Comparing Perl Patterns Using Arrays

Question

I have a strange problem when matching a template.

Consider the Perl code below

#!/usr/bin/perl -w use strict; my @Array = ("Hello|World","Good|Day"); function(); function(); function(); sub function { foreach my $pattern (@Array) { $pattern =~ /(\w+)\|(\w+)/g; print $1."\n"; } print "\n"; } __END__ 

Expected result should be

---

  Hello
 Good

 Hello
 Good

 Hello
 Good

---

But I get

  Hello
 Good

 Use of uninitialized value $ 1 in concatenation (.) Or string at D: \ perlfiles \ problem.pl li
 ne 28.
 Use of uninitialized value $ 1 in concatenation (.) Or string at D: \ perlfiles \ problem.pl li
 ne 28.

 Hello
 Good

What I observed was that the pattern matched the alternative.
Can someone explain to me what the problem is with this code. To fix this, I changed the function subroutine to something like this:

 sub function { my $string; foreach my $pattern (@Array) { $string .= $pattern."\n"; } while ($string =~ m/(\w+)\|(\w+)/g) { print $1."\n"; } print "\n"; } 

Now I get the output as expected.

Answer 1

This is the global /g modifier that works. It remembers the position of the last pattern match. When it reaches the end of the line, it begins.

Remove the /g modifier and it will act as you expect.