Immutability

• git holds information in commit objects
• once a commit object is created it cannot be changed

• but there is git amend you say

$ git commit -m "The bets commit message ever."
[master 57d9fc9] The bets commit message ever.
 1 file changed, 1 insertion(+)
 create mode 100644 foo

$ git commit --amend
[master 59a5de1] The best commit message ever.
 Date: Wed Apr 13 00:25:41 2016 +0300
 1 file changed, 1 insertion(+)
 create mode 100644 foo

Here's what happens

Pull vs fetch

• at heart they both fetch remote metadata
• pull also updates the working directory
• fetch only updates the metadata

$ git rev-parse --abbrev-ref @{u}

To see what is the configured remote branch for the current branch

OR

$ cat .git/config 

... and search for your branch

$ git pull --rebase

Pull can also rebase instead of merge

Rebase vs merge

Merging

http://rypress.com/tutorials/git/media/5-1.png

Merging

• creates merge commit
• non-destructive operation
• doesn't modify history
• but history will be uglier

Merging

git checkout feature
git merge master

git merge master feature

Rebasing

http://rypress.com/tutorials/git/media/4-1.png

Rebasing

• Moves all the commits on top of other branch
• Rewrites history
• Creates brand new commits(remember immutability) 
• No more merge commit => clean history

Interactive Rebasing

• Eliminate unwanted commits
• Even cleaner history

http://rypress.com/tutorials/git/media/5-5.png

Interactive Rebasing

git checkout feature
git rebase -i master

pick 33d4a7a Commit message #1
pick 9543b3d Commit message #2
pick 5c87661 Commit message #3

pick 33d4a7a Commit message #1
fixup 9543b3d Commit message #2
pick 5c87661 Commit message #3

Interactive Adding

$ git add -i

           staged     unstaged path
  1:    unchanged        +2/-2 file1
  2:    unchanged        +1/-1 file2.php

*** Commands ***
  1: status	  2: update	  3: revert	  4: add untracked
  5: patch	  6: diff	  7: quit	  8: help
What now> 

Golden Rule

Never ever use rebase on public branches

Hashes, refs and reflogs

Hashes

• 40 characters long SHA-1

​

• most direct way to identify commits
• can be specified partially
• to resolve the hash of a branch :

4b825dc642cb6eb9a060e54bf8d69288fbee4904

git rev-parse master

commit 5584ba46f089c7389d9fbf7b1d371e468394bb84
Author: Web Developer <web@developer.com>
Date:   Thu Apr 7 00:18:06 2016 +0300

    Commit message details

Refs

• user-friendly alias to commit hash​
• stored in .git/refs

.git/refs/
    heads/
        master
        feature
    remotes/
        origin/
            master
    tags/
        v0.1

Reflogs

• timecapsule
• kept for 90 days by default

$ git reflog
59a5de1 HEAD@{0}: commit (amend): Commit message #1.
57d9fc9 HEAD@{1}: commit (initial): Commit message #2.

$ git checkout HEAD@{1}

$ git reset --hard HEAD@{1}

Git hooks

• local / user hooks
• server hooks
• hook into git's workflow
• they live in .git/hooks
• you can write them in any scripting language

#!/bin/sh

#!/usr/bin/env python

Local / user hooks

• pre-commit
• commit-msg
• post-commit
• ...

Server hooks

• pre-receive
• update
• post-receive
• ...

Git Template

• used to populate .git folder
• enable custom hooks by default

$ git config --global init.templatedir 'templatedir'

The power of logs

Pretty Logs

$ git log --graph --oneline --decorate
* 7a48ea2 (HEAD, master) Commit message #5.
* 075ce36 Commit message #4.
*   62cbf27 Merge branch 'branch'
|\
| * 5a40d5a Commit message branch#2.
| * dd0109a Commit message branch#1.
* |  dd0f5d6 Commit message #3.
|/
* 13d1b4b Commit message #2.
* 45de2f7 Commit message #1.

Some visual tools : gitg, gitk, SourceTree

Shortlog

$ git shortlog
Penguin (2):
      Added going for a swim feature.
      Fix not working leg.

Archibald (3):
      Added some voodoo magic.
      Merge branch 'fix_leg'.
      Playing with basic magic config.

Filtering logs

$ git log sincerev..untilrev --summary --diff-filter=D

get all the files that were deleted between two revisions

$ git log --after="2016-4-1" --before="2016-4-12"

get commits between specific dates

$ git log --merges

get only comits with at least two parents

Some sugar and spice

locate bug introducing commit

$ git bisect

see diff from staged files

$ git diff --cached

get commit from different branch

$ git cherry-pick sha1

safe revert public commit

$ git revert

Aliases

setup shortcuts for your favourite commands

$ git config --global alias.visual '!gitk'

$ git config --global alias.unstage 'reset HEAD --'

$ git config --global alias.history 'log --graph --oneline --decorate'

$ git config --global alias.pr 'pull --rebase'