#!/bin/sh -x

PROCS=$(grep -c ^processor /proc/cpuinfo)

if [ $# -eq 0 ]; then
    (for f in *.png; do
         echo "$f";
     done) | xargs -P"$PROCS" -d'\n' -n1 optipng -o7
else
    (for f in "$@"; do
         echo "$f";
     done) | xargs -P"$PROCS" -d'\n' -n1 optipng -o7
fi