use strict;
use URI::URL;
use constant BASE => 'http://www.pair.com/pair/support/index.html';

print "BASE is ", BASE, "\n\n";

while ( chomp(my $path = <DATA>) ) {
    &tryit( $path );
}

sub tryit {
    my $relative = shift;
    my $path = URI::URL->new($relative)->abs( BASE, 1 );
    print "$relative ->\n\t$path\n\n";
}

__DATA__
http://www.pair.com
/index.html
https://www.pairnic.com/faq.m
search/
library.html