Well. What happened when you tried it?

Are you really so lazy that you cannot run a two line script to see if it works or not?

And then read perldoc perlsub for further information.

The sub will be used no matter which line goes first. For evidence just reverse the comparison in the sub body.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

#!/usr/bin/perl

use strict;
use warnings;

my_sub();   # works
# my_sub;   # fails "Bareword not allowed..."

print qq{done};

sub my_sub { print qq{here\n} };
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#!/usr/bin/perl

use strict;
use warnings;

sub my_sub { print qq{here\n} };

my_sub();   # works
my_sub;     # now works too

print qq{done};
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I reckon a good bet, in these circumstances, is to always use the parens.

I reckon a good bet, in these circumstances, is to always use the parens.

Good advise but not applicable when using sort as sort only requires the name of the sub to use as a callback whereas with parentheses tells perl to run the sub.

$ perl -le'
my @x = qw[
    one
    two
    three
    four
    ];
sub compare { $a cmp $b }
print for sort compare @x;
'
four
one
three
two
$ perl -le'
my @x = qw[
    one
    two
    three
    four
    ];
sub compare { $a cmp $b }
print for sort compare() @x;
'
Array found where operator expected at -e line 9, at end of line
        (Missing operator before ?)
syntax error at -e line 9, near ") @x"
Execution of -e aborted due to compilation errors.
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Update: Had parentheses in wrong place ... oops.