Re: [PLUG] Linux FIFOs

[Martin DiViaio <scatterbrained@usermail.com>]

On the 11th day of April in the year 2003 you wrote:

> Date: 11 Apr 2003 01:24:12 -0400
> From: Michael F. Robbins <mike@gamerack.com>
> To: Philadelphia Linux User Group <plug@lists.phillylinux.org>
> X-Spam-Status: No, hits=-0.5 required=5.0
> 	tests=IN_REP_TO,QUOTED_EMAIL_TEXT,REFERENCES,SPAM_PHRASE_05_08
> 	version=2.44
> Subject: Re: [PLUG] Linux FIFOs
> 
> On Thu, 2003-04-10 at 22:47, Martin DiViaio wrote:
> > I have a signature rotation script that creates a FIFO to output to. I 
> > then just point pine to the FIFO filename. This doesn't seem to want to 
> > work as it use to.
> 
> I'm sure you've asked yourself already, but what changed?  New version
> of pine/your scripting language/kernel?
> 

All three, actually. The original script ran under Pine 3.96 to 4.10, Perl 
5.005, and kernels 2.0.36 thru 2.2.19. I haven't used the script since.

I'm now running Pine 4.44, Perl 5.6.1 and kernel 2.4.21-pre4.

> > and it would just start dumping sigs out until I CTRL-C'd the tail. It
> > doesn't do this anymore. It reads the FIFO the first time then just hangs.  
> > The write program makes several more dumps to the FIFO then also hangs.  
> > If I kill the tail at that point, the write program dies with a broken
> > pipe error.
> 
> "man 4 fifo" might provide some insight.  Also, make sure that you
> aren't being thwarted by FIFO buffering.  I imagine that this will be
> specific to the language that you are using.  (When I did some FIFO work
> in C++ I had to be careful to keep flushing the stream after every
> write.)

I've read it and the information in Programming Perl. I think I'm doing 
this correctly - although I could be missing something stupid.

> 
> To make sure the kernel FIFO behavior is sane, try it manually.  Make a
> FIFO file, cat > thefifo on one virtual console, and  tail -f thefifo
> (or run pine) on another VC.

Ok...

-- console 1
Belgarath:martin:~:1025 $ mkfifo fifo
Belgarath:martin:~:1026 $ for i in 1 2 3 4 5 6 7 8 9 10; do echo -n "$i "; cat textfile > fifo; sleep 1 ; done
1 

-- console 2
Belgarath:martin:~:1002 $ tail -f fifo
this is the start of a text file

this is some random text

this is the end of a text file

-- console 1
Belgarath:martin:~:1025 $ mkfifo fifo
Belgarath:martin:~:1026 $ for i in 1 2 3 4 5 6 7 8 9 10; do echo -n "$i ";
 cat textfile > fifo; sleep 1 ; done
1 2 3 4 5 6 7 8 9 10 Belgarath:martin:~:1027 $ 

Console 2 will hang until I kill the tail.

Thanks for your help.

Here is the actual script. (Which acts the same way as above.)

#!/usr/bin/perl -wT --
use strict;
delete @ENV{qw/IFS CDPATH ENV BASH_ENV/};
$ENV{'PATH'}=''; $|++;

my $quote_div="%\n";
my $credit_div="-----\n";
my $quote_file='/home/martin/docs/quotes';
my $sig_file='/home/martin/.signature/usermail';
my $output_stack='/home/martin/.signature/random_quote';

use Fcntl;
use POSIX;

my $unchanged_sig='';
open(IN1,"<${sig_file}");
while(<IN1>) { $unchanged_sig.=$_; }
close IN1;

my $temp_del=$/;
$/=$quote_div;
open(IN1,"<${quote_file}") || die "Can not open quote file for reading: ${!}\n";
my $quote_count=0;
while(<IN1>) { $quote_count++; }
close IN1;
$/=$temp_del;

unlink $output_stack;
POSIX::mkfifo($output_stack,0600) || die "cannot mknod output stack: ${!}\n";

my($quote,$credit,$quote_number)=('','',0);
while(1) {
 $quote_number=int(rand($quote_count));
 print "${quote_number} ";
 $quote=''; $credit='';
 $temp_del=$/;
 $/=$quote_div;
 open(IN1,"<${quote_file}") || die "cannot open quote file for reading (again): ${!}\n";
 my $ln='';
 for(my $i=1;$i<=$quote_number;$i++) { $ln=<IN1>; }
 close IN1;
 $/=$temp_del;
 $ln=~s/$quote_div//sgi;
 ($quote,$credit)=split $credit_div,$ln;
 $credit='' unless $credit;
 sysopen(OUT1,$output_stack,O_WRONLY);
 write OUT1;
 close OUT1;
 select(undef,undef,undef,0.2);
}

format OUT1 =
@*
$unchanged_sig
@*
$quote

^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<~~
$credit
.

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