unshift <variable name> <word>
shift <variable name>

UNSHIFT prepends the given word (or words) to the given variable, padded with a single space. The variable name itself may not contain a leading '$'; the command uses the variable itself, not the expanded contents. If the variable does not exist, it is created containing the given word(s) (just as if ASSIGN were used).

SHIFT is the exact opposite of UNSHIFT, in that it chops off the first word in the variable. If there is only one word in the variable, the variable is deleted. Both UNSHIFT and SHIFT are functionally equivalent to the $unshift() and $shift() functions, respectively.