Bash script for scaling all images in a directory. Includes cropping for ninepatch images

scale-and-crop.sh

#
# Check that the correct number of arguments have been given.
#
if [ $# -ne 3 ]; then
    echo
    echo [Error] Usage .scale.sh input_dir output_dir scale
    echo
    exit 1
fi

INPUT_DIR=$1
OUTPUT_DIR=$2
SCALE=$3

#
# Check that the input directory exists.
#
if [ ! -d $INPUT_DIR ]; then
    echo
    echo [Error] Cannot find directory $INPUT_DIR
    echo
fi

#
# If the output directory does not exist, then create it.
#
if [ ! -d $OUTPUT_DIR ]; then
    echo
    echo Directory $OUTPUT_DIR not found. Creating empty directory...
    echo
    mkdir $OUTPUT_DIR
fi

#
# Check the third parameter is a positive integer.
#
re='^[0-9]+$'
if ! [[ $SCALE =~ $re ]]; then
   echo [Error] scale should be a positive integer. &2; exit 1
fi

#
# Scale each .png file.
#
for file in $INPUT_DIR/*.png ; do
    NEW_FILENAME="${OUTPUT_DIR}$(basename $file)"
    echo Scaling and cropping $NEW_FILENAME
    OFFSET=$(expr $SCALE - 1)
    convert $file -scale ${SCALE}00% $NEW_FILENAME
    convert $NEW_FILENAME -crop +${OFFSET}+${OFFSET} +repage $NEW_FILENAME
    convert $NEW_FILENAME -crop -${OFFSET}-${OFFSET} +repage $NEW_FILENAME
done