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Re: shebang arguments

by friedo (Prior)
on Jul 02, 2008 at 18:14 UTC ( #695167=note: print w/ replies, xml ) Need Help??


in reply to shebang arguments

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:

#!/usr/bin/perl 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.


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Re^2: shebang arguments
by pc0019 (Acolyte) on Jul 02, 2008 at 20:46 UTC
    Thanks very much everyone, especially friedo for the comprehensive answer :-)

    I found the answer to '-f or -d' here:
    http://perldoc.perl.org/functions/-X.html

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