Hi

I would recommend to create the regular expression dynamically, based on the length of the input-string (or on the last "x"). It could somehow look like this:

my $s = "x12345x23x56x";

my $len = (length($s)-3)/2;
my $re = "x" . "."x$len . "x" . "."x$len . "x";   # this is the RegEx 
+you want

if ($s =~ /$re/) { print "ok\n"; } else {print "nok\n";}
[download]

HTH, Rata