Re: shell and output redirection

On 07/02/2004 04:18:26 PM, Tanel P?der wrote:

>

That is a part of pipe magic. Pipe blocks when it's full. The other program will get to it, when it executes something like read(0,&buff, SIZE); Pipes are "invisible" files allocated and mapped to the root file system. (a version of WYSE Unix used to have a possibility to define the file system used for pipes. That was extremely popular trick for benchmarking, especially when PIPEFS was pointing to a solid state disk device. A company that I worked for long, long time ago used to have a small solid state device to which PIPEFS would be pointed and on which I would put redo log files. Benchmarks against other manufacturers were great!). Unix (Linux) kernel will usually allow pipes to grow few blocks before the pipe must be read. I should go and look for that part of Linux kernel, but I'm not up to the task tonight. Hasta manana. I'll be back! (imagine me in a black leather jacket, with shades on my nose).

>
> As I saw from your trace, shell uses pipe() to create the pipe file
> descriptors for passing on data between processes.
> What if I create a pipe manually using mknod and run my two processes
> manually, does the data streaming work exactly the same way that with
> shell-generated pipe?

It probably will have the same effect, if you do it right, but why would you do it? Real programmers don't use tools provided by shell? It's called "reinventing the wheel".

-- 
Mladen Gogala
Oracle DBA



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