You get a similar solution using a very useful idiom if you replace

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

my $len = 3;
print join ';', (split(/;/), ('') x $len)[0 .. $len-1];
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assuming that there are at most two semi-colons in the string. The focus here is the way to create the default trailing elements. This is quite useful when you create hashes, where it's imperative to not have any missing (or extra) elements. For instance:

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'
        };
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A naive

my %foo = map { split /:/ } ...;
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would've been disastrous.

lodin