my $code = <<EOT;
[head]
Head text...

[body]
Body text...

[something else]
more text..
EOT

$code =~ s/[\n ]+?(?=\S)//sg; #remove all newlines but last

formatCode($code);

sub formatCode {
    my $str = shift;

    $str =~ s{ \[ ([^\]]+) \] ([^\]]*) (?=\[|\n)}
             {<div class="$1">$2</div>}igx;

    print $str;
}