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 "$@"

Love this as a starting point... Thanks much!
Q: is your overall intent to use the set_defaults() to set the main variables' defaults as well? Currently it sets characters as variables and trap defaults... I ask primarily as I've been adding my own variable defaults near the top of my scripts for easier visibility and proximity to the help_text.

@cometsong I can't reply directly here.

I think in your case I'd add the variables to the top of main().

is it possible to get parse-opts for longer names options?

@epsilon-0 not easily. The beauty of parse_options() is that for it's usage you only have to set the scripts options via the options variable and the rest is done for you. Long options will make it more complex in both, usage and code complexity. I'm not a fan of long options in general to say the least, but I will think about a good way (if there is one).

got it :)

thanks a lot, I think I am fine without the long options, managed to work around it :)