Execute any bash command, get the results of stdou

I would like to execute any bash command. I found Command::new but I'm unable to execute "complex" commands such as ls ; sleep 1; ls. Moreover, even if I put this in a bash script, and execute it, I will only have the result at the end of the script (as it is explain in the process doc). I would like to get the result as soon as the command prints it (and to be able to read input as well) the same way we can do it in bash.

Command::new is indeed the way to go, but it is meant to execute a program. ls ; sleep 1; ls is not a program, it's instructions for some shell. If you want to execute something like that, you would need to ask a shell to interpret that for you:

Command::new("/usr/bin/sh").args(&["-c", "ls ; sleep 1; ls"])
// your complex command is just an argument for the shell

To get the output, there are two ways:

the output method is blocking and returns the outputs and the exit status of the command.
the spawn method is non-blocking, and returns a handle containing the child's process stdin, stdout and stderr so you can communicate with the child, and a wait method to wait for it to cleanly exit. Note that by default the child inherits its parent file descriptor and you might want to set up pipes instead:

You should use something like:

let child = Command::new("/usr/bin/sh")
                .args(&["-c", "ls  sleep 1 ls"])
                .stderr(std::process::Stdio::null()) // don't care about stderr
                .stdout(std::process::Stdio::piped()) // set up stdout so we can read it
                .stdin(std::process::Stdio::piped()) // set up stdin so we can write on it
                .spawn().expect("Could not run the command"); // finally run the command

write_something_on(child.stdin);
read(child.stdout);