Re: Comparing adjacent lines

[The Code Captain]

Hi There

I can see a few problems straight off. You compare to $previous but you never set $previous to anything except the empty string at the start. Probably not what you intended. Also you chomp() your input after you have tokenised it. Also probably not what you intended.

I would suggest something like this (untested):

my $previous=undef;
my $ex=1;
while(<>) {
  chomp();
  @gtf=split(/\s+/, $_);
  if( ($#gtf>=9) &&
      defined($previous) &&
      ($gtf[9] eq $previous) )
  {
    $ex+=1;
  }
  else
  {
    $ex=1;
  }
  $previous=($#gtf>=9)?$gtf[9]:undef;
  $gtf[2]="ex".$ex;
}

You don't have to check the size of your input ($#gtf) if you're not concerned with it, but remember that perl's autovivification will create elements of an array for you which may not be want you want so I prefer to check the element is there before accessing it.