Sure, you can do it like this, no need for eval here.

What happened when you tried?

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

package Fyp::Security;

sub log {
    my $arg = shift;
    print $arg;
};

package main;

my $experiment_name = 'foo';
my $dirname = "/experiments/$experiment_name";

Fyp::Security::log( "Creating dir $dirname\n" );
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Interpolation - just like concatenation, i.e. "Creating dir " . $dirname . "\n" - happens at runtime, so you can arbitrarily "chain" interpolations  (if that's what your question is...)