The split command applied to args[0] (a1+b3-c5=4x) string uses arg[1] ([12345][+-=]) as a regexp argument for splitting the string. The regexp expression reads as "any number in 1 2 3 4 5 followed by '+' '-' or '=' symbol" The result will be a String array {"a", "b","c","4x"} whose length is, obviously, 4.