Very Computer

We have a shell script which does something like this:

    $pipe = /tmp/xxx
    mkfifo $pipe
    log_reader_script < $pipe &

    main_program | tee -a $pipe &

I was wondering, if I do the following:

    main_program | tee -a | log_reader_script

What are the avantages, disadvantages of each approach?

Thanks for your kind help.

Regards,
Ashish

The second generates a syntax error.

the '-a' option for tee(1) requires a parameter (interpreted as a file name)
to follow it.  There is no such parameter before the '|' that terminates the
current command and begins the next command.

So, if we do :

    main_program | tee -a /dev/tty | log_reader_script &

Are there any advantages/disadvantages over :

    $pipe = /tmp/xxx
    mkfifo $pipe
    log_reader_script < $pipe &

    main_program | tee -a $pipe &

Another question related to pipes: Can two processes read from the same
named pipe ?
I experimented as follows.
First, I had given the command: log_reader_script < $pipe &
After some time, I gave the command: log_reader_script1 < $pipe &
It seemed to me that after giving the second command, log_reader_script
stopped reading from $pipe and log_reader_script1 started reading from
$pipe.

Is this expected, correct behaviour.

Thanks and regards,
Ashish

Now consider what happens if you re-direct the output of that script.

Quote:>Another question related to pipes: Can two processes read from the same
>named pipe ?
>I experimented as follows.
>First, I had given the command: log_reader_script < $pipe &
>After some time, I gave the command: log_reader_script1 < $pipe &
>It seemed to me that after giving the second command, log_reader_script
>stopped reading from $pipe and log_reader_script1 started reading from
>$pipe.

>Is this expected, correct behaviour.

What happens if you have two processes trying to read from a device (say a
tty) simultaneously?

Any given input goes to _one_ of the processes.

But "which one"?

GOOD question!

See "nasal pigs" for an authoritative discussion of how these kind of
situations work.