Re: How to overwrite a symbolic link?

[Eric Blake]

On 05/07/2010 09:31 AM, Peng Yu wrote:
> On Fri, May 7, 2010 at 10:16 AM, Eric Blake <eblake@redhat.com> wrote:
>> On 05/07/2010 09:02 AM, Peng Yu wrote:
>>> Suppose I need to modify one primary file slightly to do something a
>>> little bit different. But I still need to do the original job,
>>> therefore I need to keep it the original M files. I can copy the whole
>>> directory and then modify one file in the newly copied N files. But
>>> I'll lose track of which file has been changed later on, which is
>>> important to me.
>>
>> Consider using a version control system.  Track the contents of your
>> directory under your favorite VCS, like git, and then you can use
>> version control commands to generate the delta for both primary and
>> secondary files across any state that you committed.
> 
> I can't use version control for
> 1. I need to frequently change file names.
> 2. Both primary and secondary files could be of hundred of MB or even GB.

git handles both of those situations, without too much hassle.

>> But overloading bash's > and >> operators is not possible.
> 
> Is it because the underlying library that used in bash doesn't support
> the semantic of symbolic link that I propose? Or it is because of the
> OS?
> 
> Is it possible to modify source code of bash to change the semantics
> of symbolic link.

Yes, it's possible to modify the source of bash to change how bash
treats symlinks when using the > operator.  But I would advise against
it, as your fork of bash would no longer comply with POSIX, and would
probably break a lot more than it fixes.  Rather, if you insist on
modifying bash, consider adding a new operator (maybe spelled '>;',
similar to the noclobber override spelling of '>|'), so that your use of
the new operator is explicit that you know what you are doing in your
scripts (if the operand of the new operator is a symlink, break the
symlink and create a file in its place instead of operating on the
target of the symlink).

-- 
Eric Blake   eblake@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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