This function waits for the child process with ID PID to terminate, returning the process ID of the deceased process. If PID does not exist, then it returns -1. The exit status of the process is contained in $?.
The flags can be set to various values which are equivalent to those used by the waitpid() UNIX system call. A value of 0 for FLAGS should work on all operating systems that support processes.
Following is the simple syntax for this function −
waitpid PID, FLAGS
This function returns -1 if process does not exist else Process ID of deceased process.