/^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/


##</code><code>##

     /^[+-]?(?:\d|\.\d)\d*(?:\.\d*)?(?:[Ee][+-]?\d+)?$/


##</code><code>##

#!/usr/bin/perl -wl

use strict;

my @nums = qw(
              0e0
              0
              +0
              -0
              1.
              0.14
              .14
              1.24e5
              24e5
              -24e-5
              2.3.
              2.3.4
              1..2
             );

for (@nums) {
    # Print only if the match fails

    # perlfaq4 regex
    print "1: ", $_ if ! /^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/;

    # perlfaq4 regex modified
    print "2: ", $_ if ! /^[+-]?(?:\d|\.\d)\d*(?:\.\d*)?(?:[Ee][+-]?\d+)?$/;

    # perlfaq4 decimal regex extended to match floating point
    print "3: ", $_ if ! /^[+-]?(?:\d+(?:\.\d*)?|\.\d+)([Ee][+-]?\d+)?$/;

}