gawk’s Networking MechanismsThe ‘|&’ operator for use in
communicating with a coprocess is described in
Two-way Communications With Another Process in GAWK: Effective AWK Programming.
It shows how to do two-way I/O to a
separate process, sending it data with print or printf and
reading data with getline. If you haven’t read it already, you should
detour there to do so.
gawk transparently extends the two-way I/O mechanism to simple networking through
the use of special file names. When a “coprocess” that matches
the special files we are about to describe
is started, gawk creates the appropriate network
connection, and then two-way I/O proceeds as usual.
At the C, C++, and Perl level, networking is accomplished
via sockets, an Application Programming Interface (API) originally
developed at the University of California at Berkeley that is now used
almost universally for TCP/IP networking.
Socket level programming, while fairly straightforward, requires paying
attention to a number of details, as well as using binary data. It is not
well-suited for use from a high-level language like awk.
The special files provided in gawk hide the details from
the programmer, making things much simpler and easier to use.
The special file name for network access is made up of several fields, all of which are mandatory:
/net-type/protocol/localport/hostname/remoteport
The net-type field lets you specify IPv4 versus IPv6, or lets you allow the system to choose.