Linux in a Nutshell, 6th Edition

Coprocesses and Sockets

gawk allows you to open a two-way pipe to another process, called a coprocess. This is done with the |& operator used with getline and print or printf.

print database command |& "db_server"
"db_server" |& getline response

If the command used with |& is a filename beginning with /inet/, gawk opens a TCP/IP connection. The filename should be of the following form:

/inet/protocol/lport/hostname/rport

The parts of the filename are:

protocol

One of tcp, udp or raw, for TCP, UDP, or raw IP sockets, respectively. Note: raw is currently reserved but unsupported.

lport

The local TCP or UPD port number to use. Use 0 to let the operating system pick a port.

hostname

The name or IP address of the remote host to connect to.

rport

The port (application) on the remote host to connect to. A service name (e.g., tftp) is looked up using the C getservbyname( ) function.