

          fork
               Fork the current TCL process.  Fork returns zero to the
               child process and the process number of the child to
               the parent process.  If an execvp is not going to be
               performed before the forked process does output, then a
               flush should be issued against stdout, stderr and any
               other open output file before doing the fork.
               Otherwise, output from the parent process pending in
               the buffers will also be outputted by the child
               process.
