Introduction to Named Pipes

Thanks for the explanation. Had been looking for something which would explain the piping structure. Am learning Unix on my netbook and this has helped me understand.

Hi Andy Vaught!
I am Phuongjolly
I have a problem:
i created two file: the first's use for read data, the second file is use for display data
readfile.sh
#!/bin/sh
a=1
b=1

exit 0

displayfile.sh
#!bin/sh
c=`expr $a + $b`
echo "Sum is $c"
exit 0

then:
bash$: /bin/bash ./readfile.sh | /bin/bash ./displayfile.sh
and have an error, but i don't know what's error
Can you help me, please! Thanks

Linux code for a client/server program using named pipes to sare some data between clients through a server

What i do not understand is the following:
When i do

mkfifo pipe pipe2; echo foo >pipe & cat pipe >pipe2 & cat < pipe2 >pipe

it sends the foo back and forth and i get a high cpu, however when I do

mkfifo pipe pipe2; echo foo >pipe & cat pipe >pipe2 & cat pipe2 >pipe

my cpu doesn't raise, so the foo isn't send back and forth. My question is:
why doesn't the latter work? does cat pipe2 >pipe differ from cat < pipe2 >pipe ?

Hey, thanks for the article. It was really helpful.

Hi,
A nice article on pipes.

I have a few questions here.

1)How to flush stdio buffers associated with the pipe.
2)What happens when there is no space on the pipe to accomodate the flushed data of the stdio buffer?

Imran

I am having a problem with using named pipes in a shell script (ksh or borne shell). As a test do something like this:

----------- cut --------
#!/bin/ksh
# This is shell script: "read_pipe"

mkfifo /tmp/event_pipe

while true
do
read EVENT </tmp/event_pipe
echo $EVENT >>/tmp/event.log
done
----------- cut -------------

Run the script via: "nohup read_pipe &".

Do something like: "cat /etc/passwd >/tmp/event_pipe". You will get some of the password file in the "/tmp/event.log", but not all of it. I tried various ways of doing the "read", but still get the same results. If I send data slowly (sleep 1 second between each line of data) it works. So what am I doing wrong? I tried a loop with "tail -f /tmp/event_pipe | while read EVENT", still the same result.
The purpose of "read_pipe" script when it does "real work", will be to process each "line" of data as it comes in. I don't know how fast the lines of data will come in, and I am afraid I will miss lines, based on the testing I did with "cat /etc/passwd". It almost appears I am overloading the "named pipe" and it is not blocking correctly. Anyone done something like this? Any ideas? Thanks.

This was quite helpful. I was wondering however if there was a way to keep a process attached to a pipe permanently. When I used the above examples, the output process worked just fine for one command and then needed to be reattached. I'll keep researching and write back if I find anything on my own.

I wanted to give C-Kermit a dynamic list of files to upload (using svn diff), and (as above) "named pipe" somehow popped into my head as maybe something I could use. I'd never sat down to figure them out, and _magic_!

Thanks a lot it helped me a lot to understand named pipes