#!/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

sourcefile=$1
if [ $# == 2 ] 
then
    destfile=$2
else
# 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=${1##*.} # delete last . and what precedes
    destfile="${rootname}"_thumb."${extensionname}"
fi

(djpeg < $sourcefile) | pnmscale -xysize 100 150 | cjpeg > $destfile

# exit code is exit code of last command