Hi, I have a situation where a C main program needs to call another C main program, my background is mostly Windows and I'm new to UNIX programming. I've read about system(), fork(), and exec() and I'm a little confused as to what the sequence of steps should be to launch another process. By the way the parent program would have to suspend execution until the child program returns and parent program would need to read the return or exit code of the child program. Thank you in advance for your help.

Should your program 1 run, while programm 2 is running? -> fork(), exec()

Else use system(), you can call any program through it.

The sequence is pipe() / fork() / exec() / waitpid(). Last call reads the exit status of the child process. Use of system() is discouraged as it's costly and resource intensive.

system() costs mainly the memory for a shell instance. It's secure when the programmer considers the environement (variables) to be unreliable/hostile.

One has to consider what's more important: simplicity of code (system()) or efficiency (fork(), exec(), ...)

Last time I checked system() was deprecated in that it uses /bin/sh -c and is a security risk due to set(u|g)id privilege escalation and environment manipulation attacks.

There's a good case that spawning a shell to execute a command is not a good idea (as shamrock noted) if a simple exec will suffice.

Hi, thank you all for your quick reply.
Hec