use strict;
my $str = 'https://www.facebook.org/hello
http://www.xxxx.wordpress.com/hello
http://www.xxxx.yyy.zzz.wordpress.com/hello';
my $regex = qr/(https?:\/\/)?([w]{3}\.)?(\w*.\w*)([\/\w]*)/mip;
my $subst = '$3';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
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