I'm trying to read file.txt with some content like this:
jone
sia
alex
jad
and using node js I want to find the words that start with letter j
this is what I write:
let fs = require('fs');
fs.readFile('./file.txt', (err, info)=>{
let j;
let con = 0;
console.log(err)
if(err) return;
for (j=0; j < info.length; ++j)
if (info[j] == 10)
con++;
console.log(con)
if(info.indexOf('j') > -1){
console.log(info.toString())
}
})
I want to print the number of lines in text file and the words that start with letter j
but the counter result is 3 while it should be 4 and it prints all info:
jone
sia
alex
jad
while it should print jone and jad only
how solve this
You can use the readline build in core module and do something like this:
var rl = require('readline'), fs = require('fs')
var lineReader = rl.createInterface({ input: fs.createReadStream('file.txt') })
lineReader.on('line', function (name) {
if(name.startsWith('j'))
console.log(name)
})
See it working here
Here is your file.txt:
jone
sia
alex
jad
And here is the code:
const fs = require('fs');
const output = fs
.readFileSync('file.txt', 'utf8')
.trim()
.split('\n')
.filter(word => word.includes('j'));
console.log(output);
This will get you everything that includes 'j'
If you want something that will start with j you can write your own filter function like so:
const fs = require('fs');
const output = fs
.readFileSync('file.txt', 'utf8')
.trim()
.split('\n');
function filter(names, index, letter) {
return names.filter(word => word.charAt(index) === letter);
}
console.log('Length of originanl list: ', output.length);
console.log('Filtered List: ', filter(output, 0, 'j'));
console.log('Length of filtered list: ', filter(output, 0, 'j').length);
Live Demo Here
I suggest using the regular expressions approach.
info should be of type string, therefore it is possible for you to use the String.prototype function match(), like so:
let matches = info.match(expression);
or in your case: let matches = info.match(/\bj\w+/g); (example)
you can use regex to detect how many lines the text files has by detecting how many line breaks you have in your raw data (if possible):
let lines = info.match(/\n/g).length + 1; (example)
All these answers are incredibly over-complicated.
Simply iterate through all words and check if it start with the letter:
for (const word of wordList.split("\n")) {
if (word.startsWith("j")) console.log(`${word} start with the letter j`);
}
Related
im trying to take an array and make it line by line, and write it in a new text file using writefilesync, for example: const arr = [1,2,3], in the text file it should show:
a
b
c
const fs = require ('fs');
const tip = [1,2,3]
for (let i =0; i < tip.length; i ++) {
tip[i] = tip[i] + "<br / >";
return tip;
}
let textFile = fs.writeFileSync ('text.txt', tip, 'utf8');
the result in the text file should be line by line
1
2
3
You are almost there, try with this one:
const fs = require ('fs');
const tip = [1,2,3];
const result = tip.join('\n');
let textFile = fs.writeFileSync ('text.txt', result, 'utf8');
Here, you are creating a string from the array by joining each element using a \n sign, which represents a newline.
The error in your code was that you were adding <br /> tag to break the lines, which is an HTML tag and it would work only in the browser but not in a regular file.
Using for-loop, the above would look like this:
const fs = require ('fs');
const tip = [1,2,3];
let result = '';
for (let i = 0; i < tip.length; i++) {
result += tip[i] + '\n';
}
let textFile = fs.writeFileSync ('text.txt', result, 'utf8');
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 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');
I have a file with a list of words like this
add
blah
blahblah
undo
In other words, there's whitespace at the beginning of some of the lines.
Using node.js, I'm doing this to remove the whitespace (which works fine)
var fs = require('fs')
var array = fs.readFileSync(myfile.txt).toString().split("\n");
for(i in array){
var k = array[i].trim();
console.log(k);
}
but I would like to put the result in a new file like this
newfile.txt
var arr = ["add", "blah", "blahblah"];
Question: How to make an array in new file from a list of items
var fs = require('fs')
var inLines = fs.readFileSync('in.txt').toString().split("\n");
var trimmed = inLines.map(function (line) {
return line.trim();
});
// remove any blank lines
var noEmpties = trimmed.filter(function (line) {
return line;
});
var newData = 'var arr = ' + JSON.stringify(noEmpties) + ';\n'
fs.writeFileSync('newfile.txt', newData, 'utf8');
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);