Bash script for batch-scaling images in a directory.

scale.sh

#!/bin/bash

#
# 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"
    convert $file -scale "${SCALE}00%" $NEW_FILENAME
done