while ($firstrow =~ /(<\w>)/g) {
    push @columnpos, pos($firstrow) - length($1);
}
[download]

You could use a look-ahead to avoid doing the capture, length and subtraction.

push @columnpos, pos $firstrow while $firstrow =~ m{(?=<\w>)}g;
[download]

I hope this is of interest.

Cheers,

JohnGG