Consider:

use warnings;
use strict;

my @lines;

test ("No switch param:");
test ("Switch param is 0", 0);
test ("Switch param is -1", -1);

sub test {
    my $param1 = shift;
    my $switch = shift || 1;
    
    print $param1;
    print " - Switch = $switch\n";
}

[download]

Prints:

No switch param: - Switch = 1
Switch param is 0 - Switch = 1
Switch param is -1 - Switch = -1

[download]

Note that 0 || 1 is 1.

DWIM is Perl's answer to Gödel

In reply to Re: Pass an optional parameter to a subroutine by GrandFather
in thread Pass an optional parameter to a subroutine by ocs

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