use strict;
my $str = '// Valid
a-a.domain.com
1a.domain.com
a1.domain.com
a.domain.com
domain.com
10.10.10.11
// Invalid
-a.domain.com
a-.domain.com
// Valid
cname.do-main.com
cname.1domain.com
cname.domain1.com
// Invalid
cname.-domain.com
cname.domain-.com
// Valid
cname.domain.tld
cname.domain.co
cname.domain.tld1
cname.domain.tld-1
// Invalid
cname.domain.1tld
cname.domain.tld-
cname.domain.-tld';
my $regex = qr/^((([a-z\d](-?[a-z\d]){0,62})\.)*(([a-z\d](-?[a-z\d]){0,62})\.)([a-z](-?[a-z\d]){1,62})|((\d{1,3}\.){3}\d{1,3}))$/mp;
if ( $str =~ /$regex/g ) {
print "Whole match is ${^MATCH} and its start/end positions can be obtained via \$-[0] and \$+[0]\n";
# print "Capture Group 1 is $1 and its start/end positions can be obtained via \$-[1] and \$+[1]\n";
# print "Capture Group 2 is $2 ... and so on\n";
}
# ${^POSTMATCH} and ${^PREMATCH} are also available with the use of '/p'
# Named capture groups can be called via $+{name}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html