GAWK: Effective AWK Programming

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172 GAWK: Effective AWK Programmingprint ... |& command...# start two-way pipeUsing ptys avoids the buffer deadlock issues described earlier, at some loss in performance.If your system does not have ptys, or if all the system’s ptys are in use, gawk automaticallyfalls back to using regular pipes.10.3 Using gawk for Network ProgrammingEMISTERED: A host is a host from coast to coast,and no-one can talk to host that’s close,unless the host that isn’t closeis busy hung or dead.In addition to being able to open a two-way pipeline to a coprocess on the same system(see Section 10.2 [Two-Way Communications with Another Process], page 170), it is possibleto make a two-way connection to another process on another system across an IP networkingconnection.You can think of this as just a very long two-way pipeline to a coprocess. The way gawkdecides that you want to use TCP/IP networking is by recognizing special file names thatbegin with ‘/inet/’.The full syntax of the special file name is ‘/inet/protocol/local-port/remotehost/remote-port’.The components are:protocollocal-portThe protocol to use over IP. This must be either ‘tcp’, ‘udp’, or ‘raw’, for aTCP, UDP, or raw IP connection, respectively. The use of TCP is recommendedfor most applications.Caution: The use of raw sockets is not currently supported in version 3.1 ofgawk.The local TCP or UDP port number to use. Use a port number of ‘0’ whenyou want the system to pick a port. This is what you should do when writinga 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 portnumber using the C getservbyname function.remote-hostThe IP address or fully-qualified domain name of the Internet host to whichyou want to connect.remote-portThe 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 non-fatal error beingreturned to the calling function.Consider the following very simple example:BEGIN {Service = "/inet/tcp/0/localhost/daytime"Service |& getline
Chapter 10: Advanced Features of gawk 173}print $0close(Service)This program reads the current date and time from the local system’s TCP ‘daytime’server. It then prints the results and closes the connection.Because this topic is extensive, the use of gawk for TCP/IP programming is documentedseparately. See TCP/IP Internetworking with gawk, which comes as part of the gawkdistribution, for a much more complete introduction and discussion, as well as extensiveexamples.10.4 Using gawk with BSD PortalsSimilar to the ‘/inet’ special files, if gawk is configured with the ‘--enable-portals’option (see Section B.2.1 [Compiling gawk for Unix], page 268), then gawk treats files whosepathnames begin with /p as 4.4 BSD-style portals.When used with the ‘|&’ operator, gawk opens the file for two-way communications. Theoperating system’s portal mechanism then manages creating the process associated with theportal and the corresponding communications with the portal’s process.10.5 Profiling Your awk ProgramsBeginning with version 3.1 of gawk, you may produce execution traces of your awk programs.This is done with a specially compiled version of gawk, called pgawk (“profiling gawk”).pgawk is identical in every way to gawk, except that when it has finished running, itcreates a profile of your program in a file named ‘awkprof.out’. Because it is profiling, italso executes up to 45% slower than gawk normally does.As shown in the following example, the ‘--profile’ option can be used to change thename of the file where pgawk will write the profile:$ pgawk --profile=myprog.prof -f myprog.awk data1 data2In the above example, pgawk places the profile in ‘myprog.prof’ instead of in ‘awkprof.out’.Regular gawk also accepts this option. When called with just ‘--profile’, gawk “prettyprints” the program into ‘awkprof.out’, without any execution counts. You may supply anoption to ‘--profile’ to change the file name. Here is a sample session showing a simpleawk program, its input data, and the results from running pgawk. First, the awk program:BEGIN { print "First BEGIN rule" }END { print "First END rule" }/foo/ {print "matched /foo/, gosh"for (i = 1; i
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