Interactive Programs

[DBQ]

Hey Guys,

I am was writing a shell. How do you handle programs that require input/output assuming we want to be able to pause them, background them etc.

[jpkotta]

stdin, stdout, stderr for I/O. You get this for free with any program.

Signals to pause, restart, and terminate. I believe you also get these for free (i.e. the default signal handlers do what they should). Just send the proper signals from the shell.

[DBQ]

It is not as simple as that for the applications such as pico and vi. You need to worry about the terminal state I think. Also when trying to run top on ubuntu I get a message similar to unable to open ttyd file descriptor.

[DBQ]

Perhaps you need to link up the stdin and stdout of the interactive program with to the stdin and stdout of my shell -- but the problem is, the shell runs in the background during that time.

[CptPicard]

If I were you, I'd dig into the source of some existing shells and investigate how they work. If I were writing my own, I would probably just fork the one with the cleanest source and adapt it to my needs. :)

[jpkotta]

Picard has the best advice. That's the (or rather, a) point of Free Software, right?

If I were doing this, the first scheme I would use is a fork and exec to start a new process. It seems like file descriptors are preserved across both fork and exec, so long as a certain flag is not set (FD_CLOEXEC). Thus they are probably still associated with the same tty? You probably know more about this than I do.