Git Theory

The revision Graph

Revisions form a GRAPH

import os
top_dir = os.getcwd()
git_dir = os.path.join(top_dir, 'learning_git')
working_dir=os.path.join(git_dir, 'git_example')
os.chdir(working_dir)

%%bash
git log --graph --oneline

* 5f73fff Merge branch ‘master’ of github.com:UCL/github-example

|\

| * 3c4a02f Add another Beacon

* | a5f66ac Add Glyder

|/

* 54a5484 Merge branch ‘master’ of github.com:UCL/github-example

|\

| * b3d5585 Add a beacon

* | b7eba49 Translating from the Welsh

|/

* 4bc25e9 Merge branch ‘master’ of github.com:UCL/github-example

|\

| * aed6a4d Add Scotland

* | d7d7243 Add wales

|/

* 79b1285 Add Helvellyn

* cdd35b8 Include lakes in the scope

* 76322e5 Add lakeland

* e533bb0 Revert “Add a lie about a mountain”

* 972c8ed Change title

* 04ada3b Add a lie about a mountain

* 03915a3 First commit of discourse on UK topography

Git concepts

• Each revision has a parent that it is based on
• These revisions form a graph
• Each revision has a unique hash code
  • In Suleman’s copy, revision 43 is ab3578d6
  • Jane might think that is revision 38, but it’s still ab3579d6
• Branches, tags, and HEAD are labels pointing at revisions
• Some operations (like fast forward merges) just move labels.

The levels of Git

There are four Separate levels a change can reach in git:

• The Working Copy
• The index (aka staging area)
• The local repository
• The remote repository

Understanding all the things git reset can do requires a good grasp of git theory.

• git reset <commit> <filename> : Reset index and working version of that file to the version in a given commit
• git reset --soft <commit>: Move local repository branch label to that commit, leave working dir and index unchanged
• git reset <commit>: Move local repository and index to commit (“–mixed”)
• git reset --hard <commit>: Move local repostiory, index, and working directory copy to that state

Next: Reading - Branches