Pipe

:::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. :::

Create a pair of connected file descriptors

namespace HH\Lib\OS;

function pipe(): (FileDescriptor, FileDescriptor);

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

O_CLOEXEC is implicitly set for consistent behavior between standalone CLI mode and server modes. Use OS\fcntl() to remove if needed.

Returns

• Two - FileDescriptors; the first is read-only, and the second is write-only. Data written to the second can be read from the first.