#!/usr/bin/perl
use strict; 
use warnings;
my $str1 = "helloworld";
my $str2 = "hello";

if  ($str1 ne $str2 and $str1 =~ /\Q$str2\E/) 
{ 
    print "yes, $str2 is a substring of $str1\n"; 
}

# Note: the \Q and \E escapes are not needed in
# this exact situation. These escape characters mean
# to ignore any chars in $str2 that might otherwise
# mean something to the regex engine.

# In this simple case the \E is not needed, but 
# I would recommend a \Q...\E pair.

__END__
Prints:
yes, hello is a substring of helloworld