$x = '12aba34ba5';
@num = split /(a|b)+/, $x;    # @num = ('12','a','34','a','5')
print @num,$/;

@num = split /(?:a|b)+/, $x;  # @num = ('12','34','5')
print @num,$/;

##</code><code>##

@num = split /[ab]+/, $x;  # @num = ('12','34','5')
print @num,$/;