POSIX portable shell script with arguments [howto: shell script template]

shell_script_template

#!/bin/dash
#
# Template for shell scripts, with "help", both short and long options,
# and arguments.
# POSIX compliant, and following best practices.
# Distributed under WTFPL.

this_program_filename=

# Debug mode, true or false.
debug=true

# Options.
recursive=false
force=false
config_file=
verbose_level=0

quit_with_usage_help()
{
	cat <<EOF
Usage: $this_program_filename [options] directory
Do something with DIRECTORY.

  -r, --recursive       recursively do stuff in all directories because yup;
                          also note the line break formatting and that
                          there's no period at the end of this sentence
  -f, --force           force execution even if the computer doesn't wanna
  -c, --config FILE     specify a configuration file to load
  --verbose=LEVEL       verbose level 0 to 2 (default 0, don't print anything);
                          also note: this option doesn't have the short form

It's a good idea to write here some more information about the script. Blah
blah blah; use the option --force (-f) only when you are angry.

The default configuration file is in /etc/path/...

To do X, you can use one of these commands:
  $this_program_filename -r .

  $this_program_filename ~

However, if the program is very complex, make a man page for it.

Adapted from: <http://mywiki.wooledge.org/BashFAQ/035>
Interesting links:
  <https://github.com/koalaman/shellcheck>
  <https://stackoverflow.com/a/7948533>
  <https://developer.ibm.com/tutorials/l-bash-parameters/>
EOF
# Good width limit is between 70 and 80 columns: --------------------|---------|
	exit 0
}

quit_with_error_msg()
{
	printf '%s: error: %s\n' "$this_program_filename" "$1" >&2
	printf 'Try "%s --help" for more information.\n' \
		"$this_program_filename" >&2
	exit 1
}

# Get the program name preventing echoing of "./" when running directly.
this_program_filename=$( basename "$0" )

# Parse options.
while :; do
	case $1 in
	# Good practice to have both '-h' and '--help'.
	-h|--help)
		quit_with_usage_help
		;;
	-r|--recursive)
		recursive=true
		;;
	-f|--force)
		force=true
		;;
	-c|--config)
		if [ "$2" ]; then
			config_file=$2
			shift
		else
			quit_with_error_msg \
				'--config option: missing argument.\n'
		fi
		;;
	--verbose=?*)
		# Delete everything up to "=" and assign the remainder.
		verbose_level=${1#*=}
		# Validate.
		if [ -z "${verbose_level##*[!0-9]*}" ]; then
			quit_with_error_msg \
				'--verbose option: expected a positive integer.'
		fi
		if [ "$verbose_level" -lt 0 ] || [ "$verbose_level" -gt 2 ]
		then
			quit_with_error_msg '--verbose option: out of range.'
		fi
		;;
	# Handle the case of an empty argument ('--verbose=').
	--verbose=)
		quit_with_error_msg '--verbose option: missing argument.\n'
		;;
	# Double-dash: end of options.
	--)
		shift
		break
		;;
	-?*)
		err=$( printf 'invalid option "%s"\n' "$1" )
		quit_with_error_msg "$err"
		;;
	# Default case: no (more) options.
	*)
		break
	esac
	shift
done

# Print debug information.
if [ $debug = true ]; then
	printf '## Debug info ##\n'
	printf 'Variables dump (options should change these):\n'
	printf ' > recursive: %s\n' "$recursive"
	printf ' > force: %s\n' "$force"
	printf ' > config_file: %s\n' "$config_file"
	printf ' > verbose_level: %d\n' "$verbose_level"
	if [ "$#" -eq 0 ]; then
		printf 'No other arguments after the options.\n'
	else
		printf '%d argument(s) after the options:\n' $#
		for var in "$@"
			do
				printf ' %s\n' "$var"
			done
	fi
	printf '\n'
fi

# Check the parameters after the options.
if [ "$#" -eq 0 ]; then
	quit_with_error_msg 'missing operand (the directory).'
elif [ "$#" -gt 1 ]; then
	quit_with_error_msg 'too many parameters.'
fi
dir_to_process="$*"
if [ ! -d "$dir_to_process" ]; then
	quit_with_error_msg 'No such file or directory.'
fi

# The rest of the code goes here...
dir_to_process=$( readlink -f "$dir_to_process" )
ls -l "$dir_to_process"
# Etc.

test_the_script

#!/bin/dash

clear

printf "\t\t ## Tests for the script ##"

executable="./shell_script_template"
separator="-------------------------------"
prompt=" > "

command="$executable"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable --help"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable /home"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f -r"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f /home -r"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f /home"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f --config my_configuration.cfg /home"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f --config /home"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f -c my_configuration.cfg -r /home"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f -r --verbose=2 /home"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f -r /home ."
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

command="$executable -f -r ba be bi bo bu"
printf "\n\n\n%s\n\n%s%s\n\n" "$separator" "$prompt" "$command"
$command

# Etc.

printf "\n\n\n\n"