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open( filePath, [mode] )

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 available only in init context

This function 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 the example further down on this page. For a more in-depth description, see Test lifecycle.

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 are read as text, but if you specify b, the file will be read as binary data instead.


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