Using Perl to match all words after a particular word - regex

Question

I am using Perl and need to get all domain names from http://www.malwaredomainlist.com/hostslist/hosts.txt into a flat file.
I think the easiest way to do this is to use a regular expression but I can't get my head around how to build the expression.
my code so far:
#!/usr/bin/perl
use LWP::Simple;
$url = 'http://www.malwaredomainlist.com/hostslist/hosts.txt';
$content = get $url;
open(my $fh, '>', '/home/jay/feed.txt');
#logic here
}
close $fh;
I'm not sure if I should loop over each line and perform an expression on that or if I should take the whole file as a string and work with that.

Answer 1

The page is just a text/plain document, so I think I would just copy and paste the page into my editor and remove the unwanted information. However if you would prefer a Perl program then this is all that is necessary. It uses LWP::Simple::get to fetch the text page and a regex to search it for lines starting with digits and dots, returning the second field of each
use strict;
use warnings;
use feature 'say';
use LWP::Simple qw/ get /;
my $url = 'http://www.malwaredomainlist.com/hostslist/hosts.txt';
say for get($url) =~ /^[\d.]+\s+(\S+)/gam;
or as a one-liner
perl -MLWP::Simple=get -E"say for get(shift) =~ /^[\d.]+\s+(\S+)/gam" http://www.malwaredomainlist.com/hostslist/hosts.txt

Answer 2

Unless you have a particular need, iterating by line is the way forward. Otherwise you just tie up memory unnecessarily.
However when you're fetching a url, it's a bit academic - I would suggest that fetching it to a file first isn't a bad thing though, so you can re-process it without needing to refetch.
Given source data sample:
for ( split ( "\n", $content ) ) {
next unless m/^\d/; #skip lines that don't start with a digit.
my ( $IP, $hostname ) = split;
my $domainname = $hostname =~ s/^\w+\.//r;
print $domainname,"\n";
}
This doesn't entirely work with your list though, because in that list you have a mix of hostnames and domain names, and it's not actually all that easy to tell the difference.
After all, the 'tld' at the end might be .com or it might be .org.it

Answer 3

127.0.0.1\s+(.*)
should work fine with global modifier.
Demo

Answer 4

Unless saving the list file locally is a requirement (in which case you might be better off just using wget or curl), there is no need to save it in an external file to process it line-by-line.
You can instead open a filehandle to the string itself.
In the script below, extract_hosts would work the same whether you give it a reference to a string or a filename:
#!/usr/bin/env perl
use strict;
use warnings;
use Carp qw( croak );
use LWP::Simple qw( get );
my $url = 'http://www.malwaredomainlist.com/hostslist/hosts.txt';
my $malware_hosts = get $url;
unless (defined $malware_hosts) {
die "Failed to get content from '$url'\n";
}
my $hosts = extract_hosts(\$malware_hosts);
print "$_\n" for #$hosts;
sub extract_hosts {
my $src = shift;
open my $fh, '<', $src
or croak "Failed to open '$src' for reading: $!";
my #hosts;
while (my $entry = <$fh>) {
next unless $entry =~ /\S/;
next if $entry =~ /^#/;
my (undef, $host) = split ' ', $entry;
push #hosts, $host;
}
close $fh
or croak "Failed to close '$src': $!";
\#hosts;
}
This will give you the list of hosts.

Answer 5

Code to grep the hostnames from the given file.
use LWP::Simple;
my $url = 'http://www.malwaredomainlist.com/hostslist/hosts.txt';
my $content = get $url;
my #server_names = split(/127\.0\.0\.1\s*/, $content);
open(my $fh, '>', '/home/jay/feed.txt');
print $fh "#server_names";
close $fh;

Answer 6

Here is another implementation. It uses HTML::Tiny which is part of the core so you don't have to install anything.
use HTTP::Tiny;
my $response = HTTP::Tiny->new->get('http://www.malwaredomainlist.com/hostslist/hosts.txt');
die "Failed!\n" unless $response->{success};
my #content;
for my $line ( split ( "\n", $response->{content} ) ){
next if ( $line =~ /^#|^$/);
push #content, ((split ( " ", $line ))[1]);
}
print Dumper (\#content);