Use of uninitialized value in numeric comparison (<=>) error

[Win]

Dear Monks,

What sort of reasons could there be for the following error message?

Use of uninitialized value in numeric comparison (<=>) at Permanent.pl
+ line 54, <DATA> line 164.


  my @sorted_files =
      map  { $_->[0] }  # Error message applies here (line 54)
    sort { $a->[1] <=> $b->[1] or $a->[2] <=> $b->[2] }
      map  { [ $_, [stat]->[10], [stat]->[9] ] }  
        @files;

[McDarren]

#!/usr/bin/perl -w
use strict;
use Data::Dumper::Simple;

# Your code goes here

print Dumper(@files);

I'd say that there is a very good chance that the output of that will give you your answer.

[davidrw]

can you use Data::Dumper to see which is the offending file? I guess it means that there's a file where the mtime or ctime is empty... (Update {after reading McDarren's reply} Probably see that one of the elements in @files is undef OR one of the elements in @files is a file that does not exist/can't be stat'd)

use Data::Dumper;
print Dumper [  map { [ $_, [stat]->[10], [stat]->[9] ] } @files  ];

Also note that while it said "line 54", lines 54,55,56 (which has the <=>),57 are all the same statement.

[Win]

$VAR1 = [
          [
            'Run_in_background_P.pl',
            undef,
            undef
          ],
          [
            'Run_in_background_Q.pl',
            undef,
            undef
          ]
        ];

So why won't the network drive allow perl to access these attributes of the files?

[davidrw]

Are those two files in the current directory (the directory that the script is being run from -- see Cwd to print it out)? If no, it's not going to find them and you'll need to specify a (relative or absolute) path.

-f || die "'$_' does not exist" for @files;

[japhy]

In addition, I would suggest changing [ $_, [stat]->[10], [stat]->[9] ] to [$_, (stat)[10,9]], as it a) saves a call to stat(), and b) uses a list slice rather than two anonymous array refs.