Hi Chris
I am a bit of a n00b in regards to shell scripts.
I have bought this book: http://www.takecontrolbooks.com/command-line?pt=TB1270
Which I hope helps with this.
But in this regard, then my shell script should look like this.
export PATH=/usr/local/bin:$PATH;
convert /tmp/compare/Diff_$KMVAR_CompareRunTimes.jpg /tmp/compare/$KMVAR_ComparePDFname
And I can confirm that it works perfectly.