append - Append to variable
append varName ?value value value ...?
Append all of the value arguments to the current value of
variable varName. If varName doesn't exist, it is given a
value equal to the concatenation of all the value arguments.
This command provides an efficient way to build up long
variables incrementally. For example, ``append a $b'' is
much more efficient than ``set a $a$b'' if $a is long.
append, variable