Question

I’ve a problem with exec() function under ubuntu.
Is there any possibility to go back to the main program?

example:

printf("Some instructions at beginning\n");
execlp("ls","ls", "-l", NULL);

// i want to continue this program after exec and see the text below
printf("Other instructions\n");

Answer 1

No. A successful exec call replaces the current program with another program. If you want both the parent and child to stick around, you need to call fork(2) before exec:

pid_t childpid = fork();
if(childpid < 0)
{
    // Handle error
}
else if(childpid == 0)
{
    // We are the child
    exec(...);
}
else
{
    // We are the parent: interact with the child, wait for it, etc.
}

Note that a failed exec call (e.g. the given executable doesn’t exist) does return. If exec returns, it’s always because of an error, so be prepared to handle the error.