Nifty perl trick I learned about today

[pauamma]

Context was someone asking why

print "Hello, world!\n" && die;

doesn't output anything. Someone replied with a nifty trick to help figure this out:

perl -MO=Deparse -e 'print "Hello, world!\n" && die;'

(go ahead and try it in your Dreamhack).

Comments

[sophie]

Also, if you need to do this trick but don't know what the operator precedence is, you can add ",-p" after the "Deparse" in order to get Perl to print parentheses to show exactly how things get calculated.

One thing, btw - this won't work as a built-in code beautifier because you'll find that some string literals aren't kept; they're transformed to '???'. That's because it's a constant value that Perl optimised away for whatever reason. (The perldoc for B::Deparse explains more.)

[pne]

B::Deparse is really fun.

Have you thought about cross-posting this to command_liners?

[pauamma]

http://command-liners.dreamwidth.org/4982.html

[afuna]

Oh neat.

(What is the O for? I can find -M in man perlrun, but I can't find -O)

[alierak]

It's the argument to -M. "perldoc O" should do something.

[afuna]

Oh dur. So obvious now, thanks!