my $errortype = /^(\d+)/;

  my ($errortype) = /^(\d+)/;

/^(\d+)/;

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):
----------------------------------------------------------------------
  /                        '/'
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  /                        '/'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

my ($zahl) = $zeile =~ /\s+(\d+)\s+">/

sub process_do
{
    my $self = shift;

    my %errors = (
        1 => 0,
        2 => 0,
        3 => 0,
    );
    
    while (<FILE_IN>) {
        my ($errortype) =~ /\s+(\d+)\s+">/;

        next unless $errortype;

        $errors{$errortype}++;
    }

    $self->{data}{errors} = \%errors;
}

my ($errortype) =~ /\s+(\d+)\s+">/;