I'm trying to return the output of this function as a string, but it keeps returning as undefined. Where am I going wrong?
function run(cmd){
var spawn = require('child_process').spawn;
var command = spawn(cmd);
var result = '';
command.stdout.on('data', function(data) {
result += data.toString();
});
command.on('close', function(code) {
return result;
});
}
console.log(run('ls'));
Your function returns immediately after command.on statement. The return statement in your callback for the close event is returned to nowhere. The return belongs to event callback, not to run().
Put console.log call instead of return result.
Generally speaking you should write something like:
function run(cmd, callback) {
var spawn = require('child_process').spawn;
var command = spawn(cmd);
var result = '';
command.stdout.on('data', function(data) {
result += data.toString();
});
command.on('close', function(code) {
return callback(result);
});
}
run("ls", function(result) { console.log(result) });
child.stdout.on('data', data) and wondering why my output was incomplete and randomly truncated. If you're experiencing that problem store the data into a variable first which is resolved/rejected inside your child.on('close') event as in this answer. Thanks @fuwanekovar spawn = require('child_process').spawn,
command = spawn('ls', ['/tmp/']);
command.stdout.pipe(process.stdout);
The following link is exactly the same question as yours.
You can always wrap your function in a promise and return that. I find more efficient than @fuwaneko's callback solution
function run(cmd) {
return new Promise((resolve, reject) => {
var spawn = require('child_process').spawn;
var command = spawn(cmd)
var result = ''
command.stdout.on('data', function(data) {
result += data.toString()
})
command.on('close', function(code) {
resolve(result)
})
command.on('error', function(err) { reject(err) })
})
}
ping command and it didn't work. @fuwaneko's solution worked for me, however.clean way is using async/await so try like this:
const spawn = require('child_process').spawnSync;
try {
const child = spawn(cmd)
return { stdout: child.stdout.toString(), stderr: child.stderr.toString() }
} catch (error) {
console.log(error);
return error
}
async/await?
spawnSync with spawn? It is confusing because there exists a spawn method by itself.Typescript version:
(following common current async usage)
import { spawn } from 'child_process'
const run = (commandLine: string) => new Promise<string>((resolve, reject) => {
const [command, ...args] = commandLine.split(/\s+/)
const child = spawn(command, args)
const output = [] as string[]
child.stdout.on('data', chunk => output.push(chunk))
child.on('close', () => resolve(output.join('').trim()))
child.on('error', error => reject(error))
})
usage:
const branch = await run('git branch --show-current')
