On Friday 05 February 2010 14:47:21 Stephen Powell wrote: > On Fri, 5 Feb 2010 12:42:47 -0500 (EST), Bob McGowan wrote: > Let me give you a > simple example of a CMS pipeline for illustrative purposes, > so that you will get some idea of what I'm talking about. >
[snip: Long, but very useful description.]
> This pipeline can be illustrated graphically as follows:
>
> +---+ +-------+ +--------+ +----------+ +---+
> |-| < |-->| NFIND |-->| LOCATE |------>| FANINANY |-->| > |-|
> +---+ +-------+ +--------+ 1 1 +----------+ +---+
> | 2 | 2
> V A
> | +--------+ |
> LOCM:-->| LOCATE |-->-FIN:
> +--------+
mkfifo "LOCM" &&
mkfifo "FIN" &&
(
"<" | "NFIND" | "LOCATE" 2> "LOCM" | "FANINANY" 2< "FIN"| ">" &
"LOCATE" < "LOCM" > "FIN" &
wait
)
People with more shell magic than me might be able to simplify that to not use
fifos, but I figured they were fair game since you get stream labels. (That's
basically all a fifo is.)
Technically speaking, that's all one command, per the Single UNIX Specifation.
It matches the shell grammar start symbol "complete_command" documented
<http://www.opengroup.org/onlinepubs/007908775/xcu/chap2.html#tag_001_010_002>.
So, basically, we have different basic building blocks (I don't know a grep
variant that acts like LOCATE, for example), but the larger structure is very
similar.
Most UNIX/Linux utilities for the command line assume all input on fd 0, all
normal output on fd 1, and end-user notifications written to fd 2. However,
there's nothing actively preventing binaries from reading from fd 2, writing
to fd 0, or expecting i/o on fds 3 through 9. (IIRC, anything greater than 9
is reserved when using the shell.)
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
b...@iguanasuicide.net ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-'
http://iguanasuicide.net/ \_/
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