Look at the following code fragment and try and guess what the output will be: 
use strict;
my $foo = "Hello World!";
_Printer(0, 1, 2, 3, ($foo =~ m/zoom/), 5);

sub _Printer
{
  my $foo;
  my $i = 0;

  while (scalar(@_)) {
    $foo = shift;
    print "$i: $foo\n";
    $i++;
  }
}

[download]
If you thought the output should look like the following, you're wrong: 
0: 0
1: 1
2: 2
3: 3
4: 
5: 5

[download]
The actual output (on my 5.6 Linux version of perl) is the following: 
0: 0
1: 1
2: 2
3: 3
4: 5

[download]
Apparently, Perl doesn't pass in a false or undef value for a failed regular expression match; instead, it completely ignores the argument. A passing regex match does get passed in, with a value of 1.

Anybody want to take a shot at explaining this?

-Ton

-----
Be bloody, bold, and resolute; laugh to scorn
The power of man...

In reply to Passing match regexs as arguments to subroutines by ton

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.