Synopsis:
   $pop(<variable name>)
   $push(<variable name> <data>)

Technical:
   These functions are used to add or remove a word from the end of a
   variable.  They are analogous to the commands of the same names; $pop()
   removes the last word from the variable and returns it, while $push()
   adds the given word to the end of the variable and returns the resulting
   contents of the variable.

Practical:
   These functions are probably the most efficient for adding data to or
   removing data from the end of a variable.  It works in the variable name
   directly, so no expansion is involved (meaning you do not give the
   variable in the $var notation, just the name alone).

   If the variable to push to does not exist, it is created.  The variable
   is deleted if the only word in it is popped off.

Returns:
   pop:  word removed
   push: variable contents after push

Examples:
   $push(blah hello there)            adds "hello there" to end of $blah
   $pop(blah)                         removes "there" from $blah

See Also:
   pop(5); push(5); shift(6); unshift(6)