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Groups > comp.os.linux.networking > #2068
| From | "Chris F.A. Johnson" <cfajohnson@gmail.com> |
|---|---|
| Newsgroups | comp.os.linux.networking, comp.os.linux.misc |
| Subject | Re: Mental-model of multiprocessing? |
| Date | 2013-03-29 18:55 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <9oih2a-s2t.ln1@cfa.johnson> (permalink) |
| References | <rovg2ax8ap.ln2@news.roaima.co.uk> <kj500f$qll$1@dont-email.me> |
Cross-posted to 2 groups.
On 2013-03-29, Avoid9Pdf@gmail.com wrote:
...
> Has `echo` got an 'input' too?
Yes, but it doesn 't read it.
> What's the definition of 'attached to'?
'sends output to' or 'reads input from'
> Has `pwd` also got a pipeable input?
I*t's not 'pipeable', because it doesn 't read it.
>> Using these simplified rules you can see that this next command line
>> takes the stdout from echo and writes to the stdin of cat. Cat is defined
>> to send its inputs to stdout, and that isn't redirected anywhere so it
>> appears on your terminal.
>>
>> echo "hello, world" | cat
>> Easy really.
>>
> Which you would never write [nor echo "hello" | cat | cat | cat ]
But you could, and it would work.
> But the original code used THIS syntax, and that may be the key
> to understanding the code. So then:
> cat>/tmp/mesgFile
> (
> read line 0<&3 ; echo "$line">$log
> case "$line" in 2*) ;; *) echo "QUIT" 1>&3 ; exit 0 ;; esac
> echo "HELO $local_name" 1>&3
> ) 3<>/dev/tcp/$smtp_server/25
>
> would mean
> "stdin [since none is provided]" writeTo /tmp/mesgFile
> the sequential output of the bracketed-statements
> [which also write to there OWN destinations]
> .... ??
>
> Does: 3<>/dev/tcp/$smtp_server/25
> mean: let fd3 have input AND output to that-device?
Yes. Read the man page:
Opening File Descriptors for Reading and Writing
The redirection operator
[n]<>word
causes the file whose name is the expansion of word to be
opened for both reading and writing on file descriptor n, or on
file descriptor 0 if n is not specified. If the file does not
exist, it is created.
> *THAT* is the 'fraud'(:-;) !!
> Only AFTER it's been used is it defined.
The shell parses the line and sets up redirection before executing
the command.
...
> It would be good if the *nix docos put UP FRONT that
> 'it's not parsed sequentially left-to-right'; like computers
> work or mathematical theorems are proved.
It *is* explained in the man page.
> It works like poetry: you must get the whole picture
> before interpreting.
Yes, that's what the shell does.
--
Chris F.A. Johnson, <http://cfajohnson.com>
Author:
Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress)
Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
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Mental-model of multiprocessing? Avoid9Pdf@gmail.com - 2013-03-27 11:13 +0000
Re: Mental-model of multiprocessing? Joe Beanfish <joebeanfish@nospam.duh> - 2013-03-27 14:02 +0000
Re: Mental-model of multiprocessing? Richard Kettlewell <rjk@greenend.org.uk> - 2013-03-27 14:13 +0000
Re: Mental-model of multiprocessing? The Natural Philosopher <tnp@invalid.invalid> - 2013-03-27 14:35 +0000
Re: Mental-model of multiprocessing? Chris Davies <chris-usenet@roaima.co.uk> - 2013-03-27 15:30 +0000
Re: Mental-model of multiprocessing? The Natural Philosopher <tnp@invalid.invalid> - 2013-03-27 18:57 +0000
Re: Mental-model of multiprocessing? Richard Kettlewell <rjk@greenend.org.uk> - 2013-03-27 21:15 +0000
Re: Mental-model of multiprocessing? The Natural Philosopher <tnp@invalid.invalid> - 2013-03-27 21:36 +0000
Re: Mental-model of multiprocessing? Aragorn <stryder@telenet.be.invalid> - 2013-03-28 06:56 +0100
Re: Mental-model of multiprocessing? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2013-03-27 21:47 +0000
Re: Mental-model of multiprocessing? Avoid9Pdf@gmail.com - 2013-03-29 14:28 +0000
Re: Mental-model of multiprocessing? The Natural Philosopher <tnp@invalid.invalid> - 2013-03-29 15:32 +0000
Re: Mental-model of multiprocessing? J G Miller <miller@yoyo.ORG> - 2013-03-29 22:36 +0000
Re: Mental-model of multiprocessing? Chris Davies <chris-usenet@roaima.co.uk> - 2013-03-29 17:31 +0000
Re: Mental-model of multiprocessing? Avoid9Pdf@gmail.com - 2013-03-29 21:10 +0000
Re: Mental-model of multiprocessing? "Chris F.A. Johnson" <cfajohnson@gmail.com> - 2013-03-29 18:55 -0400
Re: Mental-model of multiprocessing? Unknown <dog@gmail.com> - 2013-03-30 06:01 +0000
Re: Mental-model of multiprocessing? Chris Davies <chris-usenet@roaima.co.uk> - 2013-03-30 21:28 +0000
Re: Mental-model of multiprocessing? Joe Beanfish <joebeanfish@nospam.duh> - 2013-04-01 15:32 +0000
Re: Mental-model of multiprocessing? Unknown <dog@gmail.com> - 2013-04-03 08:00 +0000
Re: Mental-model of multiprocessing? Joe Beanfish <joebeanfish@nospam.duh> - 2013-04-08 14:47 +0000
Re: Mental-model of multiprocessing? Unknown <dog@gmail.com> - 2013-04-03 08:02 +0000
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