use Net::Telnet ();
    $t = new Net::Telnet;
    $t->open("192.168.0.90");
    $t->login("admin", "passwort");
    @lines = $t->cmd("show dsl stat");

@maxrate = grep /Current Attainable Rate/, @lines;

my $value = (split(/\s/,$maxrate[0]))[-1];

$maxrate[0] =~ s/.*?(\d+)$/$1/;

@array =~ s/.*?(\d+)$/$1/;

sub first_match ($@) {
    my ($regex, @data) = @_;
    my $result;
    for (@data) { $result = $1 and last if /$regex/ }
    return $result;
}

my $max = first_match qr/Current Attainable Rate -\s*(\d+)/, @lines;

The regular expression:

(?-imsx:.*?(\d+)$)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  .*?                      any character except \n (0 or more times
                           (matching the least amount possible))
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

Applying substitution (s///) to @array will act on scalar(@array) at skript.pl line 9.

$maxrate[0] =~ s/.*?(\d+)$/$1/;

$maxrate[0] = (split(/\s/,$maxrate[0]))[-1];