Rather than getpos() and setpos(), I think you may have better luck with tell() and seek().

Maybe this (very contrived) example will give you ideas.

use strict;
use warnings;
use IO::File;
use IO::Seekable;

my $file = 'whatever.fil';

$/ =';';

my  $fh = new IO::File;
if ($fh->open("< $file")) {
    my $last = 0;
    while (<$fh>){
       if ($_ =~ m|([^/]+/)|){
           $fh->seek($last+$+[0],0);
           print $1,"\n";
       }else{
           print "$_\n";
       }
       $last = $fh->tell;
    }
    $fh->close;
}else{
    die "$file not found. $!\n";
}
[download]

Minor update to remove some unnecessary cruft.