wait -- wait for child process

wait i waits for the completion of child process with process id i.
wait f waits for the input file to have some input ready.
wait s waits for at least one of the files in the list s of input files to be ready, and return the list of positions corresponding to ready files.
wait v checks whether the processes whose id's are in the list v of integers have terminated, and returns a list containing the status codes for those processes that have terminated. A value of -1 in the list indicates an error for that process id, and a value of -2 in the list indicates that the process is still running.