Mkostemp

:::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 temporary file using a template filename and the specified open flags

namespace HH\Lib\OS;

function mkostemp(
  string $template,
  int $flags,
): (FileDescriptor, string);

The template must end with exactly 6 X characters; the template may be either a relative or absolute path, however the parent directory must already exist.

This function takes the same flags as OS\open(); like that function, O_CLOEXEC is implied.

The temporary file:

• will be a new file (i.e. O_CREAT | O_EXCL)
• be owned by the current user
• be created with mode 0600

Parameters

• string $template
• int $flags

Returns

• a - FileDescriptor and the actual path.