A script to optimize (pngcrush) all the images in a folder, and tell you how much space you've saved.

pngcrushall.sh

#!/bin/bash
TOTALIN=0
TOTALSAVED=0
TOTALFILES=0
for png in *.png;
do
	echo "Crushing $png"
	echo "PNG file $png:" >> /tmp/pngcrush.log
	OLDSIZE=$(stat --printf="%s" "$png")
	echo "  Old size: $OLDSIZE" >> /tmp/pngcrush.log
	pngcrush -q -brute "$png" temp.png
	mv -f temp.png "$png"
	NEWSIZE=$(stat --printf="%s" "$png")
	PERCENT=$(echo "scale=4; (($OLDSIZE - $NEWSIZE) / $OLDSIZE) * 100" | bc)
	PERCENT=$(echo "scale=2; $PERCENT / 1" | bc)
	echo "  New size: $NEWSIZE" >> /tmp/pngcrush.log
	echo "  Savings:  $PERCENT%" >> /tmp/pngcrush.log
	let "TOTALIN = $TOTALIN + $OLDSIZE"
	TOTALSAVED=$(echo "$TOTALSAVED + ($OLDSIZE - $NEWSIZE)" | bc)
	let TOTALFILES++
done;

let "TOTALOUT = $TOTALIN - $TOTALSAVED"
TOTALPERCENT=$(echo "scale=4; (($TOTALIN - $TOTALOUT) / $TOTALIN) * 100" | bc)
TOTALPERCENT=$(echo "scale=2; $TOTALPERCENT / 1" | bc)
echo
echo
echo "Crush Report:"
cat /tmp/pngcrush.log
echo ""
echo "========================"
echo "Total PNG count:   $TOTALFILES"
echo "Total bytes in:    $TOTALIN"
echo "Total bytes out:   $TOTALOUT"
echo "Total bytes saved: $TOTALSAVED"
echo "Total percentage:  $TOTALPERCENT%"
rm /tmp/pngcrush.log

Needs pngcrush and bc installed.

Haven't tested on Mac. r/linuxmasterrace