#!/bin/sh
set -eu

usage() {
	cat <<-'EOF'
		Usage:
		  without-env ENVVAR PATH -- COMMAND...
		  without-env [-h]
	EOF
}

help() {
	cat <<-'EOF'

		Options:
		  -h, --help    show this message

		Examples:

		  Execute "command -V" filtering ~/bin, to get where "w3m" is
		  in $PATH, other than ~/bin:
		    $ without-env PATH ~/bin -- command -v w3m

		  Compile foo.c, excluding ~/.local/include
		  from $C_INCLUDE_PATH:
		    $ without-env C_INCLUDE_PATH ~/.local/include -- cc -co foo.o foo.c
	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))

assert_arg() {
	if [ -z "$1" ]; then
		printf 'Missing %s\n' "$2" >&2
		exit 2
	fi
}

assert_arg "${1:-}" 'ENVVAR'
assert_arg "${2:-}" 'PATH'
assert_arg "${3:-}" '--'

eval "export $1=\"\$(echo \"\$$1\" | sed \"s|\$2:||g\")\""
shift # drop $1
shift # drop $2
shift # drop --

"$@"