I can relate to your pain! I find it amazing that it's usually at least half way through a book that a development editor tells me that I've been using the wrong naming scheme for the chapters or figures all along. The chapters aren't too bad, there are usually only 15-25 in a book total, but figures, well, I can have hundreds of 'em too.

To solve your problem, I noticed that you have a nice, regular pattern that you're using and that creating the new file names is purely dependent on being able to extract the specific information from the old file names.

This is where the Linux (and Mac OS X) cut command is a great tool. To extract just the third and fourth characters, for example: cut -c3-4 works just fine.

The basic logic of this solution then is to, in a loop, extract the chapter and figure numbers from the existing filename, normalize the figure number to three digits, then create a new filename by putting those informational items in a different order. Make sense?

Here's my short little script to do the job:

#!/bin/sh

for name in *TIF
do
  chap="$(echo $name | cut -c3-4)"
  fig="$(echo $name | cut -c5- | cut -d. -f1)"
  if [ $(echo $fig | wc -c) -eq 3 ] ; then
    fig="0$fig"
  fi
  # change the following 'mv' to a 'cp' for insurance
  mv $name "${chap}FIG${fig}.TIF"
done

exit 0

As you can see here, the chapter number is extracted by pulling out the third and fourth characters, and the figure number is extracted by discarding the first four characters of the filename, then grabbing everything up to, but not including, the '.' separator.

The wc invocation is a lazy way to figure out how many characters are in the figure value $fig (including a carriage return added by the echo statement). If it's three, that is, two plus the carriage return, then simple preface an additional zero to normalize them all to three character figure values.

Finally, the new filename is built with ${chap}FIG${fig}.TIF, where the curly braces are required to clearly delimit variables names versus characters to actually include in the filename itself.

Save this script to a text file while in an xterm, or the Mac Terminal application, then, presuming you named it fixnames, run it with: sh fixnames in the directory that contains your existing figures. Within just a second or two all the files should be renamed properly and you should be good to go. Good luck!