How to execute chained commands in a shell running as a child process?

Question

Following the question at How to execute a command in a shell running as a child process?, I want to execute multiple commands.

let mut child = Command::new("sh").stdin(Stdio::piped())
    .stderr(Stdio::piped())
    .stdout(Stdio::piped())
    .spawn()?;

child.stdin
    .as_mut()
    .ok_or("Child process stdin has not been captured!")?
    .write_all(b"something...")?;

let output = child.wait_with_output()?;

Is it possible to do something like this?

.write_all(b"something...")?
.write_all(b"something...")?;

Shouldn't `.write_all(b"something \n something2")?` do the trick? This has nothing do with rust, just sh. — chpio, Sep 09 '20 at 12:00
It worked @chpio, can you write it in answer, I will accept it — Harshit, Sep 09 '20 at 12:21

score 1 · Accepted Answer · edited Sep 09 '20 at 14:48

1

This is not a problem in Rust, but sh. In sh you need to separate commands by newlines ("\n"):

//...
.write_all(b"command1\ncommand2")?;
//...

this should work too:

//...
let child_stdin = child.stdin
    .as_mut()
    .ok_or("Child process stdin has not been captured!")?;

child_stdin.write_all(b"command1\n")?;
child_stdin.write_all(b"command2\n")?;
//...

edited Sep 09 '20 at 14:48

Shepmaster

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answered Sep 09 '20 at 14:35

chpio

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score 0 · Answer 2 · edited Sep 09 '20 at 13:29

Chaining method calls works for methods that, by convention, return self or &mut self. There is no guarantee that all methods do that, some simply have more useful return values. For example, write_all() returns Result<(), io::Error>, declaring that it has no useful value other than showing whether the writing succeeded or failed.

To call such a method twice, you need to save your value into a local variable:

let child_stdin = child
    .stdin
    .as_mut()
    .ok_or("Child process stdin has not been captured!")?;
child_stdin.write_all(b"something...")?;
child_stdin.write_all(b"something...")?;

How to execute chained commands in a shell running as a child process?

2 Answers2