recvfd program
recvfd socket {fd|$VAR} [...] : command arg ...
recvfd receives one or more file descriptors over a
Unix-domain socket (such as those opened with
s6-ipcclient/s6-ipcserver
or ucspi-unix). Another
process that has a descriptor for the other end of the socket can send the
descriptors using the fd_xfer_send() library function. The
received descriptors will not necessarily have the same numeric values, but
will refer to the same open file handles, as if by dup(). After
receiving the descriptors, recvfd moves them to the descriptor
numbers specified on the command line with dup2(), or sets the
given environment variables (prefixed with "$") to
indicate what descriptor numbers were received. Finally, recvfd
execs the given command. A colon separates the file descriptors
and environment variable names from the command.
This is useful, for example, in network clients that want to use UCSPI client programs to establish connections, but which can't have all connections opened at startup.