Spawn node child_process with named pipe as stdin

Question

Say I have a named pipe on linux:

mkfifo lk.log

From the command line, I can do this to print out anything written to the name pipe file.

node monitor.js < lk.log

and pretend this is what the script looks like

// monitor.js

process.stdin.resume();
process.stdin.setEncoding('utf8');

// read data from stdin
process.stdin.on('data', function(chunk) {
    console.log(chunk);
});

How could I do this within node using child_process.spawn?

child_process.spawn('node', ['monitor.js'])...

score 1 · Answer 1 · answered Mar 25 '13 at 21:12

1

The easiest way would be to use exec():

var exec = require('child_process').exec;

exec('node monitor.js < lk.log', function(err, stdout, stderr) {
  ...
});

A more elaborate way would be to open the named pipe in node and pass it as stdin to the process you're spawning (see the option stdio for spawn).

answered Mar 25 '13 at 21:12

robertklep

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`child_process.exec` does not help me because it waits for the child process to terminate before being able to read from child's stdout. – Blake Regalia Mar 25 '13 at 21:23
Oops, you are correct. I guess checking out the stdio option for spawn is your only option. – robertklep Mar 25 '13 at 21:25

score 1 · Accepted Answer · answered Mar 25 '13 at 22:45

1

The answer is to use fs.open and the stdio options in child_process.spawn as such:

var spawn = require('child_process').spawn;

var fd_stdin = fs.openSync('lk.log', 'r');
spawn('node', ['monitor.js'], {
    stdio: [fd_stdin, 1, 2];
});

answered Mar 25 '13 at 22:45

Blake Regalia

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score 0 · Answer 3 · edited May 23 '17 at 12:12

From Ben Noordhuis (Core Node contributor) - 10/11/11

Windows has a concept of named pipes but since you mention mkfifo I assume you mean UNIX FIFOs.

We don't support them and probably never will (FIFOs in non-blocking mode have the potential to deadlock the event loop) but you can use UNIX sockets if you need similar functionality.

https://groups.google.com/d/msg/nodejs/9TvDwCWaB5c/udQPigFvmgAJ

For unix sockets, see: https://stackoverflow.com/a/18226566/977939

Spawn node child_process with named pipe as stdin

3 Answers3