Bash getopt long options with values usage example.

README.md

Bash getopt long options with values usage example

#!/bin/bash -e

ARGUMENT_LIST=(
  "arg-one"
  "arg-two"
  "arg-three"
)


# read arguments
opts=$(getopt \
  --longoptions "$(printf "%s:," "${ARGUMENT_LIST[@]}")" \
  --name "$(basename "$0")" \
  --options "" \
  -- "$@"
)

eval set --$opts

while [[ $# -gt 0 ]]; do
  case "$1" in
    --arg-one)
      argOne=$2
      shift 2
      ;;

    --arg-two)
      argTwo=$2
      shift 2
      ;;

    --arg-three)
      argThree=$2
      shift 2
      ;;

    *)
      break
      ;;
  esac
done

Note

The eval in eval set --$opts is required as arguments returned by getopt are quoted.

Example

$ ./getopt.sh --arg-one "apple" --arg-two "orange" --arg-three "banana"

Reference

• https://www.bahmanm.com/2015/01/command-line-options-parse-with-getopt.html
• https://dustymabe.com/2013/05/17/easy-getopt-for-a-bash-script/

Even though this works (to some extent, keep reading):

eval set --$opts

it looks really weird and confusing. It works because getopt output starts with a space. But in readers eyes it looks like you call set with some double-dashed option namely --$opts. For the sake of clarity it must be written as

eval set -- $opts

Another story is $opts must be quoted above. I see it in the commits history first you used set --$opts but later you prefixed it with eval. It surely is right, because otherwise any option value containing a space would split into parts. It could be the end of the story, but this is exactly the time when more spaces matter:

> eval set -- $(getopt -o a: -- -a '>    <'); printf 'arg=%s\n' "$@"
arg=-a
arg=> <
arg=--
> eval set -- "$(getopt -o a: -- -a '>    <')"; printf 'arg=%s\n' "$@"
arg=-a
arg=>    <
arg=--
> 

As you see, if unquoted, the value undergoes word-splitting and sequences of chars from $IFS are replaces with a single space in the printed args.

There is one more problem with it being called a 'usage example': it makes a false impression getopt doesnt fail. It should be at least this:

opts=$(getopt \
    --longoptions "$(printf "%s:," "${ARGUMENT_LIST[@]}")" \
    --name "$(basename "$0")" \
    --options "" \
    -- "$@"
) || exit

You might say -e bash option hidden in the shebang would silently kill the script on errors, but it is not a good idea for two reasons:

1. Compatibility-wise the shebang should be /usr/bin/env bash. Because of SC2096 you cant make it both compatible and with -e option to bash.
2. It is hidden out of clear sight and is not explicitly spoken out, bad for learners.