sufficient execution (and reading) permissions: use chmod 644 my_program.pl or at least chmod u+rx my_program.pl

I'm afraid the former won't work - you need at least 700 (most commonly 755, equivalent to 'chmod +x my_program.pl') for the file to execute.

Add a line like export PATH=".:$PATH"

And that, I'm afraid, is REALLY dangerous advice. It means that if someone creates a file called, say, "ls-l" (or "mroe", or "tarxvf", etc.) in /tmp (containing any variety of nasty surprises) and koolgirl happens to mistype "ls -l" while in that directory, she will have all of those nasty surprises to deal with. If you're going to add local dir execution, it should always be at the end of the path - never the beginning (i.e. 'export PATH=$PATH:.')