Write

:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::

Write from the specified FileDescriptor

namespace HH\Lib\OS;

function write(
  FileDescriptor $fd,
  string $data,
): int;

See man 2 write for details. On error, an ErrnoException will be thrown.

Parameters

• FileDescriptor $fd
• string $data

Returns

• the - number of bytes written; it is possible for this function to succeed with a partial write.