Bash script for recursive optimization png files

compress-png.sh

#!/bin/bash
if [ -z "$1" ]
    then echo "
Usage: script [directory] [change files]

Arguments:
directory - script take all jpg files from directory
change files - if true files will be changed, otherwise (default) then will not change any files (test run)

Requirements: optipng
"
else
    dirName=$1
    changeFiles=$2
    startDirSize=$(du -s $dirName | cut -f 1)

    find $dirName -type f -iname \*.png | while read file; do
        echo "----------"
        fileEscaped=$(echo $file | sed 's/ /\\ /g')
        fileEscaped=$(echo $fileEscaped | sed 's/[(]/\\(/g;s/[)]/\\)/g')

        if [[ $changeFiles == true ]]; then
            simulationMode=""
        else
            simulationMode="-simulate "
        fi

        command="optipng -o1 -q $simulationMode \"$file\""
        echo $command
        eval $command
    done;
    echo "=========="
    endSize=$(du -s $dirName | cut -f 1)
    diffSize=$(($startDirSize - $endSize))
    diffPercent=$(($(($diffSize*100))/$startDirSize));
    echo "Saved $diffSize KB ($diffPercent%)"
fi