advanced-git.md

Advanced Git - Functionality and Features

Brent Laster, SAS

Agenda

• core concepts refresh
• merging and rebasing
• stash
• reset and revert
• rerere
• bisect
• worktrees
• subtrees
• interactive rebase
• notes (a way to augment the commit without altering the commit itself)
• grep

Centralized vs distributed VCS

Centralized has a server which has to be connected.

distributed has everything local, like bazaar, hg, & git

Git in One Picture

 public remote repository             {server}
  ^
 prod   local repository (commit to)  {
  ^
 test   staging area                   local machine
  ^
 dev    working directory             }

Git granularity (what is a unit?)

• traditional source control is usually a file
• in Git, the unit is a tree

Merging: what is fast forward

git checkout master
git merge hotfix

C0 <- C1 <- C2 <- C4
             \
              --- C3

3 way merge

Takes C2, C4, C5 and creates a merge commit for C6

C0 <- C1 <- C2 <- C4    C6
             \
              --- C3 <- C5

Merging: what is a rebase?

Merge with history

                  master
C0 <- C1 <- C2 <- C4
             \
              --- C3 <- C5

C0 <- C1 <- C2 <- C4 <- C3' <- C5'
             \          /
              --- C3 <- C5

Command: git stash

Takes work in progress and puts it in a staging area, and cleans out your area back to the last commit

• git stash -u -- stashes even untracked files

• git stash save "cool feature comment"

• git stash apply stash@{1} - will put that stash back into your working area, I can pick any one from the list.

• git stash pop stash@{2} - will take it out of the stash and puts it back into your working area.

Git reset

Like a rollback and puts you back to a previous commit warning: --hard overwrites everything

Moves the branch pointer back

git revert

More of an undo vs rollback (reset). Revert tries to cancel out the changes. Adds a new commit that cancels out the changes of the commit I am reverting

git rerere

reuse recorded resolution

teaching git when I see a conflict like this do it like this

enabled via in gitconfig rerere.enabled = 1

git rerere 1

git checkout master
git config -global rerere.enabled 1
git merge feature -- during a conflict puts it into a staging area, but you have
            to resolve the conflicts

With rerere on, it records before you fix the conflict.

fix conflicts
git add .
git commit -m "finalize merge"

if you have the rerere, git records a post image after you resolved the conflict. What is this good for?

Git rerere 2

git reset --hard HEAD~1
git checkout master
git merge feature
   Merge conflict in "File B"
   Resolved 'File B' using previous resolution

git bisect

binary search

switching branches

worktrees

multiple branches without cloning several clones. git worktree,

separate working directories tied back to the same working repositories

 remote repository
 local repository (commit to)
 staging area
 working directory

 git worktree add -b exp tree1
 git worktree add -b prod tree2

subtrees

git subtree add, allows including a acopy of a separate repository with your current repository.

notes:

• no links like a submodule - just a copy in a subdirectory
• advantage - no links to maintain
• disadvantage - extra content to carry around with your project

Subtree overall view

                  parent project  \
subtree \                      proj_dir
     proj_dir/mod1

subtree - adding a project as a subtree

git clone foo.git myproject

interactive rebase

git rebase -i (I already use this)

notes

git notes - add additional information to objects in the git repo or look at such information

use case - at some point after making a commit, you may decide that there are additional comments or other non-code information that you'd like to add with commit

create a note - git notes add -m "this is an example of a note" 2f2ea1e

show a note - git notes show 2f2ea1e

git grep

git grep - similar options to grep