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2002 Jun 13 16:41

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Re: [vox] cat and >> - how does it know?
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Re: [vox] cat and >> - how does it know?



File locking?

-Mark


On Thu, 13 Jun 2002, nbs wrote:

>
> Not paying attention to tab-completion, I just accidentally did this:
>
>   cat somefile >> somefile
>
>
> Luckily, "cat" noticed, and complained:
>
>   cat: somefile: input file is output file
>
>
>
> But - how does it know?  Using just argv/argc, all "cat" would know
> is that you want to throw "somefile" to stdout.
>
> The shell is the one worrying about the ">>" and everything after it.
>
>
> I'm guessing the shell makes a note of what it's doing (redirecting/appending)
> and makes that info. available to the process (in this case, cat),
> who can notice and, in this case, complain.
>
>
> How, exactly, does it do this?
>
>
> -bill!
> (too lazy to dig up source to /bin/cat ;) )
> PS - This was under both tcsh and bash
> _______________________________________________
> vox mailing list
> vox@lists.lugod.org
> http://lists.lugod.org/mailman/listinfo/vox
>

--
Mark K. Kim
http://www.cbreak.org/
PGP key available upon request.

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