I'm trying to execute a bash script from a Node application, which I have previously done successfully via:
var spawn = require('child_process').spawn;
spawn('bash', [pathToScript], {
stdio: 'ignore',
detached: true
}).unref();
It's important that I do it this way, because the script needs to continue to execute, even if/when the application is stopped.
Now, the script I need to execute requires an input value to be provided on the command line, ie.
./myScript.sh hello
But I cannot figure out how to pass this into the spawn call. I have tried the following, with no luck
var spawn = require('child_process').spawn;
spawn('bash', [pathToScript + '' + params], {
stdio: 'ignore',
detached: true
}).unref();
The second parameter in spawn is an array of arguments to pass to the command. So I think you almost have it but instead of concating the params to the path pass them in as an array:
var spawn = require('child_process').spawn;
var params = ['pathToScript','run', '-silent'];
spawn('bash', params, {
stdio: 'ignore',
detached: true
}).unref();
Related
How to execute the command npm init in the nodejs file? I want to use node. / index.js to execute the command. But what should I do if the command interacts with the user?
This code is directly stuck, and the subsequent question and answer cannot be carried out.I hope users can fill in the information normally
let exec = require('child_process').exec;
exec("npm init")
To allow users to fill in the questionnaire via the CLI, consider using the child_process module's spawn() method instead of exec().
*Nix (Linux, macOS, ... )
For example:
index.js
const spawn = require('child_process').spawn;
spawn('npm', ['init'], {
shell: true,
stdio: 'inherit'
});
Note: After the user has completed the questionnaire this example (above) creates the resultant package.json file in the current working directory, i.e. the same directory from where the node command invoked index.js.
However, If you want to ensure that package.json is always created in the same directory as where index.js resides then set the value of the cwd option to __dirname. For example:
const spawn = require('child_process').spawn;
spawn('npm', ['init'], {
cwd: __dirname, // <---
shell: true,
stdio: 'inherit'
});
Windows
If you are running node.js on Windows then you need to use the following variation instead:
script.js
const spawn = require('child_process').spawn;
spawn('cmd', ['/c', 'npm init'], { //<----
shell: true,
stdio: 'inherit'
});
This also utilizes the spawn() method, however it starts a new instance of Windows command shell (cmd). The /c option runs the npm init command and then terminates.
Cross-platform (Linux, macOS, Windows, ... )
For a cross platform solution, (i.e. one that runs on Windows, Linux, macOS), then consider combining the previous examples to produce the following variation:
script.js
const spawn = require('child_process').spawn;
const isWindows = process.platform === 'win32';
const cmd = isWindows ? 'cmd' : 'npm';
const args = isWindows ? ['/c', 'npm init'] : ['init'];
spawn(cmd, args, {
shell: true,
stdio: 'inherit'
});
Assuming there doesn't need to be any user input you could do:
let exec = require('child_process').exec;
exec("npm init -y")
i have following code on node for windows:
var spawn = require('child_process').spawn,
out = fs.openSync('./out.log', 'a'),
err = fs.openSync('./out.log', 'a');
spawn('cmd', [ '/c', 'start', '""', __dirname + tstDir + 'bin/test.bat', 'agent', ' -f ', configuration.path2lgst + 'test.conf' ], {
stdio: [ 'ignore', out, err ], // piping stdout and stderr to out.log
detached: true
}).unref();
In general i want to start a cmd which executes a .bat file that runs a process infinetly. node.js should return after this is initiated.
The problem is that what ever i try, either the cmd exits when node finished starting the cmd with the batch file or everything starts fine (like above code) but the process in node.js never returns.
Any ideas what could be done??
Cheers
Thorsten
I have an endless NodeJS script.js loop and I need this script to execute another script in background as a service which is a WebSocket service actually.
var exec = require('child_process').exec;
exec('node bgService.js &');
So now both scripts are running okay!
When I do a Ctrl+C on my script.js, the bgService.js script is also removed from memory which I don't want to.
How to run something in the background and forget ?
You can do it using child_process.spawn with detached option:
var spawn = require('child_process').spawn;
spawn('node', ['bgService.js'], {
detached: true
});
It will make child process the leader of a new process group, so it'll continue running after parent process will exit.
But by default parent process will wait for the detached child to exit, and it'll also listen for its stdio. To completely detach child process from the parent you should:
detach child's stdio from the parent process, piping it to some file or to /dev/null
remove child process from the parent event loop reference count using unref() method
Here is an example of doing it:
var spawn = require('child_process').spawn;
spawn('node', ['bgService.js'], {
stdio: 'ignore', // piping all stdio to /dev/null
detached: true
}).unref();
If you don't want to loose child's stdin output, you may pipe it to some log file:
var fs = require('fs'),
spawn = require('child_process').spawn,
out = fs.openSync('./out.log', 'a'),
err = fs.openSync('./out.log', 'a');
spawn('node', ['bgService.js'], {
stdio: [ 'ignore', out, err ], // piping stdout and stderr to out.log
detached: true
}).unref();
For more information see child_process.spawn documentation
Short answer: (tl;dr)
spawn('command', ['arg', ...],
{ stdio: 'ignore', detached: true }).unref()
unref is required to prevent parent from waiting.
docs
How to spawn this command (/usr/bin/which flac) on node.js:
var spawn = require('child_process').spawn;
var cmd = spawn('/usr/bin/which flac', parameters);
I've tried that code but its not working, assuming that parameters variables are set.
In your case, flac needs to be passed as a parameter. Try this:
var spawn = require('child_process').spawn;
var cmd = spawn('/usr/bin/which', ['flac'], {detached:true, stdio: 'inherit'})
.on('exit',function(code){
//check exit code
});
For example, running the same code with node instead of flac gives:
/usr/bin/node
I'm trying to launch a shell command from Node.js, without redirecting that command's input and output -- just like shelling out to a command using a shell script, or using Ruby's system command. If the child process wants to write to STDOUT, I want that to go straight to the console (or get redirected, if my Node app's output was redirected).
Node doesn't seem to have any straightforward way to do this. It looks like the only way to run another process is with child_process, which always redirects the child process's input and output to pipes. I can write code to accept data from those pipes and write it to my process's STDOUT and STDERR, but if I do that, the APIs force me to sacrifice some flexibility.
I want two features:
Shell syntax. I want to be able to pipe output between commands, or run Windows batch files.
Unlimited output. If I'm shelling out to a compiler and it wants to generate megabytes of compiler warnings, I want them all to scroll across the screen (until the user gets sick of it and hits Ctrl+C).
It looks like Node wants to force me choose between those two features.
If I want an unlimited amount of output, I can use child_process.spawn and then do child.stdout.on('data', function(data) { process.stdout.write(data); }); and the same thing for stderr, and it'll happily pipe data until the cows come home. Unfortunately, spawn doesn't support shell syntax.
If I want shell syntax, I can use child_process.exec. But exec insists on buffering the child process's STDOUT and STDERR for me and giving them to me all at the end, and it limits the size of those buffers (configurable, 200K by default). I can still hook the on('data') events, if I want to see the output as it's generated, but exec will still add the data to its buffers too. When the amount of data exceeds the predefined buffer size, exec will terminate the child process.
(There's also child_process.execFile, which is the worst of both worlds from a flexibility standpoint: no shell syntax, but you still have to cap the amount of output you expect.)
Am I missing something? Is there any way to just shell out to a child process in Node, and not redirect its input and output? Something that supports shell syntax and doesn't crap out after a predefined amount of output, just like is available in shell scripts, Ruby, etc.?
You can inherit stdin/out/error streams via spawn argument so you don't need to pipe them manually:
var spawn = require('child_process').spawn;
spawn('ls', [], { stdio: 'inherit' });
Use shell for shell syntax - for bash it's -c parameter to read script from string:
var spawn = require('child_process').spawn;
var shellSyntaxCommand = 'ls -l | grep test | wc -c';
spawn('sh', ['-c', shellSyntaxCommand], { stdio: 'inherit' });
To summarise:
var spawn = require('child_process').spawn;
function shspawn(command) {
spawn('sh', ['-c', command], { stdio: 'inherit' });
}
shspawn('ls -l | grep test | wc -c');
You can replace exec by spawn and use the shell syntax simply with:
const {spawn} = require ('child_process');
const cmd = 'ls -l | grep test | wc -c';
const p = spawn (cmd, [], {shell: true});
p.stdout.on ('data', (data) => {
console.log (data.toString ());
});
The magic is just {shell: true}.
I haven't used it, but I've seen this library: https://github.com/polotek/procstreams
It you'd do this. The .out() automatically pipes to the process's stdin/out.
var $p = require('procstreams');
$p('cat lines.txt').pipe('wc -l').out();
If doesn't support shell syntax, but that's pretty trivial I think.
var command_str = "cat lines.txt | wc -l";
var cmds = command_str.split(/\s?\|\s?/);
var cmd = $p(cmds.shift());
while(cmds.length) cmd = cmd.pipe(cmds.shift());
cmd
.out()
.on('exit', function() {
// Do whatever
});
There's an example in the node docs for the child_process module:
Example of detaching a long-running process and redirecting its output to a file:
var fs = require('fs'),
spawn = require('child_process').spawn,
out = fs.openSync('./out.log', 'a'),
err = fs.openSync('./out.log', 'a');
var child = spawn('prg', [], {
detached: true,
stdio: [ 'ignore', out, err ]
});
child.unref();