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open( filePath, [mode] )

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Opens a file, reading all its contents into memory for use in the script.

Use SharedArray for CSV and JSON files

open() often consumes a large amount of memory because every VU keeps a separate copy of the file in memory. To reduce the memory consumption, we strongly advise the usage of SharedArray for CSV, JSON and other files intended for script parametrization.


Function only available in "init context"

This is a function that can only be called from the init context (aka init code), code in the global context that is, outside of the main export default function { ... }.

By restricting it to the init context, we can easily determine what local files are needed to run the test and thus what we need to bundle up when distributing the test to multiple nodes in a clustered/distributed test.

See example further down on this page. For more in-depth description see Running k6.

filePathstringThe path to the file, absolute or relative, that will be read into memory. The file will only be loaded once, even when running with several VUs.
modestringBy default the contents of the file is read as text, but if you specify b the file will be read as binary data instead.


string / ArrayThe contents of the file, returned as string or array of numbers (if b was specified as the mode).
"username": "user1",
"password": "password1"
"username": "user2",
"password": "password2"
"username": "user3",
"password": "password3"
Loading JSON data with SharedArray to parameterize test
import { SharedArray } from "k6/data";
var data = new SharedArray("users", function() {
// here you can open files, and then do additional processing or generate the array with data dynamically
var f = JSON.parse(open("./users.json")).;
return f; // f must be an array[]
export default () => {
var randomUser = data[Math.floor(Math.random() * data.length)]
console.log(`${user.username}, ${user.password}`);
Loading JSON data without SharedArray
import { sleep } from 'k6';
const users = JSON.parse(open('./users.json')); // consider using SharedArray for large files
export default function () {
let user = users[__VU - 1];
console.log(`${user.username}, ${user.password}`);
Loading a binary file and POSTing it as a multipart request
import http from 'k6/http';
import { sleep } from 'k6';
let binFile = open('/path/to/file.bin', 'b');
export default function () {
var data = {
field: 'this is a standard form field',
file: http.file(binFile, 'test.bin'),
var res ='', data);