C:\Renee>perl -Mwarnings -le "my $var = 'test123'; print 'no' unless($var =~ /^\d+$/);"
no

tina@lugosi:~/server$ perl -wle'
my $var = 23;
print "gleich" if $var == "2"'
tina@lugosi:~/server$ 

sub berechne_binom_reihe{
    use bigint;
    my $length = shift;
    return [] unless $length =~ /^[+]?\d+$/ and $length > 0;
    my @content = (1);
    my ($mid, $m2);
    for my $row (2 .. $length){
        $mid = $row - 1 >> 1;
        $r2 = $row - 2;
        $content[$_ - 1] += $content[$_] for 1 .. $mid;
        $content[$r2 - $_] = $content[$_ - 1] for 1 .. $mid;
        unshift @content, 1;
    }
    return \@content;
}