I am running this on Ubuntu and have tried many variations of exec/spawn functions (and their sync counterparts) and none of them can show me an output for bash 'history' command. One scenario is following:
const { spawnSync} = require('child_process');
const child = spawnSync('history', { shell: "/bin/bash" });
console.log('error: ', child.error);
console.log('stdout: ', child.stdout.toString());
console.log('stderr: ', child.stderr);
It does not show any errors and output is empty. I think this question has more to do with 'specialty' or category of the history command than nodejs's function since they work fine for normal commands like ls, pwd, whoami, etc work fine. I have looked at my .bash_history file and its filled with history so that's not the issue.
Another problem that might be similar is ll command also fails even though I have set bash as shell. But for ll, it does return an error:
/bin/bash: ll: command not found
Just to be sure, I tried running ll command in bash it worked just fine. What am I missing here?
edit: I have done some more testing it seems more like a bash thing than a node thing. When I simply write the history command, bash prints results but when I do bash -c history, it does not show any output but also no error.
.
You need to subscribe to messages from child process
child.on('error', (err) => {
});
child.stderr.on('data', (data) => {
});
child.on('exit', (code, signal) => {
});
Related
I know this question has been asked many times but I have tried most of the methods and they just don't work for me.
So here is my problem, I have a simple bash script like this
#!/bin/bash
echo "Username: $1";
echo %DATABASE_URL%;
I want to run this script in a separate process. so if the parent process gets killed during my script being excused it still continues running.
Here is my nodejs code
const child = spawn('bash', [`script.sh`, 'test'], {
detached: true,
cwd: process.cwd(),
detached: true,
stdio: "inherit",
DATABASE_URL: 'test'
}, function (err, stdout, stderr) {
// Node.js does not invoke this
console.log(stdout);
stdout.on("data", data => {
console.log('Output of script execution');
});
stderr.on("data", data => {
console.log('an error with file system');
});
});
child.unref();
child.on('exit', (code) => {
console.log("Child exited");
});
So I know that my script returns some output and should run callback but it does not run it. It directly jumps to the on.('exit') callback which confuses me.
Also it worth mentioning that I am testing the code on windows and bash script.sh 'test' works if I run it on cmd.
Posts I have tried:
How to run shell script file using nodejs?
Execute script from Node in a separate process
Bash Script : what does #!/bin/bash mean?
and many of the existing weblogs that explains the same.
When i run this pidof command by hand, it works. Then put into my server.js.
// send signal to start the install script
var spw = cp.spawn('/sbin/pidof', ['-x', 'wait4signal.py', '|', 'xargs', 'kill', '-USR1']);
spw.stderr.on('data', function(data) {
res.write('----- Install Error !!! -----\n');
res.write(data.toString());
console.log(data.toString());
});
spw.stdout.on('data', function(data) {
res.write('----- Install Data -----\n');
res.write(data.toString());
console.log(data.toString());
});
spw.on('close', function(data) {
res.end('----- Install Finished, please to to status page !!! -----\n');
console.log('88');
});
In the web i only see "----- Install Finished, please to to status page !!!". My install script seems never get this USR1 signal. Anything wrong please ?
The problem is that you have two separate commands. You are piping the output of your /sbin/pidof command to the input stream of your xargs command. If you are using spawn (rather than exec, which a string exactly as you would write on the command line), you need to spawn one process per command.
Spawn your processes like this:
const pidof = spawn('/sbin/pidof', ['-x', 'wait4signal.py']);
const xargs = spawn('xargs', ['kill', '-USR1']);
Now pipe the output of the first process to the input of the second, like so:
pidof.stdout.pipe(xargs.stdin);
Now you can listen to events on your xargs process, like so:
xargs.stdout.on('data', data => {
console.log(data.toString());
});
I need to use node to generate diffs of some files. I have tried the diff npm package, and while that works great it is much less performant than the version of diff you will find in /usr/bin/.
When I try to use exec to run the diff command it always errors.
var childProcess = require('child_process');
var cmd = "diff /path/to/file1.txt /path/to/file2.txt";
childProcess.exec(cmd, (error, stdout, stderr) => {
if(error) {
console.log(error);
} else {
console.log(stdout);
}
});
The output:
{ [Error: Command failed: /bin/sh -c diff /path/to/file1.txt /path/to/file2.txt
]
killed: false,
code: 1,
signal: null,
cmd: '/bin/sh -c diff /path/to/file1.txt /path/to/file2.txt' }
If I run the command on the command line myself it works fine.
I've tried running /usr/bin/diff instead of just diff.
I've tried various different forms of quoting things.
Every other command I have tried, using the exact same files, has worked. cat, wc, etc.
Any thoughts?
Welp, I am answering my own question.
The diff command returns a failure exit code if it finds a difference. Therefore the console.log(stdout) call was never being reached.
If I ignore the error, everything works.
var childProcess = require('child_process');
var cmd = "diff /path/to/file1.txt /path/to/file2.txt";
childProcess.exec(cmd, (error, stdout, stderr) => {
console.log(stdout);
});
works like a charm.
I'd like to use the execSync method which was added in NodeJS 0.12 but still have the output in the console window from which i ran the Node script.
E.g. if I run a NodeJS script which has the following line I'd like to see the full output of the rsync command "live" inside the console:
require('child_process').execSync('rsync -avAXz --info=progress2 "/src" "/dest"');
I understand that execSync returns the ouput of the command and that I could print that to the console after execution but this way I don't have "live" output...
You can pass the parent´s stdio to the child process if that´s what you want:
require('child_process').execSync(
'rsync -avAXz --info=progress2 "/src" "/dest"',
{stdio: 'inherit'}
);
You can simply use .toString().
var result = require('child_process').execSync('rsync -avAXz --info=progress2 "/src" "/dest"').toString();
console.log(result);
Edit: Looking back on this, I've realised that it doesn't actually answer the specific question because it doesn't show the output to you 'live' — only once the command has finished running.
However, I'm leaving this answer here because I know quite a few people come across this question just looking for how to print the result of the command after execution.
Unless you redirect stdout and stderr as the accepted answer suggests, this is not possible with execSync or spawnSync. Without redirecting stdout and stderr those commands only return stdout and stderr when the command is completed.
To do this without redirecting stdout and stderr, you are going to need to use spawn to do this but it's pretty straight forward:
var spawn = require('child_process').spawn;
//kick off process of listing files
var child = spawn('ls', ['-l', '/']);
//spit stdout to screen
child.stdout.on('data', function (data) { process.stdout.write(data.toString()); });
//spit stderr to screen
child.stderr.on('data', function (data) { process.stdout.write(data.toString()); });
child.on('close', function (code) {
console.log("Finished with code " + code);
});
I used an ls command that recursively lists files so that you can test it quickly. Spawn takes as first argument the executable name you are trying to run and as it's second argument it takes an array of strings representing each parameter you want to pass to that executable.
However, if you are set on using execSync and can't redirect stdout or stderr for some reason, you can open up another terminal like xterm and pass it a command like so:
var execSync = require('child_process').execSync;
execSync("xterm -title RecursiveFileListing -e ls -latkR /");
This will allow you to see what your command is doing in the new terminal but still have the synchronous call.
Simply:
try {
const cmd = 'git rev-parse --is-inside-work-tree';
execSync(cmd).toString();
} catch (error) {
console.log(`Status Code: ${error.status} with '${error.message}'`;
}
Ref: https://stackoverflow.com/a/43077917/104085
// nodejs
var execSync = require('child_process').execSync;
// typescript
const { execSync } = require("child_process");
try {
const cmd = 'git rev-parse --is-inside-work-tree';
execSync(cmd).toString();
} catch (error) {
error.status; // 0 : successful exit, but here in exception it has to be greater than 0
error.message; // Holds the message you typically want.
error.stderr; // Holds the stderr output. Use `.toString()`.
error.stdout; // Holds the stdout output. Use `.toString()`.
}
When command runs successful:
Add {"encoding": "utf8"} in options.
execSync(`pwd`, {
encoding: "utf8"
})
How can I run a command line and get the outputs as soon as available to show them somewhere.
For example if a run ping command on a linux system, it will never stop, now is it possible to get the responses while the command is still processing ?
Or let's take apt-get install command, what if i want to show the progress of the installation as it is running ?
Actually i'm using this function to execute command line and get outputs, but the function will not return until the command line ends, so if i run a ping command it will never return!
var sys = require('sys'),
exec = require('child_process').exec;
function getOutput(command,callback){
exec(
command,
(
function(){
return function(err,data,stderr){
callback(data);
}
}
)(callback)
);
}
Try using spawn instead of exec, then you can tap into the stream and listen to the data and end events.
var process = require('child_process');
var cmd = process.spawn(command);
cmd.stdout.on('data', function(output){
console.log(output.toString()):
});
cmd.on('close', function(){
console.log('Finished');
});
//Error handling
cmd.stderr.on('data', function(err){
console.log(err);
});
See the Node.js documentation for spawn here: https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options