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Re: cp/mv: add -n option to not overwrite target (Ubuntu bug #229182)

From: Jim Meyering
Subject: Re: cp/mv: add -n option to not overwrite target (Ubuntu bug #229182)
Date: Wed, 07 Jan 2009 17:08:04 +0100

Kamil Dudka <address@hidden> wrote:
> On Wednesday 07 January 2009 08:35:24 Jim Meyering wrote:
>> Have you considered other long-option names?
>> I prefer --no-clobber.  or maybe --no-overwrite
> In this case I prefer --no-overwrite, but feel free to change it.

Hi Kamil,

--no-clobber gets a few more matches in C sources than --no-overwrite,

  57  http://www.google.com/codesearch?q=\-\-no\-clobber+lang:c
  40  http://www.google.com/codesearch?q=\-\-no\-overwrite+lang:c

Regarding uses, it appears to outnumber --no-overwrite 2-to-1.

Anyone else have a preference?

>> -----------------------
>> Please adjust the NEWS entry:
>> -  cp/mv new option -n to not overwrite target
>> +  cp and mv accept a new option, --LONG_OPTION (-n): silently refrain
>> +  from overwriting any existing destination file
>> -----------------------------
>> You haven't mentioned how this new option interacts with --backup,
>> another option that prevents loss of any existing destination file.
>> Since with --backup, cp and mv arrange to move any destination aside,
>> one might expect -n --backup to be equivalent to --backup.
> The behavior is the same as for -i option with negative user's response. If
> nothing is going to be overwritten, there is nothing to backup. I think this
> is an expected behavior and in this way is the --backup option already
> documented.

My point is that depending on when you test for
the existence of the destination file, you could say that with
--backup, there is never an existing destination file, since
it's always moved aside before the "open".  In *that* case,
you would expect the "-n" in "--backup -n" to be ignored.
This ambiguity is why the semantics of "--backup -n" must be
documented explicitly.

Since there are three copies of that new sentence in coreutils.texi,

    If you specify more than one of the @option{-i}, @option{-f},
    @option{-n} options, only the final one takes effect.

would you please put it in a macro?

Thanks for being patient.

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