exec

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.

Exercise 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");.

Show example solution

#include <stdio.h>
#include <unistd.h>

int main(void) {
    char *args[] = {"echo", "merhaba", NULL};
    execvp("echo", args);
    printf("exec failed\n");
    return 1;
}

Test yourself

Match exec members

execl

List form
execv

Array form
execlp

PATH search list
execvp

PATH search array
What happens when execvp succeeds?
- The process terminates
- A new process is created
- The PID changes
- The process program changes
Show answer

The process program changes — exec replaces the process program; the PID stays.

args array

char *args[] = {"echo", "merhaba", ____};

Show answer

char *args[] = {"echo", "merhaba", NULL};

Next lesson: wait

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