some git usage related queries

[Saifi Khan]

Hi:

Here are some git usage related newbie queries.

1. i read a notification about a new commit 
   eg. pkgsrc commit 
   http://gitweb.dragonflybsd.org/pkgsrc.git/commit/4ceab3c0055ed6bdacff399294ff8ef253b99468

   Since i maintain a local git repo for pkgsrc, i'd like to
   know the diff between what i got and what's in the latest
   commit.

   What command do i run locally to see the diff ?


2. i've pulled in latest commits using 'git pull'.
   While working with local repository, i want to
   know the diff between the last commit and the latest commit
   for a given file eg. nrelease/Makefile.

   what i tried doing was:
   # cd /usr/src
   # cd nrelease
   # git diff HEAD^ HEAD ./Makefile
   #

This doesn't work. What is the correct approach here ?


3. after pulling in the changes related to Sascha's commit eg.
   
   when i tried this command:
   # git describe 5623ae32853fcfb747f493ea6af0059a56fb9b56
   v2.5.1-200-g5623ae3

This doesn't show up the details of the commit. What would be
the appropriate command to use ?


4. i apply some patches to a given file
   eg. Stathis' patch for mq*() syscall for MPSAFE

   # cd /usr/src
   # fetch http://leaf.dragonflybsd.org/~beket/mq-mpsafe.diff
   # git apply mq-mpsafe.diff

   Ideally i should have created a branch and then apply the
   patch. However, i applied the patch to the master.
   Some new files are created and some .bak files created.
   When i 'git pull' next, there are issues.

   What is a good practice to adopt here ?

   Is there also something as 'unapply' a patch in git ?


i've readup Pragmatic version control with Git and GitUsage
documentation in the wiki. So, while i can get around with basic
Git commands, i'm still facing issues.  

i'd be grateful, if some of experienced folks on the project can
share their nuggets of wisdom on this. Thanks for any help.


thanks
Saifi.