Redirection

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2 total messages Started by Thomas Kwong Thu, 27 Dec 1990 00:31

#359

Author: Thomas Kwong
Date: Thu, 27 Dec 1990 00:31

25 lines
884 bytes

In the final exam ( Unix and C ) that I just take, one UNIX
problem is like this:

%cat myfile
word1 word2 word3
word4 word5
word6
%wc myfile
     3     6    36   myfile

%wc myfile > myfile
%cat myfile
     0     0     0   myfile

How come MYFILE becomes that?

I think it should be like:
     3     6    36   myfile
because output of wc myfile is redirected to myfile.

Can anybody tell me why?

Thomas Kwong.

------------------------------ 6600tom@ucsbuxa.ucsb.edu

Re: Redirection

#362

Author: Steven Freed CIRT
Date: Thu, 27 Dec 1990 16:44

19 lines
905 bytes

>%wc myfile
>     3     6    36   myfile
>
>%wc myfile > myfile
>%cat myfile
>     0     0     0   myfile
>
>How come MYFILE becomes that?

because the original "myfile" gets overwritten by the new "myfile"
(from the redirection) by the shell BEFORE wc is run, therefore,
the only thing wc sees is an empty file.



--

Thanks,
Steve.                    sfreed@ariel.unm.edu

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