I have an array of objects like below that i have to write to a file with node js, the aim is to write one item per line into one file :
cont obj = [{a:1},{b:2}]
Output file content expected :
//file.json
{a:1}
{b:2}
My code without success
jsonfile.writeFileSync(filePath, JSON.stringify(obj), 'utf-8');
/*
* [\{a:1\},\{b:2\}] <=== a string in one line with special characters
* doesn't fit on my need
*/
If someone could helps me,
Thank you.
You could simply:
const text = arr.map(JSON.stringify).reduce((prev, next) => `${prev}\n${next}`);
fs.writeFileSync(filePath, text, 'utf-8');
(That's a slight modification of #ronapelbaum approach)
You can use util.inspect and loop.
const arr = [{a:1}, {b:2}];
const filePath = "path/to/json";
for (let obj of arr)
fs.appendFileSync (filePath, util.inspect (obj) + "\n")
Or, if you'd like to accumulate the data to save on write operations:
const arr = [{a:1}, {b:2}];
const data = arr.reduce ((a, b) => a + util.inspect (b) + "\n", "");
const filePath = "path/to/json";
fs.writeFileSync (filePath, data);
The final file will fit your requirements:
{ a: 1 }
{ b: 2 }
when you're using the jsonfile library, you don't need to use JSON.stringify(obj).
in your case, you don't really want to write a valid json...
consider this:
const text = arr.reduce((txt, cur) => txt + '\n' + JSON.stringify(cur), '');
fs.writeFileSync(filePath, text, 'utf-8');
Related
I'm trying to escape quotes in txt file using node.js and regex.
My code looks like this:
const fs = require("fs");
const utf8 = require("utf8");
var dirname = ".\\f\\";
const regex = new RegExp(`(?<=".*)"(?=.*"$)`, "gm");
fs.readFile(dirname + "test.txt", (error, data) => {
if (error) {
throw error;
}
var d = data.toString();
d = utf8.encode(d)
console.log(`File: ${typeof d}`); //string
// d = `Another string\n"Test "here"."\n"Another "here"."\n"And last one here."`;
console.log(`Text: ${typeof d}`); //string
var re = d.replace(regex, '\\"');
console.log(`Result:\n${re}`);
/* Another string
"Test \"here\"."
"Another \"here\"."
"And last one here."
*/
});
The problem is:
When I remove comment from the line, everything works fine. But if i read the text from the file it doesn't want to work.
Thanks for any comments on this.
Well.. turns out the problem was in file encoding. The file was encoded in UTF-16, not in UTF-8. Node.js wasn't giving me any signs of wrong encoding, so well, nice.
I know you can read line-by-line with require('readline'), is there a good way to read a file character by character? Perhaps just use readline and then split the line into characters?
I am trying to convert this code:
const fs = require('fs');
const lines = String(fs.readFileSync(x));
for(const c of lines){
// do what I wanna do with the c
}
looking to make this into something like:
fs.createReadStream().pipe(readCharByChar).on('char', c => {
// do what I wanna do with the c
});
Simple for loop
let data = fs.readFileSync('filepath', 'utf-8');
for (const ch of data){
console.log(ch
}
Using forEach
let data = fs.readFileSync('filepath', 'utf-8');
data.split('').forEach(ch => console.log(ch)
I want to use Node.js to create a simple logging system which prints a line before the past line into a .txt file. However, I don't know how the file system functionality from Node.js works.
Can someone explain it?
Inserting data into the middle of a text file is not a simple task. If possible, you should append it to the end of your file.
The easiest way to append data some text file is to use build-in fs.appendFile(filename, data[, options], callback) function from fs module:
var fs = require('fs')
fs.appendFile('log.txt', 'new data', function (err) {
if (err) {
// append failed
} else {
// done
}
})
But if you want to write data to log file several times, then it'll be best to use fs.createWriteStream(path[, options]) function instead:
var fs = require('fs')
var logger = fs.createWriteStream('log.txt', {
flags: 'a' // 'a' means appending (old data will be preserved)
})
logger.write('some data') // append string to your file
logger.write('more data') // again
logger.write('and more') // again
Node will keep appending new data to your file every time you'll call .write, until your application will be closed, or until you'll manually close the stream calling .end:
logger.end() // close string
Note that logger.write in the above example does not write to a new line. To write data to a new line:
var writeLine = (line) => logger.write(`\n${line}`);
writeLine('Data written to a new line');
Simply use fs module and something like this:
fs.appendFile('server.log', 'string to append', function (err) {
if (err) return console.log(err);
console.log('Appended!');
});
Step 1
If you have a small file
Read all the file data in to memory
Step 2
Convert file data string into Array
Step 3
Search the array to find a location where you want to insert the text
Step 4
Once you have the location insert your text
yourArray.splice(index,0,"new added test");
Step 5
convert your array to string
yourArray.join("");
Step 6
write your file like so
fs.createWriteStream(yourArray);
This is not advised if your file is too big
I created a log file which prints data into text file using "Winston" logger. The source code is here below,
const { createLogger, format, transports } = require('winston');
var fs = require('fs')
var logger = fs.createWriteStream('Data Log.txt', {
flags: 'a'
})
const os = require('os');
var sleep = require('system-sleep');
var endOfLine = require('os').EOL;
var t = ' ';
var s = ' ';
var q = ' ';
var array1=[];
var array2=[];
var array3=[];
var array4=[];
array1[0] = 78;
array1[1] = 56;
array1[2] = 24;
array1[3] = 34;
for (var n=0;n<4;n++)
{
array2[n]=array1[n].toString();
}
for (var k=0;k<4;k++)
{
array3[k]=Buffer.from(' ');
}
for (var a=0;a<4;a++)
{
array4[a]=Buffer.from(array2[a]);
}
for (m=0;m<4;m++)
{
array4[m].copy(array3[m],0);
}
logger.write('Date'+q);
logger.write('Time'+(q+' '))
logger.write('Data 01'+t);
logger.write('Data 02'+t);
logger.write('Data 03'+t);
logger.write('Data 04'+t)
logger.write(endOfLine);
logger.write(endOfLine);
function mydata() //user defined function
{
logger.write(datechar+s);
logger.write(timechar+s);
for ( n = 0; n < 4; n++)
{
logger.write(array3[n]);
}
logger.write(endOfLine);
}
var now = new Date();
var dateFormat = require('dateformat');
var date = dateFormat(now,"isoDate");
var time = dateFormat(now, "h:MM:ss TT ");
var datechar = date.toString();
var timechar = time.toString();
mydata();
sleep(5*1000);
I need to open an existing JavaScript file, check if this string exists:
var LocalStrategy = require('passport-local').Strategy;
If it doesn't, then append it at the top with the rest of require() lines.
In another case, I need to check if that string exists, and if it does, I would like to remove just that line.
I have looked at fs.readFile, fs.writeFile, fs.open but I don't think it is capable of doing what I need. Any suggestions?
This is a simplified script:
var fs = require('fs');
var search = "var LocalStrategy = require('passport-local').Strategy;";
function append (line) {
line = line || 0;
var body = fs.readFileSync('example.js').toString();
if (body.indexOf(search) < 0 ) {
body = body.split('\n');
body.splice(line + 1,0,search);
body = body.filter(function(str){ return str; }); // remove empty lines
var output = body.join('\n');
fs.writeFileSync('example.js', output);
}
}
function remove () {
var body = fs.readFileSync('example.js').toString();
var idx = body.indexOf(search);
if (idx >= 0 ) {
var output = body.substr(0, idx) + body.substr(idx + search.length);
fs.writeFileSync('example.js', output);
}
}
I'd like to upload files on my server and name them according to their contents. This should be simple (it is in python), but I am having a hard time figuring out how to do it in Node.js.
I am using express and connect-form, which really just uses formidable. I also see that node has a library called crypto that is very similar to python's hashlib. Now I just need to understand how to stream the temp file connect-form gives me and hash it.
This is a Python/Flask(ish) implementation of what I'd like to do.
import hashlib
from Flask import request
def upload():
file = request.files['file']
hash = hashlib.sha256()
name, ext = file.filename.rsplit('.', 1)
try:
for chunk in file.chunks()
hash.update(chunk)
finally:
file.seek(0)
new_name = "%s.%s" % (hash.hexdigest(),ext)
file.save(os.path.join(UPLOAD_DIR, new_name))
I have seen a lot of these toy answers that just print out the file's name, but none that actually read and write the data.
Here it is in coffee-script in all its glory.
app.post '/upload', (request, response, next) ->
request.form.complete (error, fields, files) ->
if error
next error
else
file = files.file
[kind, extension] = file.type.split '/'
hash = crypto.createHash 'sha256'
stream = fs.createReadStream file.path,
encoding:'binary'
stream.addListener 'data', (chunk) ->
hash.update chunk
stream.addListener 'close', ->
digest = hash.digest 'hex'
new_filename = "#{digest}.#{extension}"
new_path = "#{UPLOAD_DIR}/#{new_filename}"
fs.rename file.path, new_path
response.end new_filename
Rather than hacking the hash calculation into formidable, which would likely be more efficient but far more complicated, I opted to just re-read the file from its temporary location and hash that. Then instead of pumping it like in other examples, I just renamed the temp file into its new location.
you can save a file like this:
var fs = require('fs'),
util = require('util'),
crypto = require('crypto');
// ...
req.form.complete(function (err, fields, files) {
// ...
var ext = files['content[media]']['filename'].split('.');
ext = ext[ext.length-1];
ext = ext.toLowerCase();
var newFileName = req['connection']['remoteAddress'] + req['connection']['remotePort'] + Date.now();
newFileName = crypto.createHash('md5').update(newFileName).digest("hex");
newFileName += '.' + ext;
var is = fs.createReadStream(files['content[media]']['path']);
var os = fs.createWriteStream(app.set('dataDir') + '/' + newFileName);
// copy file to public folder
util.pump(is, os, function(error) {
if (error) {
console.log("Error copying file to public ... " + error);
res.redirect("back");
return;
}
else {
// delete temp file
fs.unlinkSync(files['content[media]']['path']);
res.redirect('....');
}
});
});