#!/bin/sh
[ $# -eq 0 ] && { echo "usage: rejpg file" >&2; exit 1; }
tmpfile=$(mktemp ~/.rejpg.XXXXXX) || exit 1
djpeg "$1" | cjpeg -quality 90 >$tmpfile
mv -f $tmpfile "$1" && chmod go+r "$1"
rm -f $tmpfile
.