partitions.js

const readline = require('readline');
const fs = require('fs');

function readLines(devs,callback) {
  var values = {};

  var rs = fs.createReadStream('./partitions');
  rs.on('error', function(e) {
    callback(e);
  });

  var rl = readline.createInterface({
    input: rs
  });

  rl.on('line', function(buffer) {
    var tokens    = buffer.toString().trim().split(/\s+/);
    var lastToken = tokens.slice(-1)[0];
    if (devs.indexOf(lastToken) != -1) {
      values[lastToken] = tokens.slice(0,2).map(function(x) { return parseInt(x); });
    }
  });
  
  rl.on('close', function() {
    callback(false,values);
  });

}
   
readLines(['sda','sda1','sda2','sda5'],function(error,result) {
  if ( error ) {
    console.log("Something went wrong: " + error.toString());
  } else {
    console.log(JSON.stringify(result));
  }
});