Example Lambda Function to process lines of text files when uploaded to S3

CountLinesAndLetters.js

'use strict';
var AWS = require('aws-sdk');
var S3 = new AWS.S3();
var readline = require('readline');

exports.handler = function (event, context) {
    //Get S3 file bucket and name
    //Make sure to loop through event.Records, don't assume there is only 1 in production!!!
    var bucket = event.Records[0].s3.bucket.name;
    var key = event.Records[0].s3.object.key;
    
    //Create read stream from S3
    var s3ReadStream = S3.getObject({Bucket: bucket, Key: key}).createReadStream();
    //handle stream errors.
    
    //Pass the S3 read stream into the readline interface to break into lines
    var readlineStream = readline.createInterface({input: s3ReadStream, terminal: false});
    //handle stream errors

    var totalLineCount = 0;
    var totalCharCount = 0;
    readlineStream.on('line', function (line) {
        //Do whatever you need with the line
        
        //In this example we are just counting the number of lines and characters
        totalLineCount += 1;
        totalCharCount += line.length;
    });
    readlineStream.on('close', function () {
        //Do cleanup here such as persist resultant calculations.
        
        //In this example I'll just print to the log the total number of lines:        
        console.log("In s3://" + bucket + "/" + key + " there are " + totalLineCount + " lines, " + totalCharCount + " chars.");

        context.succeed();
    });
};