/sys$common/syshlp/helplib.hlb CC, Run-time functions, isapipe  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Returns 1 if the specified file descriptor is associated with a
  pipe, and 0 if it is not.

  Syntax:

       #include <unixio.h>

       int isapipe(int file_descriptor);