The GNU Awk User's Guide
gawk with BSD Portals
Similar to the `/inet' special files, if
is configured with the `--enable-portals' option
(see section Compiling
gawk for Unix),
files whose pathnames begin with
/p as 4.4 BSD-style portals.
When used with the `|&' operator,
gawk opens the file
for two-way communications. The operating system's portal mechanism
then manages creating the process associated with the portal and
the corresponding communications with the portal's process.