Info Catalog gawk: Two-way I/O gawk: Advanced Features gawk: Profiling

gawk: TCP/IP Networking

 
 12.4 Using 'gawk' for Network Programming
 =========================================
 
      'EMRED':
          A host is a host from coast to coast,
          and nobody talks to a host that's close,
          unless the host that isn't close
          is busy, hung, or dead.
                  -- _Mike O'Brien (aka Mr. Protocol)_
 
    In addition to being able to open a two-way pipeline to a coprocess
 on the same system (Two-way I/O), it is possible to make a
 two-way connection to another process on another system across an IP
 network connection.
 
    You can think of this as just a _very long_ two-way pipeline to a
 coprocess.  The way 'gawk' decides that you want to use TCP/IP
 networking is by recognizing special file names that begin with one of
 '/inet/', '/inet4/', or '/inet6/'.
 
    The full syntax of the special file name is
 '/NET-TYPE/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'.  The components
 are:
 
 NET-TYPE
      Specifies the kind of Internet connection to make.  Use '/inet4/'
      to force IPv4, and '/inet6/' to force IPv6.  Plain '/inet/' (which
      used to be the only option) uses the system default, most likely
      IPv4.
 
 PROTOCOL
      The protocol to use over IP. This must be either 'tcp', or 'udp',
      for a TCP or UDP IP connection, respectively.  TCP should be used
      for most applications.
 
 LOCAL-PORT
      The local TCP or UDP port number to use.  Use a port number of '0'
      when you want the system to pick a port.  This is what you should
      do when writing a TCP or UDP client.  You may also use a well-known
      service name, such as 'smtp' or 'http', in which case 'gawk'
      attempts to determine the predefined port number using the C
      'getaddrinfo()' function.
 
 REMOTE-HOST
      The IP address or fully qualified domain name of the Internet host
      to which you want to connect.
 
 REMOTE-PORT
      The TCP or UDP port number to use on the given REMOTE-HOST.  Again,
      use '0' if you don't care, or else a well-known service name.
 
      NOTE: Failure in opening a two-way socket will result in a nonfatal
      error being returned to the calling code.  The value of 'ERRNO'
      indicates the error (Auto-set).
 
    Consider the following very simple example:
 
      BEGIN {
          Service = "/inet/tcp/0/localhost/daytime"
          Service |& getline
          print $0
          close(Service)
      }
 
    This program reads the current date and time from the local system's
 TCP 'daytime' server.  It then prints the results and closes the
 connection.
 
    Because this topic is extensive, the use of 'gawk' for TCP/IP
 programming is documented separately.  See *note(General Introduction,
 gawkinet, TCP/IP Internetworking with 'gawk')Top::, for a much more
 complete introduction and discussion, as well as extensive examples.
 
      NOTE: 'gawk' can only open direct sockets.  There is currently no
      way to access services available over Secure Socket Layer (SSL);
      this includes any web service whose URL starts with 'https://'.
 

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