squeue

#!/bin/sh
#
# Bourne Shell implementation of a simple queue command.
# This script comes in handy for hot-keys and the like.
#
# It does not support a timer or other means of job triggers
# (e.g. system load).
#
# License: MIT
# Copyright: Tobias Farrenkopf tf@emptyset.de

set -o nounset

NQUEUE="/tmp/${USER}_simple_queue"

usage() {
	echo "Usage: $(basename "$0") [COMMAND]"
	echo 'Appends every COMMAND to a queue and executes them one by one.'
	echo 'It reads COMMAND from standard input or from ARGS.'
	echo
	echo '-h, --help    display this help and exit'
	echo '-q, --quit    terminate the queue process'
	echo '-d            allow duplicate COMMAND in the queue'
}

echoerr() { echo "$@" 1>&2; }

check_running() {
	if [ -p "$NQUEUE" ] && $(ps x | grep -q "$0"); then
		echo 1
	else
		echo 0
	fi
}

run_loop() {
	last_job=
	# read from the named pipe. The first char (duplicate flag)
	# is removed from the job and evaluated.
	while read job <"$NQUEUE"
	do
		skip_duplicate=${job%${job#?}}
		job=${job#?}
		if [ "$skip_duplicate" -eq 1 ] && [ "$job" = "$last_job" ]; then
			echoerr "WARN: skipping duplicate job"
		elif [ -n "$job" ]; then
			last_job="$job"
			eval "$job"
		fi
		sleep .2
	done
}

# Main
#
skip_duplicate=1

# fork the run_loop if not running
if [ $(check_running) -eq 0 ]; then
	rm -f "$NQUEUE"
	mkfifo "$NQUEUE" || exit 1
	run_loop &
fi

if [ ! -p "$NQUEUE" ]; then
	echoerr "ERROR: ${NQUEUE} is not a named pipe. Abort!"
	exit 1
fi

# check for options
if [ $# -ne 0 ]; then
	if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
		usage
		exit 0
	elif [ "$1" = '-q' ] || [ "$1" = "--quit" ]; then
		echo 'Done processing jobs'
		rm -f "$NQUEUE"
		exit 0
	elif [ "$1" = "-d" ]; then
		skip_duplicate=0
		shift
	elif [ ${1%${1#?}} = "-" ]; then
		echoerr "Invalid option ${1}"
		echoerr "Try '$(basename ${0}) --help' for more information."
		exit 1
	fi
fi

if [ $# -ne 0 ]; then
	echo "${skip_duplicate}${@}" > "$NQUEUE"
else
	while read LINE; do
		echo "${skip_duplicate}${LINE}" > "$NQUEUE"
	done
fi