pre-receive hook ; how to detect file and append code ?

> Dear list,
>
> How can I detect a specific file during push, if it is modified or not ?
> And how can I then append a block of code into that file; if modified
> during push ? I think pre-receive hook is the best for this operation.

> "J. Bakshi" <joydeep.bakshi@infoservices.in> writes:
> 
> > How can I detect a specific file during push, if it is modified or not ?
> > And how can I then append a block of code into that file; if modified
> > during push ? I think pre-receive hook is the best for this operation.
> 
> The purpose of the "pre-receive" hook is to either approve or reject
> a proposed change made by the push.  When it runs, the repository
> already has received all the objects necessary to inspect the
> proposed change locally (from the receiving repository's point of
> view).
> 
> A proposed change comes in the form of <old> <new> <refname> that
> says "The pusher saw <old> at <refname> when he started this push,
> and it wants to update the ref to <new>".  So any of the following
> standard techniques (note: not exhaustive) to inspect the changes
> between <old> and <new> can be used:
> 
>     # are log messages sane?
>     git log <old>..<new>
> 
>     # are the changes sane?
>     git diff <old>..<new>
> 
>     # does it leave forbidden paths intact
>     git diff --name-only <old>..<new>
> 
> If your script likes the proposed change, exit with 0.  If it does
> not, exit with non-zero.
> 
> That is all it can do.  It is not supposed to change <new> to some
> other value, and there is no interface to do so.
> 
> If you want to rewrite the history pushed into the repository after
> a push is accepted, you would want to run it from post-receive or
> something.  All the usual warning about rewriting published history
> will apply if you do so, however.  After all, the history is already
> published immediately before post-recieve (or post-update) runs.