GIT introduction

Heads Up

Git is a distributed version control and source code management (SCM) system width an emphasis on speed.

Under the hood

.git directory


		HEAD
		config
		description
		hooks
		index
		info
		objects
		refs


						
	[hh git-basics :) ]$ ls  .git/objects/
	02	15	25	35	41	50	62	6b	72	80	89	96	a3	af	bc	c8	de	f4	fd
	04	17	26	36	42	55	63	6c	73	82	8a	9a	a6	b0	c0	ca	e0	f6	ff
	05	1d	29	3c	44	59	67	6e	77	84	90	9d	a7	b6	c2	cc	e1	f8	info
	11	20	2d	3f	47	5a	68	6f	78	87	93	9e	ad	b8	c3	d0	e6	f9	pack
	12	24	2e	40	49	5d	69	71	7e	88	95	9f	ae	b9	c4	d1	e9	fa

	[hh git-basics :( ]$ ls .git/objects/3c/
	cf65ae409bb502812244a3a4585ae32bc9fb7d

config: contains your project-specific configuration options
description: only used by the GitWeb program
info: keeps a global exclude file for ignored patterns that you don’t want to track in a .gitignore file
hooks: contains your client- or server-side hook scripts

HEAD: points to the branch you currently have checked out
index: is where Git stores your staging area information
objects: stores all the content for your database
refs: stores pointers into commit objects in that data (branches)

Objects


[hh reveal.js :) ]$ git lg
* 774b933 - (HEAD, master) First steps (16 minutes ago) <Mikhail Vnukov>
* 8831469 - Initial (11 hours ago) <Mikhail Vnukov>


[hh reveal.js :) ]$ git cat-file -t 774b933
commit


[hh reveal.js :) ]$ git cat-file -p 774b933
tree 3ccf65ae409bb502812244a3a4585ae32bc9fb7d
parent 883146996813919dd3d8f35728d05e42fd070a62
author Mikhail Vnukov <mikhail.vnukov@gmail.com> 1372653800 +0400
committer Mikhail Vnukov <mikhail.vnukov@gmail.com> 1372653800 +0400

First steps


[hh reveal.js :) ]$ git cat-file -p 3ccf65ae409bb502812244a


100644 blob 9ffdbc7345be803854e777dd7183dbe76153ae47	.gitignore
100644 blob 2d6cd8f4f425afc2f026172851b172151b9f8f3e	.travis.yml
100644 blob 892469a4e40641af1bf57d292a71e5c28b7373a7	Gruntfile.js
100644 blob e1e8bf7a8c29fe02e278aba9f7c5658e3b474590	LICENSE
100644 blob 96b7c0e966f4ffe7ad188b82d7ae9c5caaf42a06	README.md
040000 tree 6814ad1c3d2a3b8eb087d017a8c00a7c26c370cd	css
100644 blob 02f8e62584213205a025a0ebfeaf20eca0dbcf92	index.html
040000 tree f6ddefee310758a129784ff5d68e1c7085041538	js
040000 tree a630c3d86f33c9b73712c74c2e8c602e5b884f3c	lib
100644 blob c2e6d3da8f7d84db93aae4daca467f9b34eb3b2f	package.json
040000 tree 0595ca9d9b4cd568541583bf15c3b595ddc43779	plugin
100644 blob bc6197e3dc1e19ec90ae353d142b177e37a89864	reveal.sublime-project
040000 tree b9c5bb7ed230640cdf846c30b06c23c692f24d44	test

Branches


[hh git-basics :) ]$ ls .git/refs
heads	remotes	tags

heads = branches


	[hh git-basics :) ]$ ls .git/refs/heads/
	gh-pages	master


	[hh git-basics :) ]$ git branch
	* gh-pages
	  master

remotes = remote branches


[hh git-basics :) ]$ ls .git/refs/remotes/origin/
gh-pages


[hh git-basics :( ]$ git branch -a
* gh-pages
  master
  remotes/origin/gh-pages

HEAD = current branch


[hh git-basics :) ]$ cat .git/HEAD
ref: refs/heads/gh-pages

Abstractions

Branches

Branches are just references to commits.


	[hh git-basics :) ]$ git checkout -b part2


[hh git-basics :) ]$ git checkout -b abstractions
[hh git-basics :) ]$ git commit -am "Started abstractions chapter"


[hh git-basics :) ]$ git checkout part2
[hh git-basics :) ]$ git commit -am "Added funny image to the chapter2"

Remote branches

Remote branches are references to the state of branches on your remote repositories. They’re local branches that you can’t move


[hh git-basics :) ]$ git push origin gh-pages
[hh git-basics2 :) ]$ git fetch


[hh git-basics2 :) ]$ git checkout gh-pages						
[hh git-basics2 :) ]$ git merge

Branching

Create branch


$ git branch iss53
$ git checkout iss53


$ git checkout -b iss53

Remove branch


$ git branch -d iss53

Remote branches

Create


$ git push origin serverfix


$ git push origin serverfix:serverfix

Remove


$ git push origin :serverfix

Merge

Fast-forward


[hh test :) ]$ git checkout fix
Switched to branch 'fix'
[hh test :) ]$ git merge fix2
Updating d808d3c..2e257a5
Fast-forward
 file2   |   0

Three-way merging


[hh test :) ]$ git checkout master
Switched to branch 'master'
[hh test :) ]$ git merge fix


CONFLICT (modify/delete): tmp.dot deleted in HEAD and modified in fix. Version fix of tmp.dot left in tree.
CONFLICT (modify/delete): out.png deleted in HEAD and modified in fix. Version fix of out.png left in tree.
Automatic merge failed; fix conflicts and then commit the result.


[hh test :) ]$ git mergetool
Merging:
out.png
tmp.dot


Deleted merge conflict for 'out.png':
  {local}: deleted
  {remote}: modified file
Use (m)odified or (d)eleted file, or (a)bort? m


						
Deleted merge conflict for 'tmp.dot':
  {local}: deleted
  {remote}: modified file
Use (m)odified or (d)eleted file, or (a)bort? m


						
[hh test :) ]$ git status
# On branch master
# All conflicts fixed but you are still merging.
#   (use "git commit" to conclude merge)
#
# Changes to be committed:
#
#	new file:   out.png
#	new file:   tmp.dot
#


[hh test :) ]$ git commit
[master 022112e] Merge branch 'fix'

Rebase

tough on grease, but soft on history


[hh test :) ]$ git checkout branch1
Switched to branch 'branch1'
[hh test :) ]$ git rebase master
First, rewinding head to replay your work on top of it...
Applying: Second commit
Applying: Third commit


[hh test :) ]$ git checkout master
Switched to branch 'master'
[hh test :) ]$ git merge
fatal: No commit specified and merge.defaultToUpstream not set.
[hh test :( ]$ git merge branch1
Updating 5a467b4..cb50365
Fast-forward
 file2 | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 file2

Do not rebase commits that you have pushed to a public repository

Git workflow

Short work


git checkout -b private_feature_branch
touch file1.txt
git add file1.txt
git commit -am "WIP"


git checkout master
git merge --squash private_feature_branch
git commit -v


git push
git branch -d private_feature_branch

Long work


git checkout -b private_feature_branch
touch file1.txt
git add file1.txt
git commit -am "WIP"
...
git commit -am "WIP"
..
git commit -am "WIP"


git rebase --interactive master

Troubleshooting

Undoing things

Changing last commit


$ git commit --amend


$ git commit -m 'initial commit'
$ git add forgotten_file
$ git commit --amend

Unstaging a Staged File


$ git add .
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       modified:   README.txt
#       modified:   benchmarks.rb
#


$ git reset HEAD benchmarks.rb
benchmarks.rb: locally modified
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       modified:   README.txt
#
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#       modified:   benchmarks.rb
#

Unmodifying a Modified File


# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#       modified:   benchmarks.rb
#


$ git checkout -- benchmarks.rb
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       modified:   README.txt
#

But sometimes we need to UNDO something

Remove commit in history


[hh test :) ]$ git lg
* f246686 - (HEAD, master) commit4 (5 seconds ago) <Mikhail Vnukov>
* 12d18ef - commit3 (16 seconds ago) <Mikhail Vnukov>
* c82f557 - commit2 (30 seconds ago) <Mikhail Vnukov>
* 8cc0647 - commit1 (40 seconds ago) <Mikhail Vnukov>

We are going to remove commit2 - c82f557


[hh test :) ]$ git rebase -i HEAD~3
Successfully rebased and updated refs/heads/master.


pick c82f557 commit2
pick 12d18ef commit3
pick f246686 commit4

# Rebase 8cc0647..f246686 onto 8cc0647
#
# Commands:
#  p, pick = use commit
#  r, reword = use commit, but edit the commit message
#  e, edit = use commit, but stop for amending
#  s, squash = use commit, but meld into previous commit
#  f, fixup = like "squash", but discard this commit's log message
#  x, exec = run command (the rest of the line) using shell
#
# These lines can be re-ordered; they are executed from top to bottom.
#
# If you remove a line here THAT COMMIT WILL BE LOST.
#
# However, if you remove everything, the rebase will be aborted.
#
# Note that empty commits are commented out