use strict;
use warnings;
use autodie; 


my $length;
my $file = 'the filename...';

open(my $fh, '<', $file) || die "cant open file\n"; 
while (<$fh>) {
  chomp; 
  my($target, $mirna, $score, $start) = split(/\s+/);
  print join("\t", $mirna, $target, $start, $score), "\n";
  $length = $.;
}
close $fh;