open( filePath, [mode] )

Mon, 21 Sep 2026 15:16:28 +0000

open( filePath, [mode] )

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

Caution
open() can only be called from the init context. This restriction is necessary to determine the local files needed to bundle when distributing the test across multiple nodes.

Note
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, you can:

Use open() within a SharedArray, which shares the allocated file memory between VUs.

Use open() from the k6/experimental/fs module. It provides a memory-efficient way to handle file interactions in your test script and can read files in small chunks.

Parameter	Type	Description
filePath	string	The 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.
mode	string	By default, the contents of the file are read as text, but if you specify `b`, the file will be read as binary data instead.

Returns

Type	Description
string / ArrayBuffer	The contents of the file, returned as string or ArrayBuffer (if `b` was specified as the mode).

Examples

[
  {
    "username": "user1",
    "password": "password1"
  },
  {
    "username": "user2",
    "password": "password2"
  },
  {
    "username": "user3",
    "password": "password3"
  }
]

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}`);
  sleep(3);
};

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}`);
  sleep(3);
}

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 = http.post('https://example.com/upload', data);
  sleep(3);
}

Init context on Grafana Labs

open( filePath, [mode] )

open( filePath, [mode] )

Returns

Examples