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Q: Unix test question/answer dispute ( Answered 5 out of 5 stars,   3 Comments )
Subject: Unix test question/answer dispute
Category: Computers > Operating Systems
Asked by: hellznrg-ga
List Price: $2.00
Posted: 11 Nov 2004 00:20 PST
Expires: 11 Dec 2004 00:20 PST
Question ID: 427457
in a C++/Unix test, a question asked was "State the difference between
pipeline and redirection". I answered it as follows:

Pipeline directs data flow to/from programs.
Redirection directs data flow from programs to file or from file to program.

my answer was marked wrong and i got zero out of two points. however i
think i deserve full marks for my answer.... what do u think?
Subject: Re: Unix test question/answer dispute
Answered By: hammer-ga on 11 Nov 2004 05:04 PST
Rated:5 out of 5 stars
Your answer shows that you have a correct basic understanding of the
concept. My partner has been a UNIX programmer for 22 years, and he
also says it looks right to him.

You may have simply failed to use a particular term they were looking
for, or they may have wanted a more thorough (longer) explanation. For
example, you don't discuss the limitations. You also don't discuss the
specific differences in behavior.

Additional resources
Pipes, Lists & Redirection

man pipes

man pages for different shells usually discuss redirection

Search Strategy
Google Search: pipe redirect

- Hammer
hellznrg-ga rated this answer:5 out of 5 stars
thanks... your answer was great... i don't really have a great deal of
experience in unix, but while i was using pipelining and redirection
in unix, the understanding of the basic difference just "came" to me.

if u enter this command "echo x|more", the shell will run the echo
command and pipeline the output to the _program_ called "more"

however, if u enter this command "echo x>more", the shell will run the
echo command and redirect the output to a _file_ called "more"

Subject: Re: Unix test question/answer dispute
From: mathtalk-ga on 11 Nov 2004 05:41 PST
I agree with hammer-ga that your answer was basically correct.  This
is a difficult question to grade in my opinion, because of the variety
of ways to distinguish these closely related Unix shell concepts.

A completely superficial approach might have been to say:  Pipelining
uses the pipe (|) symbol.   Redirection uses inequality symbols (<,>).

A more significant observation, which your answer verges on without
explicitly bringing out, is that pipelining can involve a succession
of multiple programs (filters) written to take advantage of
redirection.  In this sense pipelining relies on the more elementary
redirection feature.

regards, mathtalk-ga
Subject: Re: Unix test question/answer dispute
From: crythias-ga on 11 Nov 2004 06:52 PST
Perhaps this: a Pipeline takes output from the program to the left of
the | and uses that output as the input for the program to the right
of the |.

A redirect is a bit more complicated. It can override stdin (<),
stdout (>), and stderr (2>).  It has the ability to use a file as the
source for input and can store the output in a file. Redirect also
allows the ability to append to an existing file (>>).

Respectfully, although the answer demonstrates the most basic grasp of
the differences, it doesn't address understanding of usage which may
be more of what the grader is intending to check.
Subject: Re: Unix test question/answer dispute
From: hellznrg-ga on 12 Nov 2004 16:05 PST
hey u guys... thanks a million for your helpful answers...! too bad i
can't rate mathtalk and crythias... for i would have given u both 5
stars too...

as to your queries, the professor in fact did say that he would have
preferred a memorized definition... :( i'm good in this subject,
possibly one of the best students in the class, but i fear i may fail
this subject... that sucks big time

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