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From: jcurran@bbn.com (John Curran)
Newsgroups: comp.unix.wizards
Subject: Using more as an output filter via popen - pipe buffering
Keywords: pipe popen more
Message-ID: <64813@bbn.BBN.COM>
Date: 23 Jun 91 04:43:34 GMT
References: <1743@sranha.sra.co.jp> <1991Jun20.085530.24353@prl.dec.com> <1753@sranha.sra.co.jp> <1991Jun21.141740.15039@prl.dec.com>
Sender: news@bbn.com
Reply-To: jcurran@BBN.COM (John Curran)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 19

I'm looking for advice on how to utilize "more" from within a program
as an output filter.  I tried the following code segment:
 
pager = popen("{PAGER-more}","w");
for (...) {
  putc(ch++,pager)
}

This works, except that when more displays the output, it is not
possible to stop the display via the "q" command. I added a SIGPIPE
handler to longjmp and close the pipe, but that did not change the
results.  I reduced the amount of buffered data by switching to
write(fileno(pager),ch,1), but it still does not stop for files
over 8K.  Am I right in assuming that this is a result of the 
internal buffering in pipes?  Is there a method to force a
smaller pipe buffer? 
 
Thanks,
/John