How do you execute one program from within another?

The system calls used for low-level process creation are execlp() and execvp(). The execlp call overlays the existing program with the new one , runs that and exits. The original program gets back control only when an error occurs.

execlp(path,file_name,arguments..); //last argument must be NULL

A variant of execlp called execvp is used when the number of arguments is not known in advance.

execvp(path,argument_array);  //argument array should be terminated by NULL