A few options (your question wasn't specific enough as to narrow down what you're after):

perl -MLWP::Simple=getprint -e 'getprint("http://perlmonks.org");' >fi
+lename_source.html
[download]

...or...

mojo get perlmonks.org >filename_source.html
[download]

...or...

perl -Mojo -E 'say g("perlmonks.org")->dom->html'
[download]

The first construct requires LWP::Simple, and the second and third, Mojolicious (which is probably only advisable if you have some other reason to have it on your system).

If you're on a Unix/Linux system you might already have curl installed.

If you want to incorporate it into a larger script:

use strict;
use warnings;
use LWP::Simple qw(get);
my $raw_page = get( 'http://perlmonks.org' );
open my $html_ofh, '>', 'filename.txt' or die $!;
print {$html_ofh} $raw_page;
close $html_ofh or die $!;
[download]

Other notables include WWW::Mechanize, LWP::UserAgent, WWW::Mechanize::Firefox, ... and a whole bunch of HTML parsers and link extractors that you can find by visiting your favorite CPAN search tool.