1. Learning GIT
CodicePlastico.com

2. Why source control? Working fearless Experimenting Collaborating
Version tracking
:-) Blame someone :-)
Zip files
Deployment

3. What’s inside? All you need to run your project: Source code
Build scripts
Database scripts
Tests
Assets

4. What’s outside? External libraries
Generated stuff: binaries, compiled CSSs, minified/bundled JSs, generated documentation, …
IDE configuration settings (.vs, .idea, .settings, .project, …) …

5. Agenda Introduction to Git Obtaining and installing Git
Basic Git operations
Configuration
Working with local repository
Branches and Merges
Remote repositories

6. Agenda
Submodules
Daily use
Helpful commands

7. Git
Built by Linus Torvalds and Linux community as an alternative to BitKeeper
Developed starting from 3 april 2005
Release 1.0 on 21 december 2005
What it is, philosophy, history

8. Goals Facilitate Distributed Development
Scale to handle thousands of developers
Perform quickly and efficiently
Maintain integrity and trust
Enforce accountability. (who did what and why)
Immutability
What it is, philosophy, history

9. Goals Atomic transactions Support and encourage branched development
Complete repositories
Clean internal design
Be free

10. Obtaining & installing Git

11. What you get?

12. Quick intro…
Demo di creazione di un nuovo repo e di aggiunta di un nuovo file

13. how svn works

14. how git works

15. Basic Git concepts Repositories Blobs Trees Commits Tags Index
Workspace, index, trees, blob

16. Repositories Is the database of your project
It provides a complete working copy of all the files in the repository and the copy of the repository itself
It maintains two primarily data structures: object store and index.
Everything is inside the .git folder

17. Blobs It contains the data of the files
Each version of a file is represented as a blob
It does not contains any metadata

18. Trees It contains one level of directory information
It records blob identifiers, path names
It can contains other trees

19. Commits
Contains metadata of each change introduced into the repository
Each commit points to a tree object and captures in one complete snapshot the state of the repository at the time the commit was performed

20. Commits A commit contains:
The name of a tree object that actually identifies the associated files
The name of committer and the time
The commit message
author and committer are usually the same

21. Tags
Assign a readable name to a commit

22. Index
Captures a version of the project’s overall structure at some moment in time
It’s a layer between the working directory and the repository that tracks the files
It doesn’t contains any file content

23. Content-addressable Names
Git tracks content
Each object has unique name produced applying SHA1 to the content
The object store is based on the hashed computation of the contents of its objects
If two separate file have the same content git store a single copy of them
Git store every version of every file (not their difference)
Two identical file have the same SHA1 whatever the names of the files are.

24. Object Store
commit
09a0473
master
tree
blob1
blob2

25. A commit later… commit 09a0473 commit 11cf9410 master tree tree blob1

26. Inside the .git dir total 40
-rw-r--r ema staff 22B May 17 13:37 COMMIT_EDITMSG
-rw-r--r ema staff 23B May 17 13:35 HEAD
drwxr-xr-x 2 ema staff 68B May 17 13:35 branches
-rw-r--r ema staff 137B May 17 13:35 config
-rw-r--r ema staff 73B May 17 13:35 description
drwxr-xr-x 11 ema staff 374B May 17 13:35 hooks
-rw-r--r ema staff 104B May 17 13:37 index
drwxr-xr-x 3 ema staff 102B May 17 13:35 info
drwxr-xr-x 4 ema staff 136B May 17 13:37 logs
drwxr-xr-x 7 ema staff 238B May 17 13:37 objects
drwxr-xr-x 4 ema staff 136B May 17 13:35 refs

27. File classification
Tracked: already in the repository or staged in the index.
Ignored: a file that git ignore because it is in the .gitignore list
Untracked: a file that is not in the other two categories.

28. Demo… Change file status by creating it, adding it to the stage….
git add, rm, mv

29. git add
Add the file contents to the index
git add filename

30. git rm Remove files from the working tree and from the index
git rm filename

31. git mv Move or rename a file, a directory, or a symlink
git mv filename

32. git commit –m ”a message”
Record changes to the repository
git commit –m ”a message”

33. basic operations

34. .gitignore

35. Inside a commit A git commit is used to record changes to a repository
git commit -m “refactoring”
Git creates
new blobs for any file that has changed and
new trees for any directory that has changed
reuse any blob or tree that has not changed
pag 44

36. Inside a commit Every commit is atomic Every commit has a name
4eff6f95a00dbadb469e751b3b9bceb0b40159d5
HEAD is the last commit / the “tip” (of the current branch…)

37. Relative commit name Git uses relative name for commits: HEAD~1 HEAD~2
HEAD~N

38. Viewing the history
Git log shows the commit history (by default, on the current branch) git log git log –-oneline git log –-graph –-all –decorate \ --oneline …

39. Git log Some useful options: --pretty: different format
--graph: show the branch graph
git log --pretty=format:'%C(yellow)%h %Cred%ad %Cblue%an %Cgreen%d %Creset%s' --date=short -- graph
pretty: oneline, short, medium, full, fuller, , raw

40. Git blame
Who did it?
git blame filename
git blame filename

41. Branches A branch can represent an individual customer release
A branch can encapsulate a development phase
A branch can isolate the development of a single feature
A branch can represent the work of an individual contributor

42. master branch Every git repository has (usually) the master branch
It’s not special and can be deleted (if needed)
it’s the trunk

43. Using branches There is at most one current branch
HEAD represent the most recent commit (‘tip’) on the current branch

44. git branch name [starting_commit]
Creating branches
git branch name [starting_commit]
It just introduce the name of the commit in the repo

45. Checking out branches
git checkout name

46. Creating and checking out
git checkout –b name [starting_commit]

47. Checking out branches
Files and directories present in the branch being checked out but not in the current branch are checked out of the object store and placed into your working tree.
Files and directories present in the current branch but absent in the branch being checked out will be removed from the working tree
Files common to both branches are modified to reflect the content present in the checked out branch

48. Uncommitted changes
Files and directories in the working directory that are not being tracked are left alone
If there are local modification to a file that are different from changes that are present on the new branch, git issue an error message
-f force the checkout discarding changes
-m merge the changes to the new branch

49. Deleting branches
git branch -d name

50. Deleting branches The current branch cannot be deleted
Git won’t allow you to delete a branch that contains commits that are not also present on the current branch (use -D instead of -d to force it)

51. Tagging
A tag is meant to be a static name that does not change over time
Useful to mark versions:
git tag -a v1.2 -m 'version 1.2'

52. tag git tag: list the tags
git tag -l ‘v1.*’ : list the tags that matches the pattern

53. Diffs
git diff: shows the difference between your working directory and the index
git diff commit_id: summarizes the differences between the working directory and the given commit
git diff --cached commit_id: show the differences between the staged changes in the index and the given commit
git diff c1 c2: displays the differences between the two given commits
git diff master feature1: shows the difference between the two specified branches

54. Diffs

55. Merges
A merge unify two or more commit history branches (one commit can have multiple parents…)

56. git merge other_branch
Merges
git merge other_branch
Working directory should be clean
Conflicts can occur

57. Conflicts
Git keeps track of problematic files by marking each one in the index as conflicted or unmerged

58. Conflicts

59. How git tracks conflicts
./git/MERGE_HEAD contains the SHA of the commit that is merging
./git/MERGE_MSG contains the default merge message used when commit to resolve the conflict
The index contains 3 copies of each conflicted file: the merge base, “our” and “their”
The conflicted version is not stored in the index

60. Resolve a conflict Adjust the file to mach the desired status
git add file
git commit –m "Resolved conflict"

61. git reset --hard [previuous_commit_id]
Aborting a merge
When in troubles
git merge --abort
If the commit is already done
git reset --hard [previuous_commit_id]
git saves the original branch HEAD in the ORIG_HEAD ref

62. Resolve a conflict Merge using other branch changes
git merge --strategy-option theirs branch_name
Merge using current changes
git merge --strategy-option ours branch_name
-X is the same of --strategy-option

63. Degenerate merges
Already up to date: when all the commits from the other branch are already present in the target branch
Fast-forward: when the current branch is already present in the other branch (other branch’s last commit is descendant of HEAD)

64. git merge —-squash other_branch
Squash merges
Sometimes is useful to squash all commits into a single commit
git merge —-squash other_branch

65. Altering history A general rule:
Feel free to alter and improve your repository commit history as long as no other developer has obtained a copy of your repository (more on this later…)

66. git reset --soft [commit_id]
The --soft changes the HEAD ref to point to the given commit. The contents of index and working directory are left unchanged
git reset --soft [commit_id]

67. git reset --mixed [commit_id]
The --mixed changes the HEAD ref to point to the given commit. The index content is modified to align with the tree structure of the given commit, but the working directory remains unchanged
This is the default option for reset

68. git reset --hard [commit_id]
The --hard changes the HEAD ref to point to the given commit. The index content and the working directory are modified to align with the tree structure of the given commit.

69. git reset
In practice:
reset moves the current branch HEAD within the commit graph to a specific commit. If --hard is specified the working directory is transformed as well.

70. git reset Option HEAD Index Working directory --soft Y N --mixed
--hard

71. git cherry-pick commit
Applies the changes introduced by a commit on the current branch
It will introduce a new commit adding it to the history
git cherry-pick commit

72. git revert It applies the inverse of the given commit
git revert commit

73. amend Sometimes happens to forgot a file or to correct a typo
It doesn’t create a new commit but change the last one (altering history!!!)
git commit --amend

74. rebase The normal merge command “soil” the current branch
rebase is a sort of cleaner merge
forward-port local commits to the updated upstream head

75. rebase master topic git checkout topic git rebase master A B C D E W XY Z
topic
git checkout topic git rebase master

76. rebase A B C D E
master W’ X’ Y’ Z’
topic

77. git add something something_else git rebase --continue
If conflict is found the rebase operation suspend its process temporarily so that the conflict can be resolved
continue with
git add something something_else git rebase --continue

78. rebase (interactively)
Can be used to squash or modify commits
git rebase -i master~3

79. rebase -i

80. The Stash git stash [save]
Is a mechanism for capturing your work in progress allowing to save it and return to it later
Save and clear any modification
Save the snapshot in a stack
git stash [save]
Something like a commit… without a commit! :-)

81. git stash branch new_branch
The Stash
git stash pop
Extract and remove the snapshot from the stash and apply it to the current branch
git stash apply
Apply the snapshot to the current branch without removing it from the stash
git stash branch new_branch
Apply the snapshot creating a new branch
Apply the snapshot to the current branch without removing it from the stash

82. git stash drop [snapshot_id]
The Stash
git stash list
List available snapshots
git stash drop [snapshot_id]
Remove given (default: last) snapshot
Apply the snapshot to the current branch without removing it from the stash

83. remote repositories By now everything was local
Git is a DVCS (D - Distributed)
A remote is a reference to another repository through a network
A clone is a copy of a repository: it contains all the objects from the original.

84. git clone url_to_a_repository
It copies all the objects from the remote repo into a local repository
It maintains a link to the original via a remote called origin
The remote repo doesn’t know anything about its clones

85. remote The git remote command is useful to manage the remotes
add, rm , show
Multiple remotes can exist:
central repo
production
test

86. fetch, pull and push
fetch retrieves objects and related metadata from a remote repository
pull like fetch plus merge changes into a corresponding local branch
push transfer local objects and metadata to a remote repository

87. git push [-u] origin branch_name
fetch, pull and push
Used to sync with remote repositories (usually the central repository)
Flow:
Work locally
Push commits to the remotes
git push [-u] origin branch_name

88. Submodules
It’s a tool to import in the current repository dependencies or other libraries that are useful for the project (SVN Externals)

89. submodule git submodule add /path/to/repo sub_name
It clones the repo and create a .gitmodule file with module information
[submodule "rack"]
path = rack
url = git://github.com/chneukirchen/rack.git

90. submodule
When a repo with submodule is cloned two additional commands must be issued:
git submodule init
git submodule update

91. Daily use Different branch for environment/customer Branch per feature
Tags for version

92. Gitflow

93. GUIs Don’t underestimate the power of the command line
But sometimes GUIs are better (especially for diff and log)
VS2015/2017 has the git plugin

95. https://windows.github.com/

96. some useful commands Permanently remove a file from the history:
git filter-branch --tree-filter 'rm -rf file_to_delete’ HEAD

97. some useful commands Delete a remote branch
git push origin :nome_del_branch
git push –-delete origin nome_del_branch

98. some useful commands Push from one branch to another
git push <remote> <local_branch_name>:<remote_branch_to_push_into >

99. some useful commands Sync the local branch list with remote
git remote prune origin

100. some useful commands list the most touched files
git log --pretty=format: --name-only | sort | uniq -c | sort -rg | head -10

101. some useful commands Show a file on a specific branch
git show feature1:file1.txt

102. The end