use warnings;
use strict;

my $List1 = <<DATA;
.2
.3
.4
DATA

my $List2 = <<DATA;
.4
.5
.6
DATA

open my $in1, '<', \$List1 or die "Failed to open List1: $!";
my @data1 = grep {chomp; length} <$in1>;
close $in1;

my $hitCount = 0;

open my $in2, '<', \$List2 or die "Failed to open List2: $!";
while (<$in2>) {
    chomp;
    next unless length;

    my $data2 = $_;
    $hitCount += grep {abs ($data2 - $_) <= 0.2} @data1;
}

close $in2;

print "Found $hitCount matches\n";

##</code><code>##

Found 6 matches