Well, I wouldn't match "anything" but if you know what the format is roughly going to look like, you could limit it to something like this:

if ($filename =~ m#^[\w.]$#) {
  print "Ready to process $1...\n";
}
else {
  print "Skipping $1: bad characters detected\n";
  ## Log to a file, email someone, raise a ruckus, etc.
}
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