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This function is available as OS\isatty() in Facebook's www repository.

Test if a file descriptor refers to a terminal

namespace HH\Lib\OS;

function isatty(
  FileDescriptor $fd,
): bool;

If the native call fails with ENOTTY (for example, on MacOS), this function will return false.

If the native call fails with any other error (for example, EBADF), this function will throw.


  • FileDescriptor $fd


  • bool