Run «command» only every «number» time invoked

every

#!/usr/bin/env bash

progname=$(basename $0)
version="1.0 (2014-08-17)"
step=2

function create_hash {
	openssl dgst -sha1 -binary <<< "$1" | xxd -p
}

while getopts ':n:vh' opt; do
	case $opt in
		n)  step=$OPTARG ;;
		v)  echo "$progname $version"; exit ;;
		:)  echo >&2 "$progname: option requires an argument -- $OPTARG"; exit 1 ;;
		\?) echo >&2 "$progname: illegal option: -- $OPTARG"; exit 1 ;;

		h)
			echo "$progname $version"
			echo "Usage: $progname [-n number] command [argument ...]"
			echo "       $progname [-v|-h]"
			echo "Options:"
			echo " -n <number>   Run every <number> time. Defaults to 2."
			echo " -v            Print version information."
			echo " -h            Show this information."
			exit
		;;
	esac
done

if [ $OPTIND -gt $# ]; then
	echo >&2 "$progname: no command specified. Use -h for usage options."
	exit 1
fi

file="${XDG_DATA_HOME:-$HOME/.local/share}/${progname}/$(create_hash "$*")"

if [ ! -f "$file" ]; then
	mkdir -p "$(dirname "$file")"
	echo >"$file" 1
fi

value=$(head -n1 "$file")

if [ $value -ge $step ]; then
	rm "$file"
	exec "${@:$OPTIND}"
fi

printf "%d\n# Last run: %s\n# Command: %s\n" "$(( $value + 1 ))" "$(date)" "${*:$OPTIND}" >"$file"