pngopt: A wrapper for pngcrush, that makes it easier to use for overriding images with its optimized output (e.g ./pngopt filea.png fileb.png filec.png). If a file is optimized it outputs the filename with percentage reduction.

pngopt.sh

#!/bin/bash

# pngopt: A wrapper for pngcrush, that makes it easier to use for overriding
#         images with its optimized output.
#
# use: pngopt FILE1 [FILE2] [FILE3] ...
#
# If a file is optimized it outputs the filename with percentage reduction.
#
#
# Example use:
# To replace filea.png and fileb.png with its optimized counterpart:
# $ pngopt filea.png fileb.png
#

while test $# -gt 0; do
    if [ ! -f "$1" ] ; then
        echo "Error: Bad input file: $1" >&2
        shift
        continue
    fi

    tmpfile=$(tempfile --suffix ".png")
    pngcrush "$1" $tmpfile > /dev/null
    filesizes=$(ls -l "$1" $tmpfile | awk '{print $5}' | xargs echo)
    if <<<$filesizes awk '{exit !($1 > $2)}' ; then
        echo -n "$1 "
        <<<$filesizes  awk '{printf "(%.2f", (100 * ($1/$2 - 1)) ; print " %)"}'
        cp $tmpfile "$1"
        rm $tmpfile
    fi
    shift
done