nodejs: Detecting multiple occurrence of same string in file-CodePudding

In nodejs is it possible to detect multiple occurrences of the same string in a txt file?

My current code is as below

const fs = require('fs');
var file_path = 'file.txt';
fs.readFile(file_path, "UTF-8", (error, data) => {
    if (error) throw error;
    else {
        if (data.includes('Test Value')) {
            console.log(data.indexOf('Test Value'))
        }
        fs.close(file, (err) => {
            if (err)
                console.error('Failed to close file', err);
            else {
                console.log("\n> File Closed successfully");
            }
        });
    }
});

In file.txt, I have below contents

Value1
Value2
Test Value
Value3
Test Value
Value4

when I run the above code, I could only detect first occurrence of 'Test Value' whereas I need to detect all occurrences of 'Test Value' in file.txt, please help

CodePudding user response：

indexOf has two parameters. You can use store the last position and continue the next search at the next position:

const fs = require('fs');
var file_path = 'file.txt';
fs.readFile(file_path, "UTF-8", (error, data) => {
    if (error) throw error;
    else {
        
        for (let pos = data.indexOf('Test Value'); pos > -1; pos = data.indexOf('Test Value', pos   1)) {
            console.log(pos);
        }
        fs.close(file, (err) => {
            if (err)
                console.error('Failed to close file', err);
            else {
                console.log("\n> File Closed successfully");
            }
        });
    }
});

Example:

const data = `Value1
Value2
Test Value
Value3
Test Value
Value4`;

for (let pos = data.indexOf('Test Value'); pos > -1; pos = data.indexOf('Test Value', pos   1)) {
    console.log(pos);
}

CodePudding user response：

You can use a regexp global search (multiple matches) with the RegExp .exec() method.

A global search using the String .match() method returns just the matches without the index. However the RegExp .exec() method returns the index.

let match;
let search = /Test Value/g; // <-- the 'g' flag is important!

// If you need to construct the regexp dynamically
// do = new RegExp('Test Value', 'g')

while (match = search.exec(data)) {
    console.log(match.index);
}

CodePudding user response：

I used an array to store occurrences (line number) of a particular string in a file.

var linepos = [];
fs.readFile(file_name, "UTF-8", (error, data) => {
    if (error) throw error;
    else {
        let pos = 0;
        data.split(/\r?\n/).forEach(line => {
            if (line == 'Test Value') {
                //console.log(pos)
                linepos.push(pos);
            }
            pos = pos   1
        });
    }
});

and then used this array to perform other operations such as append etc with foreach

linepos.forEach((item) => {
    //operations body
});

CodePudding user response：

Yes. Loop through the data array and check each data element.

const fs = require('fs');
var file_path = 'file.txt';
fs.readFile(file_path, "UTF-8", (error, data) => {
    if (error) throw error;
    else {
        data.split('\n').forEach(line => {
            if (line === 'Test Value') {
                console.log(data.indexOf(line))
            }
        })
        fs.close(file, (err) => {
            if (err)
                console.error('Failed to close file', err);
            else {
                console.log("\n> File Closed successfully");
            }
        });
    }
});