>perl -wMstrict -le
"use Regexp::Common;
 ;;
 for my $t (qw(
   12.12 123.123 1 12 123 1. 12. 123. .1 .12 .123 0.1 1.0 0.0
   1234.0 1234 0.1234 .1234   -123 -.12 -0.1
   )) {
   my $ok = $t =~ m{ \A (?! .* \d{4}) $RE{num}{real} \z }xms;
   printf qq{%s '$t' \n}, $ok ? 'accept' : 'REJECT';
   }
"
accept '12.12'
accept '123.123'
accept '1'
accept '12'
accept '123'
accept '1.'
accept '12.'
accept '123.'
accept '.1'
accept '.12'
accept '.123'
accept '0.1'
accept '1.0'
accept '0.0'
REJECT '1234.0'
REJECT '1234'
REJECT '0.1234'
REJECT '.1234'
accept '-123'
accept '-.12'
accept '-0.1'