exec
- C course
- Advanced
- Lesson 8/83
- 5 min
Learn to replace a process with the exec family.
The exec family
The exec family replaces the process memory with a new program. The process ID stays the same but code, data and stack are replaced. On success, exec does not return.
Common members: execl, execv, execlp, execvp. execvp searches the PATH variable; you just give the command name. For example, execvp("echo", args) replaces the process with echo. On failure it returns -1.
Why exec with fork?
Since exec replaces the process, calling it alone loses the original program. So you typically fork a child, call exec in the child, and the parent continues its own work.
This fork-exec pattern is the standard way to run programs in UNIX. Shells do this for every command: fork → child exec → parent wait. The shell keeps running while the child executes the command.
Practice Run echo with execvp
Define the array char *args[] = {"echo", "merhaba", NULL};. Replace the process with execvp("echo", args);. On failure print printf("exec failed\n");.
Starter code
#include <stdio.h>
#include <unistd.h>
// Define args array
// Call execvp
// Print on failure
int main(void) {
return 0;
}Sample solution
#include <stdio.h>
#include <unistd.h>
int main(void) {
char *args[] = {"echo", "merhaba", NULL};
execvp("echo", args);
printf("exec failed\n");
return 1;
}Expected output
merhaba
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match exec members
| Term | Meaning |
|---|---|
execl |
List form |
execv |
Array form |
execlp |
PATH search list |
execvp |
PATH search array |
2 What happens when execvp succeeds?
- The process terminates
- A new process is created
- The PID changes
- The process program changes Correct answer
Explanation: exec replaces the process program; the PID stays.
3 args array
char *args[] = {"echo", "merhaba", ____};char *args[] = {"echo", "merhaba", NULL};Explanation: The args array must end with NULL.