commitinfo - information about committed files

[Moray B. Grieve]

When I modify the commitinfo file to perform a check prior to a commit matching 
a regular expression, what information about the file can I obtain from the 
program executed?

As far as I can see all that is passed into the executable is the location of 
the directory, and a list of files being committed. Can I 

a) find out what branch the file is being checked into
b) modify the contents of the file before the commit 

I have a remote repository and all checkins occur via a client.

With many thanks for any feedback,

Moray Grieve