#!/usr/bin/perl -w
use strict;

foo;
&foo;

sub foo {
    print "hi\n";
}
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• won't work when you have use strict turned on
• will complain if you use -w
• and won't do anything if you don't use strict or -w

What about the second call? Well, because you precede it with an ampersand, perl knows that somewhere in the file a subroutine named foo exists. This also works if you append parens to the function name.

Jeff

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)

#!/usr/local/bin/perl

sub foo {
  $_[0] = 'b';
}

@_ = 'a';

foo();
print "@_\n";

&foo;
print "@_\n";

__END__
a
b
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There is a difference, see (tye)Re: A question of style for complete explanations.

&foo

My personal preference is to use the parentheses when calling subroutines to make things a little more readable for others.

foo();
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An additional difference is that if you call a sub with foo; (no parens) you're calling it without arguments. (Note that, as jeffa mentions, this call will only work so long as foo has already been defined)

In current versions of perl , &foo; calls foo with the current contents of @_. The difference shows up in the following code:

#!/usr/bin/perl

use strict;

sub foo {
 my $name = shift || "anonymous monk";
 uc $name;
}

print foo, "\n";

bar('arturo');

sub bar {
 print foo, "\n";
 print &foo, "\n";
}
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when run, this will print "ANONYMOUS MONK" twice, and "ARTURO" once, at the end, because the second call to foo in subroutine bar inherits the argument list passed to bar, while the first doesn't.

HTH

Philosophy can be made out of anything. Or less -- Jerry A. Fodor

An additional difference is that if you call a sub with foo; (no parens) you're calling it without arguments.

Not strictly true. Calling foo (or &foo) without arguments will pass on the current subroutine's @_ to the called subroutine.

Update:
Actually, I'm being less than 100% accurate here :)

&foo; will pass on the calling sub's @_, foo; doesn't.

Apologies for any confusion caused.

--
<http://www.dave.org.uk>

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

if(!$query->param("blah")){
   ...  #do stuff here
}
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