Just slightly modified the previous post:

use strict;

while (defined(my $data = <DATA>)) {
  chomp $data;
  print "Got: ", $data, "\n";
  
  
  if ($data =~ 
    /[-+]?\d+|      # optional sign followed by whole number or
    [-+]?\d{0,3}    # optional sign followed by at most 3 digits
    (\.\d{1, 3})?    # followed by decimal point, and finally by at mo
+st 3 digits
    /x)
  {
        print "GOOD\n";
  } 
  else 
  {
        print "BAD\n";
  }
}

__DATA__
12.12
123.123
0.1
1234.0
1234
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