I just reread this and it's funny how much it sounds like homework!
Anyway, my problem was that I didn't know how to make a loop run along a sequence of numbers, rather than iterating over files in a directory. I did this and it worked:
# BUILD THE CLASSPATH WITH A REFERENCE TO EVERY JAR IN THE LIB DIR
for ($x = 1759; $x < 1872; $x++)
print "p4 describe -s $x > p4_desribe_$x\n";
`p4 describe -s $x > p4_desribe_$x\n`;
Obviously I changed my numeric range from 100-200 to 1759-1871, and I redirected all output to files with the change number in the name. That allowed my to grep through all the files and look for entries I was interested in.
In case anyone wants to know, my original problem was to identify files in a version control system (perforce) which had changed after a certain date - but only the ones in a particular project.
I had to do this because I forgot to label the release and was trying to separate two projects.