my $i = "l-12345.in.some.domain.com/blargh/index.html";
my ($result) = $i =~ m|([^./]+)\.com|;
print $result;

# if you want to allow several endings like .com .gov etc

my ($result) = $i =~ m#([^./]+)\.(?:com|org|gov|edu|etc)#;