parallel -j 3 prog *.jpg
Here 3 prog program will run simultanously
or
parallel -j 3 "prog -r -A=40" *.jpg
to pass args to prog.
Furthermore, -r allows even more sophisticated commands by replacing asterisks in the command string by the argument:
parallel -j 6 -r "convert -scale 50% * small/small_*" *.jpg
I.e. this executes convert -scale 50% file1.jpg small/small_file1.jpg for all the jpg files. This is a real-life example for scaling down images by 50% (requires imagemagick).
Finally, here’s the script. It can be easily manipulated to handle different jobs, too. Just write your command between #DEFINE COMMAND and #DEFINE COMMAND END.
Here is the parallel program
#!/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"
$CMD &
#Change:
#$CMD &
#To:
#eval “$CMD &”
#If you want to do things like:
#par.sh ‘tr -d ” ” * > $(basename * .txt)-stripped.txt’ *.txt
#Without the eval it’ll treat > and $(basename…) as arguments to tr.
# DEFINE COMMAND END
PID=$!
queue $PID
while [ $NUM -ge $MAX_NPROC ]; do
checkqueue
sleep 0.4
done
done
wait # wait for all processes to finish before exit
Source is at http://pebblesinthesand.wordpress.com/2008/05/22/a-srcipt-for-running-processes-in-parallel-in-bash/
