#!/bin/sh

help() {
	echo "loop - execute command in loop

USAGE:
	loop [OPTION]... <COMMAND>

OPTIONS:
	-n INTERVAL   sleep for given INTERVAL time between loops
	                all arguments of \`sleep\` command are valid
	-c COUNT      maximum count of loops (default: 1000)
	-s            clear screen for every execution
	-q            quiet, redirect output to /dev/null
	-h            show this help message

ENVIRONMENT VARIABLES:
	LOOP_INTERVAL   set INTERVAL time
	MAX_LOOP_COUNT	set loop COUNT"
}

err() { printf 'loop: %s\n' "$@" >&2; exit 1; }

while getopts 'sc:n:qh' o; do case "$o" in
	s) cflag=1 ;;
	n) export LOOP_INTERVAL="$OPTARG" ;;
	c) export MAX_LOOP_COUNT="$OPTARG" ;;
	q) qflag=1 ;;
	h) help; exit ;;
	*) err "invalid option -- $OPTARG" ;;
esac done
shift $((OPTIND - 1))

[ "$#" -lt 1 ] && err "no COMMAND given"
cmds="$*"
max_count="${MAX_LOOP_COUNT:-1000}"
[ -n "$LOOP_INTERVAL" ] && cmds="$cmds; sleep '$LOOP_INTERVAL'"
[ "$cflag" = 1 ] && cmds="clear; $cmds"
[ "$qflag" = 1 ] && cmds="$cmds >/dev/null"

for count in $(seq "$max_count"); do
	eval "$cmds" || break
done

[ "$count" -ge "$max_count" ] && err "reached max loop COUNT: $max_count"