Using execve(), a process can replace the program that it is currently running by a new program. Arguments to the execve() call allow the specification of the argument list (argv) and environment list for the new program. Various similarly named library functions are layered on top of execve() and provide different interfaces to the same functionality.
All of the exec() functions can be used to load a binary executable file or to execute an interpreter script. When a process execs a script, the script’s interpreter program replaces the program currently being executed by the process. The script’s interpreter is normally identified by an initial line (starting with the characters #!) in the script that specifies the pathname of the interpreter. If no such line is present, then the script is executable only via execlp() or execvp(), and these functions exec the shell as the script interpreter.
We showed how fork(), exec(), exit(), and wait() can be combined to implement the system() function, which can be used to execute an arbitrary shell command.