How to send output of shell command to client in Node.js

Question

I'd like to send output of shell command to client.

Here is the code snippet which handles POST request:

app.post('/', function(req, res) {

    console.log("request is received");
    const ps = spawn('sh', ['test.sh', req.body.code]);
    ps.stdout.on('data', (data) => {
        console.log(`stdout: ${data}`);
    });

    ps.stderr.on('data', (data) => {
        console.log(`stderr: ${data}`);
    });

    ps.on('close', (code) => {
        console.log(`child process exited with code ${code}`);
    });

    // echo incoming data to test whether POST request works
    res.status(200).json({ myReply: req.body.code });

});

How can I send stdout to client in such a case?

ralphtheninja · Accepted Answer · 2018-03-17 13:33:08Z

3

You can stream the stdout from the child process back to res. This works because ps.stdout is a readable stream and res is a writable stream.

ps.stdout.pipe(res)

answered Mar 17, 2018 at 13:33

ralphtheninja

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2 Comments

Jake Over a year ago

This only pipes stdout, not both stdout and stderr

ralphtheninja Over a year ago

So you add ps.stderr.pipe(res). However, the question specifically asks for stdout at the bottom.

jas- · Accepted Answer · 2018-03-17 13:28:56Z

First it should be noted that what you about to do is dangerous. Very dangerous.

Blindly executing a command from a client is not wise, you should sanitize both your ingress and egress data from untrusted sources.

While I am indeed making an assumption that this is not happening based on your provided example I just firmly believe you should rethink your design if this is the case.

Now that I have spoken up you should capture stdout to any array or object during the on('data', (data) => { and send it to the client on close.

let results =[]; const ps = spawn('sh', ['test.sh', req.body.code]); ps.stdout.on('data', (data) => { console.log(stdout: ${data}`); results.push(${data}); });

ps.stderr.on('data', (data) => {
    console.log(`stderr: ${data}`);
});

ps.on('close', (code) => {
    console.log(`child process exited with code ${code}`);
    res.status(200).json(results);
});

// echo incoming data to test whether POST request works
res.status(200).json({ myReply: req.body.code });`

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