#!/usr/bin/perl -w

use strict;

my $str = "x:= y + z;";

my @tokens = split /\s+|(?<=\w)(?=(?:;|:=))/, $str;

print join "\n", @tokens;

##</code><code>##

my @tokens = split /
                    \s+      # whitespace
                    |        # or
                    (?<=\w)  # after a word character
                    (?=      # before a .....
                     (?:     # non-backreferencing paranthesis (to prevent adding matches to list returned)
                      ;      # a semicolon
                      |      # or
                      :=     # colon equals; add more operators to split on after here
                     )
                    )
                   /x, $str;