You will be doing yourself a huge favor if you use a module to parse HTML instead of regexes. I discussed some of the options for parsing HTML and gave some example code here: "Two classic modules are HTML::Parser and HTML::TreeBuilder, but there are several others, such as Mojo::DOM. If the input is always XHTML, there's XML::Twig and many more XML-based modules."

use warnings;
use strict;
use Data::Dump;
use Mojo::DOM;

my $html = <<'END_HTML';
<span class="remaining-data">54MB used</span>
<span class="expires-data-right-align">1.44GB remaining</span>
END_HTML

my $dom = Mojo::DOM->new($html);
for my $e ($dom->find('span[class="remaining-data"]')->each) {
    dd $e->text;
    my ($val,$unit) = $e->text =~ /([+-]?(?:\d*\.)?\d+)(MB|GB) used/
        or die "Couldn't parse '".$e->text."'";
    dd $val, $unit;
}

__END__

"54MB used"
(54, "MB")
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