Do not shift after parsing args if the only defined arg is help

[yeldiRium]

After using argbash for quite a few arguments-heavy scripts and liking it a lot, I started to add it to most of my scripts to have a consistent help text and to be able to declare used environment variables.
During that I encountered the very minor issue, that argbash produces code that contains a shellcheck error when no arguments are defined.

A minimal example looks like this:

#!/usr/bin/env bash

# ARG_HELP([Does a thing])
# ARG_USE_ENV([SOME_ENV],[],[Contains important config])
# ARGBASH_GO()
# [ <-- needed because of Argbash

echo "${SOME_ENV}"

# ] <-- needed because of Argbash

This produces the following argument parsing code:

parse_commandline()
{
	while test $# -gt 0
	do
		_key="$1"
		case "$_key" in
			-h|--help)
				print_help
				exit 0
				;;
			-h*)
				print_help
				exit 0
				;;
			*)
				_PRINT_HELP=yes die "FATAL ERROR: Got an unexpected argument '$1'" 1
				;;
		esac
		shift
	done
}

Shellcheck complains about the shift in line 19, since it is unreachable.
I would expect argbash to realize this and omit the shift.

As I said I think this is a very minor issue.
If I get around to reading more m4, I might open another PR.

[matejak]

I have added a waiver to the shellcheck for this reason, because I came to a conclusion that it is not worth it, at least my time :-)
The problem is that not only the shift, but the entire loop is redundant if the script doesn't accept any other arguments than action arguments.
To address this, there would have to exist a global variable that would be set to a truthy value if the script accepts an argument that justifies the existence of a loop, and then the argument loop would be generated if so, or omitted entirely if not.

That's a lot of ifs to get rid of a warning that only extremely simple scripts raise.
I see that you can use other Argbash features s.a. env variables, which are useful but which don't require a loop, so this raises the priority a bit, but it's still quite low.

I will leave this issue open for some time to see whether there is a discussion, or I can help you if you decide to go for a PR :-)