use strict;
use warnings;
use Carp qw( carp );

sub get_mtime {
  my ($file) = @_;
  if (! -e $file) {
    carp "There exists no such file as '$file'";
    return undef;
  };
  if (! -f $file) {
    carp "There exists '$file' but it isn't a file.";
    return undef;
  };
  my $result = (stat $file)[9];
  carp $!
    if $!;
  $result;
};

my @files = qw(
  c:\\winnt\\cmd.exe
  c:\\winnt\\system32\\cmd.exe 
  c:\\winnt
);

for my $f (@files) {
  printf "'%s' has the mtime %s\n", $f, (get_mtime($f) || 'n/a');
};