That expression permits only:
Numbers
Ext or ext
The specified punctuation
anywhere in the string. It fails to match if anything else is included.

Update: My test case is as follows: 

use strict;
use warnings;
my @strings;
$strings[0] = "44 (1234) 123398 Ext 123";
$strings[1] = "+44 (1234) 123398 Ext 123";
$strings[2] = "44 (1234) 123398 Ext 123 xxxxxxxxxxxxxxx";
$strings[3] ="416-967-1111 ext. 123 xxxxxxxxxxxxxxxxx";

my $counter=0;
for my $string (@strings)
{
        if ($string =~/^(?:Ext|\d|\)|\(|\.|\s|\+|\-)+$/i)
        {
                print "$counter good\n";
        }
        $counter++;
}

[download]

Which returns: 

0 good

[download]

It fails to match with a leading +, which I haven't got to the bottom of yet, but rejects all the wrong strings. (I'd missed out a vital |, which stopped the + matching - thanks to ysth for spotting it).

--------------------------------------------------------------

"If there is such a phenomenon as absolute evil, it consists in treating another human being as a thing."

John Brunner, "The Shockwave Rider".

In reply to Re^3: Tweak for my Perl Regex that screens for digits only by g0n
in thread Tweak for my Perl Regex that screens for digits only by hackermike

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