while (length $source) {
  # make only one split (creating 2 parts)
  (my($rec),$source) = split /;/, $source, 2;
  # ...
}

##</code><code>##

while (my ($rec) = $source =~ /\G([^;]*)(?:;|$)/g) {
  # ...
}

##</code><code>##

use constant RE_MAGIC => bless [], 'RE_MAGIC';
use constant C_STYLE => bless [], 'C_STYLE';

{ 
  my ($re,$str);
    
  sub strtok { 
    my ($s,$pat,$opt) = @_;
    
    if (defined $s) {
      local $^W;  # in case $pat/$opt isn't a ref
      $re = ref($pat) eq "RE_MAGIC" ?
        qr/(?!\s*$)\s*(\S*)/ :
        $opt && ref($opt) eq "C_STYLE" ?
          qr/(?!(?:$pat)*$)((?:(?!$pat).)*)(?:(?:$pat)+|$)/ :
          qr/(?!(?:$pat)*$)((?:(?!$pat).)*)(?:(?:$pat)|$)/;
      $str = $s;
    }
    else {
      croak "no pattern for strtok()" if not defined $re;
    }
    
    $str =~ /\G$re/g and return $1;
    
    undef $re;
    undef $str;
  }     
}

my $rec = strtok($source, ';');
while (defined $rec) {
  # ...
  $rec = strtok();
}