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Diffstat (limited to 'doc/gawkinet.info')
| -rw-r--r-- | doc/gawkinet.info | 124 |
1 files changed, 71 insertions, 53 deletions
diff --git a/doc/gawkinet.info b/doc/gawkinet.info index 71724910..16313b60 100644 --- a/doc/gawkinet.info +++ b/doc/gawkinet.info @@ -700,22 +700,26 @@ File: gawkinet.info, Node: TCP Connecting, Next: Troubleshooting, Prev: Gawk Let's observe a network connection at work. Type in the following program and watch the output. Within a second, it connects via TCP -('/inet/tcp') to the machine it is running on ('localhost') and asks the -service 'daytime' on the machine what time it is: +('/inet/tcp') to a remote server and asks the service 'daytime' on the +machine what time it is: BEGIN { - "/inet/tcp/0/localhost/daytime" |& getline + daytime_server = "time-a-g.nist.gov" + daytime_connection = "/inet/tcp/0/" daytime_server "/daytime" + daytime_connection |& getline print $0 - close("/inet/tcp/0/localhost/daytime") + daytime_connection |& getline + print $0 + close(daytime_connection) } - Even experienced 'awk' users will find the second line strange in two -respects: + Even experienced 'awk' users will find the fourth and sixth line +strange in two respects: - * A special file is used as a shell command that pipes its output - into 'getline'. One would rather expect to see the special file - being read like any other file ('getline < - "/inet/tcp/0/localhost/daytime"'). + * A string containg the name of a special file is used as a shell + command that pipes its output into 'getline'. One would rather + expect to see the special file being read like any other file + ('getline < "/inet/tcp/0/time-a-g.nist.gov/daytime"'). * The operator '|&' has not been part of any 'awk' implementation (until now). It is actually the only extension of the 'awk' @@ -738,12 +742,26 @@ operator except for two additions: written to, just like a full-duplex network connection. In the earlier example, the '|&' operator tells 'getline' to read a -line from the special file '/inet/tcp/0/localhost/daytime'. We could -also have printed a line into the special file. But instead we just -read a line with the time, printed it, and closed the connection. -(While we could just let 'gawk' close the connection by finishing the -program, in this Info file we are pedantic and always explicitly close -the connections.) +line from the special file '/inet/tcp/0/time-a-g.nist.gov/daytime'. We +could also have printed a line into the special file. But instead we +just consumed an empty leading line, printed it, then read a line with +the time, printed that, and closed the connection. (While we could just +let 'gawk' close the connection by finishing the program, in this Info +file we are pedantic and always explicitly close the connections.) + + Network services like 'daytime' are not really useful because there +are so many better ways to print the current time. In the early days of +TCP networking, such a service may have looked like a good idea for +testing purposes. Later, simple TCP services like these have been used +to teach TCP/IP networking and therefore you can still find much +educational material of good quality on the Internet about such outdated +services. The list of servers (https://tf.nist.gov/tf-cgi/servers.cgi) +that still support the legacy service daytime +(https://en.wikipedia.org/wiki/Daytime_Protocol) can be found at +Wikipedia. We hesitated to use this service in this manual because it +is hard to find servers that still support services like 'daytime' +openly to the Internet. Later on we will see that some of these +nostalgic protocols have turned into security risks. File: gawkinet.info, Node: Troubleshooting, Next: Interacting, Prev: TCP Connecting, Up: Using Networking @@ -4179,7 +4197,7 @@ Index * /inet/ files (gawk): Gawk Special Files. (line 34) * /inet/tcp special files (gawk): File /inet/tcp. (line 6) * /inet/udp special files (gawk): File /inet/udp. (line 6) -* | (vertical bar), |& operator (I/O): TCP Connecting. (line 25) +* | (vertical bar), |& operator (I/O): TCP Connecting. (line 29) * advanced features, network connections: Troubleshooting. (line 6) * agent: Challenges. (line 75) * agent <1>: MOBAGWHO. (line 6) @@ -4283,7 +4301,7 @@ Index * Perl: Using Networking. (line 14) * Perl, gawk networking and: Using Networking. (line 24) * Perlis, Alan: MAZE. (line 6) -* pipes, networking and: TCP Connecting. (line 30) +* pipes, networking and: TCP Connecting. (line 34) * PNG image format: Web page. (line 45) * PNG image format <1>: STATIST. (line 6) * POP (Post Office Protocol): Email. (line 6) @@ -4342,7 +4360,7 @@ Index * UDP (User Datagram Protocol), TCP and: Interacting. (line 48) * Unix, network ports and: Setting Up. (line 37) * URLCHK program: URLCHK. (line 6) -* vertical bar (|), |& operator (I/O): TCP Connecting. (line 25) +* vertical bar (|), |& operator (I/O): TCP Connecting. (line 29) * VRML: MAZE. (line 6) * web pages: Web page. (line 6) * web pages, images in: Interacting Service. (line 190) @@ -4381,40 +4399,40 @@ Node: File /inet/tcp26947 Node: File /inet/udp27933 Ref: File /inet/udp-Footnote-129645 Node: TCP Connecting29899 -Node: Troubleshooting32245 -Ref: Troubleshooting-Footnote-135073 -Node: Interacting36030 -Node: Setting Up38754 -Node: Email42726 -Node: Web page45109 -Ref: Web page-Footnote-147929 -Ref: Web page-Footnote-248127 -Node: Primitive Service48621 -Node: Interacting Service51355 -Ref: Interacting Service-Footnote-160510 -Node: CGI Lib60542 -Node: Simple Server67542 -Ref: Simple Server-Footnote-175344 -Node: Caveats75445 -Node: Challenges76588 -Ref: Challenges-Footnote-185330 -Node: Some Applications and Techniques85431 -Node: PANIC87892 -Node: GETURL89618 -Node: REMCONF92251 -Node: URLCHK97747 -Node: WEBGRAB101591 -Node: STATIST106055 -Ref: STATIST-Footnote-1119203 -Node: MAZE119646 -Node: MOBAGWHO125871 -Ref: MOBAGWHO-Footnote-1139773 -Node: STOXPRED139841 -Node: PROTBASE154133 -Ref: PROTBASE-Footnote-1167300 -Node: Links167415 -Node: GNU Free Documentation License170306 -Node: Index195426 +Node: Troubleshooting33332 +Ref: Troubleshooting-Footnote-136160 +Node: Interacting37117 +Node: Setting Up39841 +Node: Email43813 +Node: Web page46196 +Ref: Web page-Footnote-149016 +Ref: Web page-Footnote-249214 +Node: Primitive Service49708 +Node: Interacting Service52442 +Ref: Interacting Service-Footnote-161597 +Node: CGI Lib61629 +Node: Simple Server68629 +Ref: Simple Server-Footnote-176431 +Node: Caveats76532 +Node: Challenges77675 +Ref: Challenges-Footnote-186417 +Node: Some Applications and Techniques86518 +Node: PANIC88979 +Node: GETURL90705 +Node: REMCONF93338 +Node: URLCHK98834 +Node: WEBGRAB102678 +Node: STATIST107142 +Ref: STATIST-Footnote-1120290 +Node: MAZE120733 +Node: MOBAGWHO126958 +Ref: MOBAGWHO-Footnote-1140860 +Node: STOXPRED140928 +Node: PROTBASE155220 +Ref: PROTBASE-Footnote-1168387 +Node: Links168502 +Node: GNU Free Documentation License171393 +Node: Index196513 End Tag Table |