Writing subroutines
Writing subroutines is easy:

    sub log {
        my $logmessage = shift;
        print LOGFILE $logmessage;
    }

What's that "shift"? Well, the arguments to a subroutine are available
to us as a special array called @_ (see perlvar for more on that). The
default argument to the "shift" function just happens to be @_. So "my
$logmessage = shift;" shifts the first item off the list of arguments
and assigns it to $logmessage.

We can manipulate @_ in other ways too:

    my ($logmessage, $priority) = @_;       # common
    my $logmessage = $_[0];                 # uncommon, and ugly

Subroutines can also return values:

    sub square {
        my $num = shift;
        my $result = $num * $num;
        return $result;
    }

For more information on writing subroutines, see perlsub.
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