A few points:

• First, your regular expression looks fishy: /$remote_addr}/. Are you sure you need the } there?
• Your regular expression isn't anchored. It will also give a match if it finds 163.103.135.132 in the file. Or, for that matter, 63010311352132, because . has a special meaning in regular expressions. You should probably use index, or perhaps eq, depending on what is in ipfile.txt.
• You only check the first line of the file - if that is not a match, you exit the loop.
• There is no need to read in the entire file into an array, and then loop over the array. And if you loop over an array, use Perl idiom, not C idiom. Here's how I would write it:

          open my $file => "<", $ipfile or die "Open: $!";
          my $found;
          while (<$file>) {
              next if -1 == index $_ => $remote_addr;
              print "Added new guest\n";
              $found = 1;
              last; 
          }
          print "Guest not found\n" unless $found;
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  If I did need the array (in other parts of the program), I would write the loop as:

          my $found;
          foreach (@ipfconts) {
              next if -1 == index $_ => $remote_addr;
              print "Added new guest\n";
              $found = 1;
              last;
          }
          print "Guest not found\n" unless $found;
  [download]

-- Abigail