my @col = split /;/;
push @col, '' for @col .. 2;
print join ';', @col;

##</code><code>##

my $len = 3;
print join ';', (split(/;/), ('') x $len)[0 .. $len-1];

##</code><code>##

my %foo =
  map { (split /:/, $_, 2)[0, 1] } # Implicit "default" undef.
  qw/
    foo:bar
    baz
    zip:zap:zoom
  /
;

use Data::Dumper;
print Dumper(\%foo);

__END__
$VAR1 = {
          'baz' => undef,
          'foo' => 'bar',
          'zip' => 'zap:zoom'
        };

##</code><code>##

my %foo = map { split /:/ } ...;