(gawkinet.info)Gawk Special Files
`gawk' Networking Mechanisms ============================ The `|&' operator introduced in `gawk' 3.1 for use in communicating with a "co-process" is described in Note: Two-way Communications With Another Process. 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 "co-process" is started that matches the special files we are about to describe, `gawk' creates the appropriate network connection, and then two-way I/O proceeds as usual. At the C, C++ (and basic 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 them mandatory, none of them optional: /inet/PROTOCOL/LOCALPORT/HOSTNAME/REMOTEPORT The `/inet/' field is, of course, constant when accessing the network. The LOCALPORT and REMOTEPORT fields do not have a meaning when used with `/inet/raw' because "ports" only apply to TCP and UDP. So, when using `/inet/raw', the port fields always have to be `0'.
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