uninitialized value in numeric error

[David Kenneally]

Hello-

This is a really basic question, sorry. Can anybody tell me why I get the
following error when I run this script:

"Use of uninitialized value in numeric lt (<) at ./x2 line 8"


#!/usr/bin/perl -w


opendir DIRH, "/home/dwk/test" or die "can't open it: $!\n";
@allfiles = readdir DIRH;
closedir DIRH;
foreach $temp (@allfiles) {
  if (-M $temp < "0.5") {
   print "$temp\n";
   } else {
   print "$temp is older than 12 hours\n";
     }
  }


I just want it to be able to distinguish between files that are older than
12 hours, and those that are newer (then I will build on it to do better
things than just print).

Thanks

David