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fs.writeFile not overwriting file

Posted by: admin November 29, 2017 Leave a comment

Questions:

I am using node-crontab to run the script. fs.writeFile overwrite first time the loop runs but after that is appending data. I have tried deleting the file before writing but is doing the same, deletes it the first time but in the subsequent runs start to append. What should I do?

This is the script: I ommited some environment variables…

var jobId = crontab.scheduleJob('* * * * *', function() {
//Gettting  system date and adding leading zeros when are single digits.  I need this to build the get request with date filters.

    var d = new Date();
    var nday = d.getDate();
    var nmonth = d.getMonth();
    var nhour = d.getHours();
    var nmin = d.getMinutes();

    var nfullyear = d.getFullYear();
    if (nday < 10) {
        nday = '0' + nday;
    };
    var nmin = nmin - 1;
    if (nmin < 10) {
        nmin = '0' + nmin;
    };
    if (nhour < 10) {
        nhour = '0' + nhour;
    };

    var nmonth = nmonth + 1;
    if (nmonth < 10) {
        nmonth = '0' + nmonth;
    };

    var options = {
        url: 'https://[email protected]/v1/gpsdata' + '?fromdate=' + nfullyear + '-' + nmonth + '-' + nday + 'T' + nhour + '%3a' + nmin + '%3a' + '00',
        method: 'GET',
        rejectUnauthorized: !debug
    };


// HTTP get request
      request(options, function(error, response, body) {
        if (error) throw new Error(error);
        var result = JSON.parse(body)['gps-recs'];

        console.log(result.length);

        //create .csv file 
        buildCSV(result);

    });
});

function buildCSV(result) {


    //adding headers
    csvFile = csvFile.concat('UserNumber' + ',' + 'UserTimeTag' + ',' + 'Latitude' + ',' + 'Longitude' + ',' + 'SpeedMph' + ',' + 'Heading' + ',' + 'Status' + '\r\n');
    // loop runs result.length times
    for (var i = 0; i < result.length; i++) {
        csvFile = csvFile.concat(result[i].UserInfo.UserNumber + ',' + result[i].UserTimeTag + ',' + result[i].Latitude + ',' + result[i].Longitude + ',' + result[i].SpeedMph + ',' + result[i].Heading + ',' + result[i].Status + '\r\n');

    };
    //delete file.csv first
    console.log('before unlink: ');
    fs.unlink('file.csv', function(err){
        if (err) throw err; 
        else {
            console.log('file deleted'); 
            console.log(csvFile);
            fs.writeFile('file.csv', csvFile, function(err) {

            if (err) throw err;
            console.log('file saved');

            });
        };

    });
};
Answers:

For one thing when I run your code I get an error if no file exists in the first place. See fix below.

To be sure you are writing you could can explicitly supply the write flag to the options parameter like so:

console.log('before unlink: ');
fs.unlink('file.csv', function(err){

    // Ignore error if no file already exists
    if (err && err.code !== 'ENOENT')
        throw err;

    var options = { flag : 'w' };
    fs.writeFile('file.csv', csvFile, options, function(err) {
        if (err) throw err;
        console.log('file saved');
    });
});

Btw, fs.unlink() is not really needed since fs.writeFile() overwrites the file.