#!/bin/bash

# take two arguments (first a jpeg) and make a thumbnail size version
# stored in the second argument

# but if the second argument is omitted, take the first and add _thumb
# to the base of the filename (assuming it has a dot in it)

if [[ $# -lt  1 || $# -gt 2 ]]
then
  echo "${0}: need 1 or 2 arguments: source-jpeg [destination-file]"
  exit 1
fi

if [ $# == 2 ] 
then  
  (djpeg < $1) | pnmscale -xysize 100 150 | cjpeg > $2
  exit 0
fi
# see Section 3.5.3 of the bash manual for this nonsense
# note we are assuming $1 has at least 1 dot in it
rootname=${1%.*}       # delete last . and what follows
extensionname=${1##*.} # delete last . and what precedes

(djpeg < $1) | pnmscale -xysize 100 150 | cjpeg > "${rootname}"_thumb."${extensionname}"

# exit code is exit code of last command