Continuing on the diamond theme, I usually flag "dangerous" anything during code reviews that look like:

print "Some prompt? ";
$input = <>;
[download]

Why? Because that program works fine when you run it without command-line arguments. But what happens when some other part of the program needs a command arg for a toggle or something? Oops!

And saying "well, sometimes I want to get stuff from files instead of STDIN" doesn't fly, because then you get the extra prompts!

For me, the only proper combination is:

• print "..."; $input = <STDIN>;, or
• $input = <>;

In other words, if you're interacting, use the explicit filehandle. Otherwise, suck from diamond.

-- Randal L. Schwartz, Perl hacker