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Re: option abbreviation exceptions

From: Andrew McGill
Subject: Re: option abbreviation exceptions
Date: Tue, 6 Jan 2009 07:31:46 +0200
User-agent: KMail/1.9.9

On Tuesday 30 December 2008 15:00:18 Eric Blake wrote:
> According to Pádraig Brady on 12/30/2008 2:46 AM:
> >> Usage: truncate [OPTION]... [FILE]...
> >
> > Is supporting stdin a useful enhancement?
er ...
> > Maybe if you can get the shell to open
> > different files based on some condition,
> > though again that seems a little contrived.
> if cond ; then
>   foo=file1
> else
>   foo=file2
> fi
> truncate -s0 <$foo
This redirection is wonderful, but entirely counter-intuitive.  By convention 
stdout is where writes occur, stdin is where reads occur.  Modifying the file 
given as stdin is just a little unexpected.  

For good measure (all?) shells open stdin as read-only, which makes the 
operation fail -- ftruncate(0,0) gives "invalid argument".  The redirection 
you need for a writable stdin under bash seems to be this one:
  truncate -s$SIZE 0>>$foo


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