Hi guys im trying to solve the exercises from nodeschool, i started with learnyounode, people recomende it a lot for beginners, the exercise question is this:
# LEARN YOU THE NODE.JS FOR MUCH WIN!
## FILTERED LS (Exercise 5 of 13)
Create a program that prints a list of files in a given directory,
filtered by the extension of the files. You will be provided a directory
name as the first argument to your program (e.g. '/path/to/dir/') and a
file extension to filter by as the second argument.
For example, if you get 'txt' as the second argument then you will need to
filter the list to only files that end with .txt. Note that the second
argument will not come prefixed with a '.'.
Keep in mind that the first arguments of your program are not the first
values of the process.argv array, as the first two values are reserved for
system info by Node.
The list of files should be printed to the console, one file per line. You
must use asynchronous I/O.
─────────────────────────────────────────────────────────────────────────────
## HINTS
The fs.readdir() method takes a pathname as its first argument and a
callback as its second. The callback signature is:
function callback (err, list) { /* ... */ }
where list is an array of filename strings.
Documentation on the fs module can be found by pointing your browser here:
file://C:\Users\Filipe\AppData\Roaming\npm\node_modules\learnyounode\node_
apidoc\fs.html
You may also find node's path module helpful, particularly the extname
method.
Documentation on the path module can be found by pointing your browser
here:
file://C:\Users\Filipe\AppData\Roaming\npm\node_modules\learnyounode\node_
apidoc\path.html
─────────────────────────────────────────────────────────────────────────────
» To print these instructions again, run: learnyounode print
» To execute your program in a test environment, run: learnyounode run
program.js
» To verify your program, run: learnyounode verify program.js
» For help run: learnyounode help
i tried to solve the exercise doing this:
var fs = require('fs');
fs.readdir(process.argv[2],process.argv[3],function(err,list){
for(var i = 0;i<list.length;i++)
{
var fileParts = list[i].split(".");
if(fileParts[1] == process.argv[3]){
console.log(list[i] + "\n");
}
}
});
why it doesnt work, i dont know what i am doing wrong, if someone can give me a tip to solve this i appreciate a lot, since the solutions on web are quite bit strange.
Hm, I just tested your code and it actually runs fine for me. Verify returns with solved. Not sure what you are experiencing. Btw.: put in at least some error handling. Below my solution:
const fs = require('fs');
const test = '.' + process.argv[3]
fs.readdir(process.argv[2], (err, data) => {
if (err) {
console.error(err);
} else {
data.filter(file => {
if (file.substring(file.length - test.length) === test) {
console.log(file)
}
})
}
});
When I run this in bash:
mkfifo im-a-pipe && node -e '
var fs = require("fs")
var childProcess = require("child_process")
console.log("pre-open")
fs.open("im-a-pipe", "w", function(err, fd){
if(err)
throw err
console.log("opened")
})
console.log("post-open")
childProcess.exec("echo wat")
console.log("YOU CAN NOT SEE MEEE")
'
I expect the following output:
pre-open
post-open
YOU CAN NOT SEE MEEE
But instead node waits after printing the first two lines:
pre-open
post-open
I'm thinking that this probably has something to do with the pipe blocking until something opens the other side, but this behavior surprised me.
Am I missing something with how these functions are supposed to operate?
This may be a bug in your operating system or just an older version of Node. Works for me on Mac with Node 4. A co-worker was able to run it on Debian but not until he upgraded to Node 8.
That is exactly how pipes work (either named or anonymous). The writer will block until there is a reader at the other end, and a reader would block without a writer. You could say that's a fundamental principle.
Here's a little demo you can do on the command-line. You will need two terminal sessions, I'll call them A and B.
On A:
mkfifo mypipe
ls > mypipe
Session A will block. Now on session B:
cat mypipe
That should display the ls output, and unblock session A.
You can also try this by doing the cat first.
I'm pretty new to node.js and it seems fairly easy to use but when it comes to getting a value using the command line and returning that value to be used in another package or .js, it seems harder than I expected.
Long story short, I've used a npm package (akamai-ccu-purge), to enter a file to purge on the akamai network successfully.
I want to make it more dynamic though by prompting the user to enter the file they want purged and then using that in the akamai package.
After making a few tries using var stdin = process.openStdin(); I actually found another npm package called Prompt that seemed to be easier. Both ways seem to have the same problem though.
Node doesn't seem to want to stop for the input. It seems to want to automatically make the purge without waiting for input even though I've called that module first. It actually gets to the point where I should enter the file but it doesn't wait.
I am definitely missing something in my understanding or usage here, what am I doing wrong?
My code so far is:
var purgeUrl = require('./getUrl2');
var PurgerFactory = require('../../node_modules/akamai-ccu-purge/index'); // this is the directory where the index.js of the node module was installed
// area where I placed the authentication tokens
var config = {
clientToken: //my tokens and secrets akamai requires
};
// area where urls are placed. More than one can be listed with comma separated values
var objects = [
purgeUrl // I am trying to pull this from the getUrl2 module
];
// Go for it!
var Purger = PurgerFactory.create(config);
Purger.purgeObjects(objects, function(err, res) {
console.log('------------------------');
console.log('Purge Result:', res.body);
console.log('------------------------');
Purger.checkPurgeStatus(res.body.progressUri, function(err, res) {
console.log('Purge Status', res.body);
console.log('------------------------');
Purger.checkQueueLength(function(err, res) {
console.log('Queue Length', res.body);
console.log('------------------------');
});
});
});
The getUrl2 module looks like this:
var prompt = require('../../node_modules/prompt');
//
// Start the prompt
//
prompt.start();
//
// Get property from the user
//
prompt.get(['newUrl'], function (err, result) {
//
// Log the results.
//
console.log('Command-line input received:');
console.log(' http://example.com/custom/' + result.newUrl);
var purgeUrl = 'http://example.com/custom/' + result.newUrl;
console.log(purgeUrl);
module.exports = purgeUrl;
});
Thanks again for the help!
I would probably just allow getURL2 to expose a method that will be invoked in the main module. For example:
// getURL2
var prompt = require('../../node_modules/prompt');
module.exports = {
start: function(callback) {
prompt.start();
prompt.get(['newUrl'], function (err, result) {
// the callback is defined in your main module
return callback('http://example.com/custom/' + result.newUrl);
});
}
}
Then in your main module:
require('./getUrl2').start(function(purgeURL) {
// do stuff with the purgeURL defined in the other module
});
The implementation may differ, but conceptually, you need to make your second module, which requires some sort of input from the user, happen as a result of that input. Callbacks are a common way to do this (as are Promises). However, as prompt is not necessarily exposing a method that would necessitate a Promise, you can do it with plain old callbacks.
You might also want to search around for articles on writing command line tools (sometimes referenced as CLIs) or command line apps with Node. I found the following article to be helpful when trying to figure this out myself:
http://javascriptplayground.com/blog/2015/03/node-command-line-tool/
Also, the command-line-args module worked well for me (though there's a number of other modules out there to choose from):
https://www.npmjs.com/package/command-line-args
Good luck!
I am aware of tools like JSLint, but I'm not looking for style correctness, I need a tool or utility (preferably one that runs on Linux, bonus points for being in the ubuntu package manager) that can verify the syntactic correctness of a JavaScript file.
I just need to know that there are no syntax errors.
(Full disclosure, was going to put this check in a git commit hook, to ensure that syntactically incorrect JavaScript would not be committed. So it can be a style tool, but needs to be able to produce a "YES SYNTAX GOOD", or "NO SYNTAX BAD" result.)
I believe you think JSLint doesn't verify syntax, but I think it does exactly what you want. Now, for my bonus points! :-) Here is a quick example that should do everything you want, despite using JSLint.
sudo apt-get install spidermonkey-bin
wget http://www.jslint.com/fulljslint.js
mv fulljslint.js /home/admin/bin/js
then create /home/admin/bin/js/runjslint.js:
load('/home/admin/bin/js/fulljslint.js');
var body = arguments[0];
var result = JSLINT(body);
if (result) {
print('YES SYNTAX GOOD');
} else {
print('NO SYNTAX BAD');
}
print(JSLINT.report());
This file, when run using Spidermonkey, will check the syntax of Javascript data passed as a command line argument. You might not want that report at the end, thought it might be worth having for you to play with though.
acorn.js is a really small javascript parser. It throws a javascript error when it encounters a problem.
Download acorn
curl https://raw.github.com/marijnh/acorn/master/acorn.js > acorn.js
Create a runner called acornIt.js with the following contents (requires node to be installed)
var acorn = require('./acorn');
var fs = require('fs');
var fileName = process.argv[2];
var contents = fs.readFileSync(fileName);
try {
acorn.parse(contents);
console.log("YES SYNTAX GOOD");
} catch (e) {
console.log("NO SYNTAX BAD");
console.log(e); // See where the error occured
}
And run it
node acornIt.js someTestFile.js
I need in node.js function
result = execSync('node -v');
that will synchronously execute the given command line and return all stdout'ed by that command text.
ps. Sync is wrong. I know. Just for personal use.
UPDATE
Now we have mgutz's solution which gives us exit code, but not stdout! Still waiting for a more precise answer.
UPDATE
mgutz updated his answer and the solution is here :)
Also, as dgo.a mentioned, there is stand-alone module exec-sync
UPDATE 2014-07-30
ShellJS lib arrived. Consider this is the best choice for now.
UPDATE 2015-02-10
AT LAST! NodeJS 0.12 supports execSync natively.
See official docs
Node.js (since version 0.12 - so for a while) supports execSync:
child_process.execSync(command[, options])
You can now directly do this:
const execSync = require('child_process').execSync;
code = execSync('node -v');
and it'll do what you expect. (Defaults to pipe the i/o results to the parent process). Note that you can also spawnSync now.
See execSync library.
It's fairly easy to do with node-ffi. I wouldn't recommend for server processes, but for general development utilities it gets things done. Install the library.
npm install node-ffi
Example script:
var FFI = require("node-ffi");
var libc = new FFI.Library(null, {
"system": ["int32", ["string"]]
});
var run = libc.system;
run("echo $USER");
[EDIT Jun 2012: How to get STDOUT]
var lib = ffi.Library(null, {
// FILE* popen(char* cmd, char* mode);
popen: ['pointer', ['string', 'string']],
// void pclose(FILE* fp);
pclose: ['void', [ 'pointer']],
// char* fgets(char* buff, int buff, in)
fgets: ['string', ['string', 'int','pointer']]
});
function execSync(cmd) {
var
buffer = new Buffer(1024),
result = "",
fp = lib.popen(cmd, 'r');
if (!fp) throw new Error('execSync error: '+cmd);
while(lib.fgets(buffer, 1024, fp)) {
result += buffer.readCString();
};
lib.pclose(fp);
return result;
}
console.log(execSync('echo $HOME'));
Use ShellJS module.
exec function without providing callback.
Example:
var version = exec('node -v').output;
There's an excellent module for flow control in node.js called asyncblock. If wrapping the code in a function is OK for your case, the following sample may be considered:
var asyncblock = require('asyncblock');
var exec = require('child_process').exec;
asyncblock(function (flow) {
exec('node -v', flow.add());
result = flow.wait();
console.log(result); // There'll be trailing \n in the output
// Some other jobs
console.log('More results like if it were sync...');
});
Native Node.js solution is:
const {execSync} = require('child_process');
const result = execSync('node -v'); // 👈 this do the trick
Just be aware that some commands returns Buffer instead of string. And if you need string just add encoding to execSync options:
const result = execSync('git rev-parse HEAD', {encoding: 'utf8'});
... and it is also good to have timeout on sync exec:
const result = execSync('git rev-parse HEAD', {encoding: 'utf8', timeout: 10000});
This is not possible in Node.js, both child_process.spawn and child_process.exec were built from the ground up to be async.
For details see: https://github.com/ry/node/blob/master/lib/child_process.js
If you really want to have this blocking, then put everything that needs to happen afterwards in a callback, or build your own queue to handle this in a blocking fashion, I suppose you could use Async.js for this task.
Or, in case you have way too much time to spend, hack around in Node.js it self.
This is the easiest way I found:
exec-Sync:
https://github.com/jeremyfa/node-exec-sync
(Not to be confused with execSync.)
Execute shell command synchronously. Use this for migration scripts, cli programs, but not for regular server code.
Example:
var execSync = require('exec-sync');
var user = execSync('echo $USER');
console.log(user);
Just to add that even though there are few usecases where you should use them, spawnSync / execFileSync / execSync were added to node.js in these commits: https://github.com/joyent/node/compare/d58c206862dc...e8df2676748e
You can achieve this using fibers. For example, using my Common Node library, the code would look like this:
result = require('subprocess').command('node -v');
my way since 5 years is to have 2 lines ;
const { execSync } = require('child_process');
const shell = (cmd) => execSync(cmd, {encoding: 'utf8'});
Then enjoy:
shell('git remote -v')
or
out = shell('ls -l')
.. so on
I get used to implement "synchronous" stuff at the end of the callback function. Not very nice, but it works. If you need to implement a sequence of command line executions you need to wrap exec into some named function and recursively call it.
This pattern seem to be usable for me:
SeqOfExec(someParam);
function SeqOfExec(somepParam) {
// some stuff
// .....
// .....
var execStr = "yourExecString";
child_proc.exec(execStr, function (error, stdout, stderr) {
if (error != null) {
if (stdout) {
throw Error("Smth goes wrong" + error);
} else {
// consider that empty stdout causes
// creation of error object
}
}
// some stuff
// .....
// .....
// you also need some flag which will signal that you
// need to end loop
if (someFlag ) {
// your synch stuff after all execs
// here
// .....
} else {
SeqOfExec(someAnotherParam);
}
});
};
I had a similar problem and I ended up writing a node extension for this. You can check out the git repository. It's open source and free and all that good stuff !
https://github.com/aponxi/npm-execxi
ExecXI is a node extension written in C++ to execute shell commands
one by one, outputting the command's output to the console in
real-time. Optional chained, and unchained ways are present; meaning
that you can choose to stop the script after a command fails
(chained), or you can continue as if nothing has happened !
Usage instructions are in the ReadMe file. Feel free to make pull requests or submit issues!
EDIT: However it doesn't return the stdout yet... Just outputs them in real-time. It does now. Well, I just released it today. Maybe we can build on it.
Anyway, I thought it was worth to mention it.
you can do synchronous shell operations in nodejs like so:
var execSync = function(cmd) {
var exec = require('child_process').exec;
var fs = require('fs');
//for linux use ; instead of &&
//execute your command followed by a simple echo
//to file to indicate process is finished
exec(cmd + " > c:\\stdout.txt && echo done > c:\\sync.txt");
while (true) {
//consider a timeout option to prevent infinite loop
//NOTE: this will max out your cpu too!
try {
var status = fs.readFileSync('c:\\sync.txt', 'utf8');
if (status.trim() == "done") {
var res = fs.readFileSync("c:\\stdout.txt", 'utf8');
fs.unlinkSync("c:\\stdout.txt"); //cleanup temp files
fs.unlinkSync("c:\\sync.txt");
return res;
}
} catch(e) { } //readFileSync will fail until file exists
}
};
//won't return anything, but will take 10 seconds to run
console.log(execSync("sleep 10"));
//assuming there are a lot of files and subdirectories,
//this too may take a while, use your own applicable file path
console.log(execSync("dir /s c:\\usr\\docs\\"));
EDIT - this example is meant for windows environments, adjust for your own linux needs if necessary
I actually had a situation where I needed to run multiple commands one after another from a package.json preinstall script in a way that would work on both Windows and Linux/OSX, so I couldn't rely on a non-core module.
So this is what I came up with:
#cmds.coffee
childproc = require 'child_process'
exports.exec = (cmds) ->
next = ->
if cmds.length > 0
cmd = cmds.shift()
console.log "Running command: #{cmd}"
childproc.exec cmd, (err, stdout, stderr) ->
if err? then console.log err
if stdout? then console.log stdout
if stderr? then console.log stderr
next()
else
console.log "Done executing commands."
console.log "Running the follows commands:"
console.log cmds
next()
You can use it like this:
require('./cmds').exec ['grunt coffee', 'nodeunit test/tls-config.js']
EDIT: as pointed out, this doesn't actually return the output or allow you to use the result of the commands in a Node program. One other idea for that is to use LiveScript backcalls. http://livescript.net/