unless is a statement modifier that executes the statement if that statement is false. You are essentially going into reverse; however, unless not reverses the reverse, basically saying that it's true. That's not what you want. The correct expression to use would be unless exists. For example: 
#!/usr/bin/perl

use strict;
use warnings;

my %options;
call_view() unless exists $options{'r'};

sub call_view {
    print "doesn't exist.\n";
}

[download]
call_view() is called because $options{'r'} doesn't exist.

In reply to Re: calling a function based on a condition by Khen1950fx
in thread calling a function based on a condition by Anonymous Monk

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