#!/bin/sh
set -eu


usage() {
	cat <<-'EOF'
		Usage:
		  shesc [CONTENT...]
		  shesc -h
	EOF
}

help() {
	cat <<-'EOF'


		Options:
		  -h, --help    show this message

		  CONTENT       a literal string to be escaped


		Convert data to/from POSIX sh double quote string escaping.  If
		CONTENT is not given, get data from STDIN.


		Examples:

		  Escape sh control characters in a string:

		    $ printf 'content="%s"\n' "$(shesc '"string" $(dollar "`cmd`") \ ')"
		    content="\"string\" \$(dollar \"\`cmd\`\") \\ "


		  Escape the content from a file:

		    $ shesc < file.conf
	EOF
}


for flag in "$@"; do
	case "$flag" in
		(--)
			break
			;;
		(--help)
			usage
			help
			exit
			;;
		(*)
			;;
	esac
done

while getopts 'h' flag; do
	case "$flag" in
		(h)
			usage
			help
			exit
			;;
		(*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))



esc() {
	sed 's|\([\\`"$]\)|\\\1|g'
}


if [ $# = 0 ]; then
	esc
else
	for s in "$@"; do
		printf '%s\n' "$s" | esc
	done
fi