scale.sh

#!/bin/bash

echo -n "Source file pattern (e.g. ~/photos/*.jpg): "
read source_pattern

echo -n "Destination path: "
read destination
destination=`eval echo $destination` # Expand to absolute path

echo -n "Desired scale (e.g. 1920x1080): "
read scale

for f in $source_pattern
do
  convert $f -resize $scale'^' -extent $scale $destination/`basename $f`
done