Synopsis:
   push <variable name> <word>
   pop  <variable name>

Description:
   PUSH appends 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).

Aliases:
   POP is the exact opposite of PUSH, in that it pops off the last word
   in the variable.  If there is only one word in the variable, the
   variable is deleted.  Both PUSH and POP are functionally equivalent
   to the $push() and $pop() functions, respectively.

See Also:
   assign(5); shift(5); unshift(5)