Logging in node.js to a file, without another module

Question

I'm running a node application as a daemon. When debugging the daemon, I need to see the output, so I'd like to redirect stdout and stderr to a file.

I'd expect I can just reassign stdout and stderr like in Python or C:

fs = require('fs');
process.stdout = fs.openSync('/var/log/foo', 'w');
process.stderr = process.stdout;
console.log('hello');

When I run the script directly, "hello" is printed to the console! Of course when I run in the background, I see output neither on the console (of course) or in /var/log/foo.

I don't want or need sophisticated logging. I just need to see the builtin messages that node already provides.

The other module hooks into node somehow. I want to know how, so I can do it myself. — Cuadue
– Cuadue, Commented Sep 18, 2013 at 21:04

SLaks · Accepted Answer · 2013-09-18 21:05:16Z

1

The console object grabs a reference to process.stdout and stderr when it is first created.
(you can see this in the source).

Re-assigning them later does not affect console.

The usual way to redirect these streams is to launch the process with the streams redirected.

Alternatively, you can overwrite the console methods and make them write to your file instead.

answered Sep 18, 2013 at 21:05

SLaks

891k182 gold badges1.9k silver badges2k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Community · Accepted Answer · 2017-05-23 12:11:08Z

0

Similar to this question, you can overwrite process.stdout.write which is called from console.log.

var fs = require('fs');
var oldWrite = process.stdout.write;

process.stdout.write = function (d) {
    fs.appendFileSync('./foo', d);
    oldWrite.apply(this, arguments);
};

console.log('hello');

edited May 23, 2017 at 12:11

CommunityBot

11 silver badge

answered Sep 18, 2013 at 21:15

matth

6,3344 gold badges40 silver badges44 bronze badges

Collectives™ on Stack Overflow

Logging in node.js to a file, without another module

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related