I need to pass in a text file in the terminal and then read the data from it, how can I do this?
node server.js file.txt
How do I pass in the path from the terminal, how do I read that on the other side?
This question is related to
javascript
node.js
The async way of life:
#! /usr/bin/node
const fs = require('fs');
function readall (stream)
{
return new Promise ((resolve, reject) => {
const chunks = [];
stream.on ('error', (error) => reject (error));
stream.on ('data', (chunk) => chunk && chunks.push (chunk));
stream.on ('end', () => resolve (Buffer.concat (chunks)));
});
}
function readfile (filename)
{
return readall (fs.createReadStream (filename));
}
(async () => {
let content = await readfile ('/etc/ssh/moduli').catch ((e) => {})
if (content)
console.log ("size:", content.length,
"head:", content.slice (0, 46).toString ());
})();
IMHO, fs.readFile()
should be avoided because it loads ALL the file in memory and it won't call the callback until all the file has been read.
The easiest way to read a text file is to read it line by line. I recommend a BufferedReader:
new BufferedReader ("file", { encoding: "utf8" })
.on ("error", function (error){
console.log ("error: " + error);
})
.on ("line", function (line){
console.log ("line: " + line);
})
.on ("end", function (){
console.log ("EOF");
})
.read ();
For complex data structures like .properties or json files you need to use a parser (internally it should also use a buffered reader).
You can use readstream and pipe to read the file line by line without read all the file into memory one time.
var fs = require('fs'),
es = require('event-stream'),
os = require('os');
var s = fs.createReadStream(path)
.pipe(es.split())
.pipe(es.mapSync(function(line) {
//pause the readstream
s.pause();
console.log("line:", line);
s.resume();
})
.on('error', function(err) {
console.log('Error:', err);
})
.on('end', function() {
console.log('Finish reading.');
})
);
Usign fs with node.
var fs = require('fs');
try {
var data = fs.readFileSync('file.txt', 'utf8');
console.log(data.toString());
} catch(e) {
console.log('Error:', e.stack);
}
I am posting a complete example which I finally got working. Here I am reading in a file rooms/rooms.txt
from a script rooms/rooms.js
var fs = require('fs');
var path = require('path');
var readStream = fs.createReadStream(path.join(__dirname, '../rooms') + '/rooms.txt', 'utf8');
let data = ''
readStream.on('data', function(chunk) {
data += chunk;
}).on('end', function() {
console.log(data);
});
Source: Stackoverflow.com