Boilerplate for new POSIX shell scripts

newscript.sh

#!/bin/sh

prog_name=${0##*/}
version=1.0
version_text="Boilerplate for new scripts v$version"
options="h o: q v V"
help_text="Usage: $prog_name [-o <text>] [-hqvV] [<file>]...

Boilerplate for new scripts

        -o <text>  Set an option with a parameter
        -h         Display this help text and exit
        -q         Quiet
        -v         Verbose mode
        -V         Display version information and exit"

main() {
	set_defaults
	parse_options "$@"
	shift $((OPTIND-1))
	# If we want to use `getopts` again, this has to be set to 1.
	OPTIND=1

	# shellcheck disable=2154
	{
		$option_h && usage
		$option_V && version
		$option_q && info() { :; }
		$option_o && info "option 'o' has parameter '$param_o'"
		$option_v && info "verbose mode is on"
	}

	_i=1
	for _file do
		info "operand $_i is '$_file'"
		_i=$((_i+1))
	done
	unset _i _file

	[ -t 0 ] ||
		info "stdin is not a terminal"
}

##########################################################################

# shellcheck disable=2034,2046
set_defaults() {
	set -e
	trap 'clean_exit' EXIT TERM
	trap 'clean_exit HUP' HUP
	trap 'clean_exit INT' INT
	IFS=' '
	set -- $(printf '\n \r \t \033')
	nl=$1 cr=$2 tab=$3 esc=$4
	IFS=\ $tab
}

# For a given optstring, this function sets the variables
# "option_<optchar>" to true/false and param_<optchar> to its parameter.
parse_options() {
	for _opt in $options; do
		# The POSIX spec does not say anything about spaces in the
		# optstring, so lets get rid of them.
		_optstring=$_optstring$_opt
		eval "option_${_opt%:}=false"
	done

	while getopts ":$_optstring" _opt; do
		case $_opt in
			:) usage "option '$OPTARG' requires a parameter" ;;
			\?) usage "unrecognized option '$OPTARG'" ;;
			*)
				eval "option_$_opt=true"
				[ -n "$OPTARG" ] &&
					eval "param_$_opt=\$OPTARG"
			;;
		esac
	done
	unset _opt _optstring OPTARG
}

info()    { printf %s\\n "$*" >&2; }
version() { printf %s\\n "$version_text"; exit; }

error() { 
	_error=${1:-1}
	shift
	printf '%s: Error: %s\n' "$prog_name" "$*" >&2
	exit "$_error"
}

usage() {
	[ $# -ne 0 ] && {
		exec >&2
		printf '%s: %s\n\n' "$prog_name" "$*"
	}
	printf %s\\n "$help_text"
	exit ${1:+1}
}

clean_exit() {
	_exit_status=$?
	trap - EXIT
	info "exiting"

	[ $# -ne 0 ] && {
		trap - "$1"
		kill -s "$1" -$$
	}
	exit "$_exit_status"
}

main "$@"