#!/bin/bash
if [ -z "$1" ] || [ -z "$2" ]
    then echo "
Usage: script [dir name] [quality] <options>
Arguments:
directory name - script take all jpg files from dir
quality threshold - jpg quality value (0-100); if file has higher quality will be processed lossy, otherwise lossless
additional options (optional)

Default options are: p,s
p - preserve file timestamp
s - strip all markers (xmp, iptc etc.)

Example:
./compress-jpg.sh img-test/ 93 -n

Due to bash oddities, better have dirs and files without white spaces or parentheses. I tried to handle this but... this is
bash.
"
else
    # Progressive option is inefficient for small images; that is "normal" will make smaller files
    PROGRESSIVE_THRESHOLD=10240
    dirName=$1
    qualityThreshold=$2
    additionalOptions=$3
    startDirSize=$(du -s $dirName | cut -f 1)
    touch error.log
    rm error.log

    find $dirName -type f -print0 | while read -d $'\0' file; do
        # Escaping white spaces
        file=$(echo $file | sed 's/ /\\ /g')
        # Escaping parentheses
        file=$(echo $file | sed 's/[(]/\\(/g;s/[)]/\\)/g')

        qualityValue=$(($(identify -verbose "$file" | grep 'Quality:' | sed 's/[^0-9]//g')))
        fileSize=$(stat --printf="%s" "$file")

        optionProgressive=" "
        if (($fileSize > $PROGRESSIVE_THRESHOLD)); then
            optionProgressive="--all-progressive"
        else
            optionProgressive="--all-normal"
        fi

        optionQuality=" "
        if (($qualityValue > $qualityThreshold)); then
            optionQuality="--max=$qualityThreshold"
        fi

        command="jpegoptim -p -s $optionQuality $optionProgressive $additionalOptions $file"
        echo $command
        eval $command 2>> error.log
        echo "----------"
    done;
    echo "=========="
    endSize=$(du -s $dirName | cut -f 1)
    diffSize=$(($startDirSize - $endSize))
    diffPercent=$(($(($diffSize*100))/$startDirSize));
    echo "Saved $diffSize KB ($diffPercent%)"
    touch error.log
    printf "Errors:\n" && cat error.log
fi