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I thought I was versed in pattern matching until I came across this code. After deconstructing a Perl Golf solution from mtve, I found myself unable to understand why and how 2 lines of code work.

http://terje.perlgolf.org/

#!/usr/bin/perl

for(@a=glob"{\321,.,\321}"x2) {
    $x = $_;
    for (@a) {
        $h = ~$x;
        print '*' if $_ =~ m/$h/; #Why does this line match?
        print ' ' if  $_ !~ m/$h/; #Why does this line not?

        #The next line is just for match tracking.
        $matches{"$_ =~ $h"} = $_ =~ m/$h/ ? '*' : ' ';
    }
    print "\n";
}

foreach $key(sort keys %matches) {
        print "$key    $matches{$key}\n";
}
[download]

Here's the output:

*********
* ** ** *
*********
***   ***
* *   * *
***   ***
*********
* ** ** *
*********
.. =~ ..    *
.. =~ .Ñ
.. =~ Ñ.
.. =~ ÑÑ
.Ñ =~ ..    *
.Ñ =~ .Ñ    *
.Ñ =~ Ñ.
.Ñ =~ ÑÑ
Ñ. =~ ..    *
Ñ. =~ .Ñ
Ñ. =~ Ñ.    *
Ñ. =~ ÑÑ
ÑÑ =~ ..    *
ÑÑ =~ .Ñ    *
ÑÑ =~ Ñ.    *
ÑÑ =~ ÑÑ    *
[download]

It seems odd to me that ÑÑ =~ Ñ. would match but Ñ. =~ ÑÑ would not. Here's and even simpler version that shows that Ñ =~ . matches and . =~ Ñ does not.

#!/usr/bin/perl

for(@a=glob"{\321,.,\321}"x1) {
    $x = $_;
    for (@a) {
        $h = ~$x;
        print '*' if $_ =~ m/$h/; #Why does this line match?
        print ' ' if  $_ !~ m/$h/; #Why does this line not?

        #The next line is just for match tracking.
        $matches{"$_ =~ $h"} = $_ =~ m/$h/ ? '*' : ' ';
    }
    print "\n";
}

foreach $key(sort keys %matches) {
        print "$key    $matches{$key}\n";
}
[download]

Here's the output:

***
* *
***
. =~ .    *
. =~ Ñ
Ñ =~ .    *
Ñ =~ Ñ    *
[download]

In reply to Cantor's Revenge Matching by terrencebrown

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