I'm seeking constructive critisism on some code.

First, I don't think

  while (<>) {
      chomp;
      s/ //g;
      tr/a-z/A-Z/;
      } if (/^GRD/) {
[download]

is doing what you think it is. Ponder the difference between

  while ( ... ) { ... }
  if ( ... ) { ... }
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and

  while ( ... ) {
      ...
      if ( ... ) {
          ....
      }
  }
[download]

Next, can you explain what   @GRD = split /,"?|""?/; is supposed to be doing? It leads me to believe that there's more to your data than the sample shows. Is your data a CSV file with quoted values?

And what is   close ARGV if eof; supposed to be doing? Is there a file handle named ARGV that you opened previously? If so, that's the not the right way to test for eof.

Your field routine looks like it was written by someone who speaks C, but who hasn't yet come to terms with Perl, either in terms of control structures or in terms of how to deal with variable names. If I'm reading your intent correctly, it can be collapsed into something like

    my @GRD = split /,/;
    warn "line $.: wrong number of attributes\n"
        unless @GRD == 6;
    check($GRD[0], 1, @GRDF1);
    check($GRD[1], 2, @GRDF2);
    ...
    check($GRD[5], 6, @GRDF6);


    sub check (
        my($GRD, $col, $@GRDF) = @_;
        return if grep { $GRD eq $_ } @GRDF;
        print "line $.: \"$GRD\" is invalid in column $col\n";
    }
[download]

There are are better ways of doing this, but this gives you an example to chew on that illustrates some of the aspects of Perl that C programmers can gain great advantage in learning.

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