Compress PNG file with Pngcrush

pngcrusher.sh

#!/bin/bash
# Name of File: pngcrusher.sh
# Author:       Vayn a.k.a. VT <vayn@vayn.de>
# Name:         PNG Crusher
# Thanks To:    Jyo <http://jyorr.com> 
# License:
#    Released under the MIT, BSD, and GPL Licenses.
#    This is free software: you are free to change and redistribute it.
#    There is NO WARRANTY, to the extent permitted by law.

E_BADDIR=65

usage() {
    echo "PNG Crusher extends function of Pngcrush to compress all png files in a directory. 
Usage: `basename $0` [option]... [dir]...
    -h help"
}

crush() {
    dir=$(readlink -f "$1")
    if [[ ! -d "$dir" ]]; then
        echo "Cannot open \"$dir\" as directory."
        exit $E_BADDIR
    else
        counter=0
        for filename in "$dir"/*; do
            if [[ -f "$filename" && $(file "$filename" | awk '{print $2}') = PNG ]]; then
                echo "Processing $filename"
                pngcrush "$filename" "$filename.tmp"
                mv "$filename.tmp" "filename"
                ((counter++))
            fi
        done

        if [[ $counter -gt 0 ]]; then
            echo "$counter png file(s) processed."
            exit 0
        else
            echo "No png file found."
            exit 1
        fi

    fi
}

if [[ $# -eq 0 || "$1" = "-h" ]]; then
    usage;
    exit 0;
else
    crush "$1"
fi