gistfile1.txt

#!/bin/bash
NUM=0
QUEUE=""
MAX_NPROC=2 # default
REPLACE_CMD=0 # no replacement by default
USAGE="A simple wrapper for running processes in parallel.
Usage: `basename $0` [-h] [-r] [-j nb_jobs] command arg_list
 	-h		Shows this help
	-r		Replace asterix * in the command string with argument
	-j nb_jobs 	Set number of simultanious jobs [2]
 Examples:
 	`basename $0` somecommand arg1 arg2 arg3
 	`basename $0` -j 3 \"somecommand -r -p\" arg1 arg2 arg3
 	`basename $0` -j 6 -r \"convert -scale 50% * small/small_*\" *.jpg"

function queue {
	QUEUE="$QUEUE $1"
	NUM=$(($NUM+1))
}

function regeneratequeue {
	OLDREQUEUE=$QUEUE
	QUEUE=""
	NUM=0
	for PID in $OLDREQUEUE
	do
		if [ -d /proc/$PID  ] ; then
			QUEUE="$QUEUE $PID"
			NUM=$(($NUM+1))
		fi
	done
}

function checkqueue {
	OLDCHQUEUE=$QUEUE
	for PID in $OLDCHQUEUE
	do
		if [ ! -d /proc/$PID ] ; then
			regeneratequeue # at least one PID has finished
			break
		fi
	done
}

# parse command line
if [ $# -eq 0 ]; then #  must be at least one arg
	echo "$USAGE" >&2
	exit 1
fi

while getopts j:rh OPT; do # "j:" waits for an argument "h" doesnt
    case $OPT in
	h)	echo "$USAGE"
		exit 0 ;;
	j)	MAX_NPROC=$OPTARG ;;
	r)	REPLACE_CMD=1 ;;
	\?)	# getopts issues an error message
		echo "$USAGE" >&2
		exit 1 ;;
    esac
done

# Main program
echo Using $MAX_NPROC parallel threads
shift `expr $OPTIND - 1` # shift input args, ignore processed args
COMMAND=$1
shift

for INS in $* # for the rest of the arguments
do
	# DEFINE COMMAND
	if [ $REPLACE_CMD -eq 1 ]; then
		CMD=${COMMAND//"*"/$INS}
	else
		CMD="$COMMAND $INS" #append args
	fi
	echo "Running $CMD" 

	$CMD &
	# DEFINE COMMAND END

	PID=$!
	queue $PID

	while [ $NUM -ge $MAX_NPROC ]; do
		checkqueue
		sleep 0.4
	done
done
wait # wait for all processes to finish before exit