difference between normal file and named pipe file

HI,
        will anyone let me know the differences between the normal unix
file and named pipe file?

Regards

In article < XXXX@XXXXX.COM >,




A normal file is a bunch of data sitting on disk.

A named pipe is a way for two processes to connect to each other and 
send data directly.

-- 
Barry Margolin,  XXXX@XXXXX.COM 
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
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> In article < XXXX@XXXXX.COM >,



A file keeps all the data until deleted/overwritten while iiuc a named 
pipe dumps the data after it is read. So a temp file could keep growing 
and fill a file system, but a named pipe is less likey to for, say, long 
running processes.

   3ch

I'm not sure I understand this - a write to a named pipe will block if
there is no corresponding process reading from the pipe, usually
blocking the whole process until there's a reader.  This in itself is
can be quite a useful shell hack - it allows to send a signal between
two processes, potentially owned by different users, without root
permissions being needed.

-- 
Andrew Smallshaw
 XXXX@XXXXX.COM 

I'm not sure what part you don't understand (perhaps I've said something 
wrong) but:
An open for writing to a named pipe will block if there is no process with 
the file open for reading (and vice versa). But it dosen't have to be 
actively reading for the writer to write, so the file can still grow. I 
think there is also some smaller limit that for a normal file. But the 
blocking scheme is also an important difference.

   3ch

In article < XXXX@XXXXX.COM >,







What file?  There's no file associated with a named pipe, it's just a 
kernel connection between the two processes.


There's typically a buffer of about 4KB in the kernel.  So if the writer 
writes faster than the reader reads, the writer will block when it gets 
4K ahead of the reader.

-- 
Barry Margolin,  XXXX@XXXXX.COM 
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

Well. Thanks for your answers.  The differences what you have given are
functional. Can anyone tell me the implementation level differencs
between normal unix files and named pipe files?

Regards

A -named- pipe? Per Maurice Bach in The Design of the Unix operating 
system: "A named pipe is a file whose semantics are the same as those of 
an unnamed pipe, except it has a directory entry and is accessed by a path 
name." Also he says the size limit is set by the use of only direct blocks 
of the inode but he is talking about System V

Under FreeBSD (and similar under Fedora core 3):
%ls
%
%mkfifo joe
%ls
joe
%echo "1234567890" > joe

hangs until I do
%cat joe
1234567890
%
in another terminal.
and
%ls -i
147374 joe
show it has an inode

Perhaps in modern unices the name is stored in the file system but data 
in buffers, but it has a directory entry and and inode. That is what I 
meant by calling it a file anyway.

This has encouraged me read up on named pipes though :-)

   3ch

In article < XXXX@XXXXX.COM >,






If everything that has a directory entry is a file, then yes it's a 
file, and so is a tty device, tape drive, etc.  I was using the term in 
the more traditional sense to mean a collection of non-volatile data on 
some storage medium.

-- 
Barry Margolin,  XXXX@XXXXX.COM 
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

More traditional outside of unix, but it is the standard unix terminology. 
"Everything is a file" and all that.

   3ch

In article < XXXX@XXXXX.COM >,






Yeah, I never was a big fan of Unix's term "special file".

-- 
Barry Margolin,  XXXX@XXXXX.COM 
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***