I forgot this one-liner, probably because I use it so much it has become almost instinctive:
% perl -cw script.pl
All it does is check for compiler errors and warnings, without running the program.
Why not just run the program? If script.pl doesn't compile, I suppose there is not much difference. Otherwise, it's a matter of "defensive programming." The check above takes one second to perform, and it can alert me to bugs that I may want to know of before ever running the program. Besides, there are times (e.g. when the coding is not yet complete) when all I want is to confirm that my code passes this first test of soundness, but not yet run the code. With a reasonably civilized editor, one can bind this capability to some convenient keyboard shortcut, so one can do the check periodically as one codes, which helps narrow down the location of errors.