convert png to jpg while retaining the original mod date

png2jpg.sh

#!/bin/bash
#-----------------------------------------------------------
# Copyright (C) 2015 GRUBERND http://grubernd.at
# released under a FreeBSD License
#
# convert png to jpg while retaining the original mod date
# dependicies: imagemagick
#-----------------------------------------------------------

shopt -s nullglob nocaseglob

for d in *; do
    if [ -d "$d" ]; then
        pushd "$d"
        echo $d
        for f in *.png; do
            mogrify -format jpg -- "$f"
            j=${f%.*}.jpg
            touch -m --date="$(stat -c %y $f)" "$j"
            rm "$f"
        done
        popd
    fi
done

#-----------------------------------------------------------
# same as a oneliner for insta-use:

# shopt -s nullglob nocaseglob; for d in *; do if [ -d "$d" ]; then pushd "$d"; echo $d; for f in *.png; do mogrify -format jpg -- "$f"; j=${f%.*}.jpg; touch -m --date="$(stat -c %y $f)" "$j"; rm "$f"; done; popd; fi; done