Git Cheatsheet

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Revision as of 15:56, 1 October 2013 by Brads (Talk | contribs) (A Cheat Sheat for How To Use Git)

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A Cheat Sheat for How To Use Git

I, Bob M., got this from Brad Sawatzky in response to an e-mail.

The main thing to remember about git is that it is local (ie. on your
machine).  Checkouts are from your local copy, and commits are to your
local copy -- you get to choose when and in what way you push your
changes upstream (more on this later).

Since you are only committing to your local copy, you can commit
incomplete and/or non-working code with impunity.  Once you have a
feature that is working, you can build and push the associated set
of changes up to Ole.

It's impossible to lock people out of a repo the way you can with
cvs/svn -- git is specifically designed to remove that problem.

[Re: github authentication]
You always have to authenticate before pushing changes upstream.
Uploading a key just means you don't have to type in your password
every time you push upstream.  (Note that you do not, and should not,
push every change you make upstream right away.)
  https://help.github.com/articles/generating-ssh-keys

I find git to be *way* more lightweight (in the ease of use sense) than CVS,
but it does require a change in how you think about version control.  I
created and used 8 independent (local) git repos last week alone while I was
debugging a DAQ.


Here are the commands I use 99% of the time:

  1) Create your repo 
  git init            : create empty repo from scratch
  git add .           : add everything in this directory
  git commit -m'initial commit'  : initialize the repository
  -- OR --
  git clone <URL>     : copy a repo from elsewhere

  -- Useful commands:
  git log             : see the log file (can do this anytime)

  2) Work on your code inside a new branch:
  git branch my-working-topic      : create a branch
  git checkout my-working-topic    : change into that branch
  <hack away until I have something that I want to store as a 'change'>
  - Branches are nice because the isolate your present work from other
    (possibly conflicting) changes in your repo.  You can move from one branch
    to another to work on different things, or try out different (conflicting)
    ways to solve a given problem.

  - Useful commands at this stage:
  git checkout foo.c   : retrieve a 'fresh' copy of foo.c, replacing my
                         borked version
  git stash            : stores un-committed changes in your working directory
                         - useful if you want to switch to different branch but
                           have local modifications that you don't want to
                           commit just yet

  3) Build a 'commit'
  -- Repeat these as often as you want:
  git add -p          : 'interactively' ask about what I changes I want to
                        record as part of this commit
  git add <file>      : just add all changes in a given file (or add a new
                        file)

  - Misc commands that are useful at this stage:
  git status          : summary of changed files
  git diff --cached   : review the commit you've been working on with
                        'git add'
  git diff            : see diff of changes made since the last commit
                        that are *not* in commit you're working on
  git reset HEAD      : blow away the commit you've worked on with
                        the 'git add's.  Nothing changes in your
                        directory -- you just start at the beginning of
                        step 3 again.
                        I think 'git undo' is a shortcut for this.

  4) Save the commit
  git commit          : save the change set with a notation in the log
  git commit --interactive  : gives you a chance to edit the changeset
                      you built in (3) without having to 'git reset
                      HEAD' and start from scratch

  5) goto (2) and repeat until you have something that you want to send
     upstream
    git fetch      : this pulls the changes to your machine, but does
                     NOT change your working directory at all
    git merge      : this will attempt to merge your present state with
                     the upstream <HEAD>.  You will need to resolve
                     conflicts at this point
    -- OR --
    git pull      : basically shorthand for a 'git pull' followed by a
                    'git merge'rd as part of this change

  6) Merge upstream
    - Talk to Ole the first time you do this -- there are many ways to
      handle this.

    One method (this is the most flexible way, but you guys might be
    pushing to a personal branch instead of a personal repo):

    git push      : this will transfer the changes from your local
                    working copy up to the github repo you cloned from.
       - You can then send a 'pull request' to Ole, OR ask that he merge
         your branch to master.  

  7) goto (2)

Recommended quick references:

 http://www-cs-students.stanford.edu/~blynn/gitmagic/ch02.html
 http://schacon.github.io/git/everyday.html
 Graphical cheatsheet: 1 page reference


 A compilation of links I've found useful:
 https://hallcweb.jlab.org/wiki/index.php/Git_Howto