They're similar, but not exactly the same. Putting -w in the command line (or the shebang) will turn on warnings globally, for all the Perl code loaded by that process.
On the other hand, use warnings is a "lexical pragma," and only applies in the block in which it's used. If you put it at the top of a script or module, then it will apply for that entire file (this is called file scope.) Inside a block, it applies only for that block:
print "no warnings out here!" . $undef_var;
use warnings; # now warnings are turned on
print "this will warn" . $undef_var;
# now warnings are off again.
(Note: Try running that with and without -w to see the difference.
Typically, it's a good idea to use warnings in your file scope, which allows you to occasionally turn them off in small blocks (using no warnings) if you absolutely must do something that will generate a warning. See perllexwarn for the gory details.
And what are things like the '-w' called (eg the -f or -d to specify file or directory)?
Those are called command-line switches or arguments, and perl's are all documented in perlrun.
Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
Read Where should I post X? if you're not absolutely sure you're posting in the right place.
Please read these before you post! —
Posts may use any of the Perl Monks Approved HTML tags:
You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
- a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
Link using PerlMonks shortcuts! What shortcuts can I use for linking?
See Writeup Formatting Tips and other pages linked from there for more info.
| & || & |
| < || < |
| > || > |
| [ || [ |
| ] || ] ||