Optimize Images sh script. Original: http://hugogiraudel.com/2013/07/29/optimizing-with-bash/

optimize.sh

#!/bin/bash

# Note, apt-get on Ubuntu seems to be providing an out of date optipng.
# Try doing this to install version 0.7.6
# Run optipng -v to see the version you have installed.

# wget http://downloads.sourceforge.net/project/optipng/OptiPNG/optipng-0.7.6/optipng-0.7.6.tar.gz
# tar xvf optipng-0.7.6.tar.gz
# cd optipng-0.7.6
# ./configure
# make
# sudo cp /src/optipng/optipng /usr/local/bin/optipng
# optipng -v

PROGNAME=${0##*/}
INPUT=''
QUIET='0'
NOSTATS='0'
RETAINPATH='0'
max_input_size=0
max_output_size=0

usage()
{
  cat <<EO
Usage: $PROGNAME [options]
Script to optimize JPG and PNG images in a directory.
Options:
EO
cat <<EO | column -s\& -t
	-h, --help  	   & shows this help
	-q, --quiet 	   & disables output
	-i, --input [dir]  & specify input directory (current directory by default)
	-o, --output [dir] & specify output directory ("output" by default)
	-ns, --no-stats    & no stats at the end
	-r, --retain-path  & retains the directory structure when writing into output
EO
}

command_exists () {
    type "$1" &> /dev/null ;
}

# $1: input image
# $2: output image 
optimize_image()
{
	input_file_size=$(stat -c%s "$1")
	max_input_size=$(expr $max_input_size + $input_file_size)

	if [ "${1##*.}" = "png" ]; then
		optipng -o2 -clobber -strip all -quiet $1 -out $2
		# pngcrush -q -rem alla -reduce -m 7 $2 $2 >/dev/null
		#pngcrush -rem alla -nofilecheck -reduce -m 7 $2 $2>/dev/null
		#pngcrush -rem alla -nofilecheck -reduce -m 7 -ow $2 > /dev/null
		#pngcrush -reduce -brute -ow $2 > /dev/null
	fi
	if [ "${1##*.}" = "jpg" -o "${1##*.}" = "jpeg" ]; then
		jpegtran -copy none -optimize -progressive $1 > $2
	fi

	output_file_size=$(stat -c%s "$2")
	max_output_size=$(expr $max_output_size + $output_file_size)
}

get_max_file_length()
{
	local maxlength=0

	IMAGES=$(find $INPUT -regextype posix-extended -regex '.*\.(jpg|jpeg|png)' | grep -v $OUTPUT)

	for CURRENT_IMAGE in $IMAGES; do
		filename=$(basename "$CURRENT_IMAGE")
		if [[ ${#filename} -gt $maxlength ]]; then
			maxlength=${#filename}
		fi
	done

	echo "$maxlength"	
}

main()
{
	# If $INPUT is empty, then we use current directory
	if [[ "$INPUT" == "" ]]; then
		INPUT=$(pwd)
	fi

	# If $OUTPUT is empty, then we use the directory "output" in the current directory
	if [[ "$OUTPUT" == "" ]]; then
		OUTPUT=$(pwd)/output
	fi

	# We create the output directory
	mkdir -p $OUTPUT

	# To avoid some troubles with filename with spaces, we store the current IFS (Internal File Separator)...
	SAVEIFS=$IFS
	# ...and we set a new one
	IFS=$(echo -en "\n\b")

	max_filelength=`get_max_file_length`
	pad=$(printf '%0.1s' "."{1..600})
	sDone=' [ DONE ]'
	linelength=$(expr $max_filelength + ${#sDone} + 5)

	# Search of all jpg/jpeg/png in $INPUT
	# We remove images from $OUTPUT if $OUTPUT is a subdirectory of $INPUT
	IMAGES=$(find $INPUT -regextype posix-extended -regex '.*\.(jpg|jpeg|png)' | grep -v $OUTPUT)

	if [ "$QUIET" == "0" ]; then
		echo --- Optimizing $INPUT ---
		echo
	fi
	for CURRENT_IMAGE in $IMAGES; do
		filename=$(basename $CURRENT_IMAGE)
		if [ "$QUIET" == "0" ]; then
		    printf '%s ' "$filename"
		    printf '%*.*s' 0 $((linelength - ${#filename} - ${#sDone} )) "$pad"
		fi

		INPUTABS=$(readlink -f $INPUT)

		# If we want to retain the directory path.
		if [ "$RETAINPATH" == "1" ]; then
			# Create a replica of the absolute path in the output directory.
			abspath=$(readlink -f $CURRENT_IMAGE)
			absdirname=$(dirname $abspath)
			trimmeddir=${absdirname#$INPUTABS}
			mkdir -p $OUTPUT$trimmeddir

			
			# Optimize the image.
			optimize_image $CURRENT_IMAGE $OUTPUT/$trimmeddir/$filename	
		else
			# Optimize the image.
			optimize_image $CURRENT_IMAGE $OUTPUT/$filename	
		fi

		if [ "$QUIET" == "0" ]; then
		    printf '%s\n' "$sDone"
		fi
	done

	# we restore the saved IFS
	IFS=$SAVEIFS

	if [ "$NOSTATS" == "0" -a "$QUIET" == "0" ]; then
		echo
		echo "Input: " $(human_readable_filesize $max_input_size)
		echo "Output: " $(human_readable_filesize $max_output_size)
		space_saved=$(expr $max_input_size - $max_output_size)
		echo "Space save: " $(human_readable_filesize $space_saved)
	fi
}

human_readable_filesize()
{
echo -n $1 | awk 'function human(x) {
     s=" b  Kb Mb Gb Tb"
     while (x>=1024 && length(s)>1) 
           {x/=1024; s=substr(s,4)}
     s=substr(s,1,4)
     xf=(s==" b ")?"%5d   ":"%.2f"
     return sprintf( xf"%s", x, s)
  }
  {gsub(/^[0-9]+/, human($1)); print}'
}

SHORTOPTS="h,i:,o:,q,s,r"
LONGOPTS="help,input:,output:,quiet,no-stats,retain-path"
ARGS=$(getopt -s bash --options $SHORTOPTS --longoptions $LONGOPTS --name $PROGNAME -- "$@")

eval set -- "$ARGS"
while true; do
	case $1 in
		-h|--help)
			usage
			exit 0
			;;
		-i|--input)
			shift
			INPUT=$1
			;;
		-o|--output)
			shift
			OUTPUT=$1
			;;
		-q|--quiet)
			QUIET='1'
			;;
		-s|--no-stats)
			NOSTATS='1'
			;;
		-r|--retain-path)
			RETAINPATH='1'
			;;
		--)
			shift
			break
			;;
		*)
			shift
			break
			;;
	esac
	shift
done

if ! command_exists optipng ; then
    echo "Please install optipng.";
    exit;
fi
# if ! command_exists pngcrush ; then
#     echo "Please install pngcrush.";
#     exit;
# fi
if ! command_exists jpegtran ; then
    echo "Please install jpegtran.";
    exit;
fi

main

Changes:
Checks if programs are installed.
clobber is not an option for optipng on ubuntu anymore? Removed.
Can retain directory structure when writing files into output with the -r argument.