NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/unix/question/13468

Text File | 1992-11-15 | 2.1 KB | 61 lines

Newsgroups: comp.unix.questions
Path: sparky!uunet!mcsun!sunic!ericom!eos.ericsson.se!etxmesa
From: [e-mail] (Michael Salmon)
Subject: Re: problems with awk: output redirection and getline in a pipe
Message-ID: <[e-mail]>
Sender: [e-mail]
Nntp-Posting-Host: eos6c02.ericsson.se
Reply-To: [e-mail] (Michael Salmon)
Organization: Ericsson Telecom AB
References:  <[e-mail]>
Date: Mon, 16 Nov 1992 09:36:44 GMT
Lines: 47

In article <[e-mail]>,
[e-mail] writes:
|> Subject: problems in awk: output redirection and getline in a pipe
|>
|> I have written the following shell script:
|>
|> awk 'BEGIN {print "...something"}
|>            {print " ...anything for every line"}
|>     END    {printf("%2d\n", NR) >"awk.tmp" }' |
|> sort |
|> awk 'BEGIN {getline < "awk.tmp";
|>            numberoflines = $1}
|>            {print "---anything for every line"}
|>      END   {printf("%2d\n", numberoflines)} '
|>
|> In this script awk is called and an input file is processed. Output
|> is written into a pipe, temporary results are stored on a temporary file.
|>
|> The data in the pipe is transferred to UNIX sort and to a second awk program,
|> which
|> also reads the data on the temporary file by getline.
|>
|> If I start this script the first time I get 0 as result. If I start the
|> script the next times I always get a number written on the temporary file
|> in a previous run.
|>
|> What is to do now. Any help appreciated.
|> Thanks in advance.

When you start this command line you start up 3 processes
simultaneously, awk, sort and, awk. awk.tmp is not created until the
end of the first awk task. The second awk task reads from awk.tmp then
proceeds to read input from the pipe where it halts until sort is
finished. Solution: getline returns 0 if it reaches the end of its
input file so, always remove awk.tmp before this command line and then
loop waiting for getline to return something other than 0.

--

Michael Salmon

#include    <standard.disclaimer>
#include    <witty.saying>
#include    <fancy.pseudo.graphics>

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