Create thumbnails from images in current directory.

thumbnails.sh

#!/bin/bash

images=$(ls | grep -e '.[jpg|png]$')

for image in $images
do
  base=$(basename "$image")
  name="${base%.*}"
  echo "Thumbnailing $image..."
  convert "$image" -thumbnail 140x140^ -gravity center -extent 140x140 "${name}_thumb.jpg"
done