/^([^.]+)\./

#!/usr/bin/perl

use warnings;
use strict;

while(my $zeile = <DATA>) {

   my @array =  ();
   @array    = split(/\./, $zeile);

   print join("\n", $array[0])."\n";

} # while
__DATA__
Auto.VW.Golf.BJ
Auto2.VW.Polo.BJ
Auto3.Audi.A5.BJ
Auto4.Audi.A4.BJ
Auto5.Audi.A3.BJ

#!/usr/bin/perl -l
use strict;
use warnings;

while my ( $line = <DATA> ) {
  my $field1 = ( split /\./, $line, 2 )[0];
  print $field1;
}

__DATA__
Auto.VW.Golf.BJ
Auto2.VW.Polo.BJ
Auto3.Audi.A5.BJ
Auto4.Audi.A4.BJ
Auto5.Audi.A3.BJ

print $array[0]."\n";

print join("\n", $array[0], $array[2]."\n"; # zB

print OUTFILE "$1;$2;$3;$4\n";

# ...
# zeilenweises lesen

chomp $line;
my @elements = split / /, $line;

# verarbeite @elements

print OUTFILE join ';', @elements;

# ...