Programming

if i run exec1 to execute a command such as ls; ls, then is there a way i can get a return value? If i am using pipes and the child process runs the exec1 line, how can the parent process know the return value of the result of exec1?

Do you mean exec? There is a shell comand in section 1 of the manual (man pages).

Or are you trying to get the C code to create a child process whith fork() and execl()?
I am guessing you want this:
Try the system() C call, then use the macros in sys/wait.h to get your return code.

This has been answered serveral times:
How to get system() function executed cmd return value ?

I'm guessing you mean execl.

If it finds the program at all, the execl call never returns because execl tells your program to replace itself with the program you created. So naturally it can't return anything directly. Using the waitpid() call you can get a process' return statistics, like

Code:

int status;
waitpid(childpid, &status, 0);
printf("child returned %d\n", WEXITSTATUS(status));

You should always wait() for your children, if not immediately then some time or other, since they can't truly quit until you do -- just hang around taking up space in the process table.

so if i have a command and i want a child process to execute it and return the return value to the parent process, can i use:
will return_value get the return value of the command ls; ls ?

the man of system says:
system() executes a command specified in command by calling /bin/sh -c
command, and returns after the command has been completed. During exeâ
cution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT
will be ignored.

i dont understand how to return after the command has been completed...

no; that ends up as part of the status variable, which you can get with WEXITSTATUS(status).

I don't know what you expected to read from fd[0] after you closed it anyway.

fileno(stdin) is redundant. stdin is always 0. Use STDIN_FILENO (from unistd.h) if you want to be symbolic. system() does so by itself.

so now will this get the return value of the execl process?

Have you actually tried any of this code?

It might, if the amount of data is small enough. But the child might end up waiting forever for you to read the pipes, so, if you're not going to use the data the child printed to the pipe, close() them before you wait().