"
done

To parse stuff like --file foo, it should be possible to do a lookahead and advance OPTIND accordingly.

I think I can write this into a function, but gosh is it painful to type on a phone… anyway, it should take a long arg name, a specification for whether the arg should be there, and return results as its own option/optarg. Something like:

case $option in
(-)
  long_opt='' 
  try_arg file required "${@:$OPTIND}"
  try_arg help forbidden "${@:$OPTIND}"
  case long_opt in
    (file) ;;
    (help) ;;
    ('') fail unknown long;; # should only match the empty case
  esac;;
esac

lookahead() {
  if (($# > 1)); then
    long_arg=$1
    ((OPTIND++))
  else return 1
  fi
}

try_arg() {
  if [[ -n $long_opt ]]; then return; fi
  case $OPTARG in
    ($1=*)
      long_opt=$1 long_arg=${OPTARG#*=}
      [[ $2 != forbidden ]] || puke ;;
    ($1)
      long_opt=$1
      if [[ $2 != forbidden ]]; then lookahead "${@:2}" || [[ $2 == optional ]] || puke ; fi
    (*) return;;
  esac
}

(Of course you would not want all the unnecessary string copies.)

@Honor1234560