External Links
- @[https://git-scm.com/book/en/v2]
- @[https://learnxinyminutes.com/docs/git/]

See UStore: Distributed Storage with rich semantics!!!
  (Forcibly incomplete but still quite pertinent list of core people and companies)
- Linus Torvald:  
  L.T. initiated the project to fix problems with distributed
  development of the Linux Kernel.
- Junio C. Hamano:  lead git maintainer (+8700 commits)

Full Journey

Setup Server⅋Clients
- Non-normative ssh access to Git server
 ºSTEP 1:º                                 │ ºSTEP 2:º
 SSH Server                                │ remote client/s
  #!/bin/bash                              │   GIT_SSH_COMMAND="ssh "   # ← ENV.VAR To tune SSH *1
                                           │   GIT_SSH_COMMAND="$GIT_SSH_COMMAND Oº-oPort=1234º"
  if [[ $EUID != 0 ]] ; then               │   GIT_SSH_COMMAND="$GIT_SSH_COMMANDGº-i ~/.ssh/key07.keyº"
    echo "exec as root/sudo"               │   GIT_SSH_COMMAND="$GIT_SSH_COMMAND ... "
    exit 1                                 │
  fi                                       │   GIT_URL="myRemoteSSHServer"
  TEAM=team01                              │ BºGIT_URL="${GIT_URL}/var/lib/my_git_team"º
  addgroup ${TEAM}                         │ GºGIT_URL="${GIT_URL}/ourFirstProject"º
  for USER in lyarzas earizonb ; do        │                                                         
     grep "^${USER}:" /etc/passwd          │  ºgit cloneº GºmyUser1º@${GIT_URL}
     if [[ $? != 0 ]]; then                │       ^^^^^
       useradd ${USER} \                   │       create working copy of bare/non-bare repository
          --shell=/usr/bin/git-shell \     │
          --groups ${TEAM} \               │ºMake branch appear on shell prompt :º(☜strongly recomended)
          --password ${SECRET}             │(Must be done just once)
     fi                                    │ ModifyºPS1 promptº(Editing $HOME/.bashrc) to look like:
     # Add to group                        │ PS1="\h[\$(git branch 2˃/dev/null | grep ^\* | sed 's/\*/branch:/')]@\$(pwd |rev| awk -F / '{print \$1,\$2}' | rev | sed s_\ _/_) \$ "
     usermod -a -G ${TEAM} ${USER}         │          └─────────────    ºshow git branchº   ───────────────────┘   └────────────── show current and parent dir. only ────────┘
  done                                     │          $(command ...): bash syntax that executes command ...
                                           │                          and replaces standard output dynamically
BºBASE_GIT_DIR=/var/lib/${TEAM}º           │                          in PS1
GºPROJECT_NAME=project01º                  │  host1 $                           ← PROMPT BEFORE:                          
  mkdir -p ${BASE_GIT_DIR}/${PROJECT_NAME} │  host01[branch: master]@dir1/dir2  ← PROMPT AFTER:
  pushd .                                  │
  cd ${BASE_GIT_DIR}/${PROJECT_NAME} ;     │
  gitºinit --bareº                         │
  popd                                     │
  FIND="find ${BASE_GIT_DIR}"              │
  find ${BASE_GIT_DIR}         \           │
   -exec chown -R root:${TEAM} {} \;       ← Fix group
  find ${BASE_GIT_DIR} -type d \           │
   -exec chmod g+rwx {}           \;       ← Fix permissions
  find ${BASE_GIT_DIR} -type f \           │
   -exec chmod g+rw  {}           \;       ← Fix permissions 

Common flows
OºFLOW 1:º(Simplest one) no one else pushed changes before our push)
local ─→ git status ─→ git add . ─→ºgit commitº──────────────────────────────────────────────────────────→ºgit push origin featureXº
edit           ^             ^              ^                                                                     ^
               │             │              │                                                                     │
               │         add file/s         │                                                           push to remote  repository
               │         to next commit     │                                                          (ussually origin) and branch
               │                            │                                                          (featureX, master,...)      
           display changes               commit
           pending to commit             new version

OºFlow 2:ºsomeone else pushed changed before our push but there are no conflicts (each user edited different files)

local ─→ git status ─→ git add . ─→ºgit commitº─→ git pull ──────────────────────────────────────────────→ºgit push origin featureXº
edit                                               ^
                                         - git will abort and warn that changes has been pushed
                                           to remote repository+branch if we try to skip this step.
                                         - Otherwise an automatic merge is done with our local
                                           changes and any other user remote changes.

OºFlow 3:ºsomeone else pushed changed before our push, but there are  conflicts (each user edited one or more common files)

local ─→ git status ─→ git add . ─→ºgit commitº─→ git pull  ─→ "fix conflicts" ─→ git add ─→ git commit ─→ºgit push origin featureXº
edit                                                                     ^                   ^      
                                                                   │                   │      
                                                                   │             Tell git that
                                                                   │             conflicts were
                                                                   │             resolved
                                                           manually edit   
                                                           conflicting changes

OºFlow 4:ºAmend local commit
local → git status ─→ git add . ─→ºgit commitº─→ git commit ─amend ─→ ... ─→ git commit ────────────────→ºgit push origin featureXº

OºGit-Flowº Meta-Flow using widely accepted branches rules to treat with
            common issues when releasing software and managing versions
            REF: @[https://nvie.com/posts/a-successful-git-branching-model/]
 │ Standarized    │ Intended use
 │ Branch names   │                                
 │feature/...     │ merged back into main body of code
 │                │ when the developer/s are confident
 │                │ with the code quality.
 │                │ If asked to switch to another task just
 │                │ commit changes to this feature/... branch
 │                │ to continue later on.
 │develop         │ Release Staging Area:
 │                │ Merge here feature/... completed features
 │                │ NOT yet been released.
 │release         │ stable (release tagged branch)
 │hotfix branches │ branches from a tagged release.
 │                │ Fix quickly, merge to release
 │                │ and tag in release with new minor version.
 │                │ Ideally never used since our released
 │                │ software has no bugs ;D 

Change branch (checkout)
$ git checkout -b newBranch       ← alt 1, -b: creates new local branch
$ git checkout    existingBranch  ← alt 2,   : switch to existing local branch 
$ git branch -av                  ←  List (-a)ll existing branches
$ git branch -d branchToDelete    ← -d: Delete branch

$ git checkout --track "remote/branch"  ← Create  new tracking branch (TODO)

View Change History
$ git log -n 10           ← -n 10. See only 10 last commits.
$ git log -p path_to_file ← See log for file with line change details (-p: Patch applied)

$ git tag                 ← List tags
→ ...
→ v2.1.0-rc.2
→ v2.1.1
→ v2.1.2
→ ...
$ git tag -a v1.4 -m "..." ← Create annotated tag (recomended)
                                - stored as full objects in Git database.
                                - They’re checksummed; contain the tagger name,
                                - email, and date; have a tagging message (-m).
                                - can be signed and verified with GPG.

$ git tag v1.4-lw          ← Create lightweight tag
                                  - "alias" for a commit checksum stored in a file
                                  - No other info is kept.

$ git tag -a v1.2 9fceb02  ← Tag some commit in history

ºSharing Tagsº
WARN: git push command doesn’t transfer tags to remote servers. 

$ git push origin v1.5    ← Share/push tag to remote repo
$ git push origin --tags  ← Share/push all the tags
$ git tag -d v1.4-lw      ← Delete local tag (remote tags will persist)
$ git push origin --delete v1.4-lw    ← Delete remote tag. Alt 1
$ git push origin :refs/tags/v1.4-lw  ← Delete remote tag. Alt 2
                  null value before the colon is
                  being pushed to the remote tag name,
                  effectively deleting it.
$ git checkout v1.4-lw          ← Move back to (DETACHED) commit
$ git show-ref --tags    ← Map tag to commit
→ ...
→ 75509731d28ddbbb6f6cbec6e6b50aeaa413df69 refs/tags/v2.1.0-rc.2
→ 8fc0a3af313d9372fc9b8d3e5dc57b804df0588e refs/tags/v2.1.1
→ 3e1f5b0d4d081db7b40f9817c060ee7220a51633 refs/tags/v2.1.2
→ ...

Comparing diffs

- rewrite history in Git using several of the built-in filters that the command provides.   
  - rev-list command, which provides a way to list out revisions based on a range or criteria.
  - filter-branch: split a subdirectory into a separate repository
  - how to use to use filter-branch to delete a file from all versions in a repository 
    and change the email address on versions in Git history
Revert Changes
Debug Changes
REF: @[https://git-scm.com/book/en/v2/Appendix-C:-Git-Commands-Debugging]

pretty branch print

$ git log --all --decorate --oneline --graph

$ git log --graph --abbrev-commit --decorate --date=relative --all

Gitea (Gogs)
painless self-hosted Git service
- Fork of gogs, since it was unmaintained.

$ git clone --depth=1 ${URL_to_Git_repo}
            "fast clone"
            Create shallow clone with
            history truncated to the
            specified number of commits. 
            Implies --single-branch
            to clone submodules shallowly,
            use also --shallow-submodules.


$ git clone --depth=1   --branch '1.3.2'   --single-branch ${URL_to_Git_repo}
                        ^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^
                        point to branch    Clone only history
                        hash or tag        leading to the tip
                        default to HEAD)   of a single branch

Git LFS (Large Files extension)
- Git Large File Storage (LFS) replaces large files such as audio samples,
  videos, datasets, and graphics with text pointers inside Git, while storing 
  the file contents on a remote server like GitHub.com or GitHub Enterprise
4 secrets encryption tools
Encrypt Git repos
-  Git occasionally does garbage collection as part of its normal operation, 
by invoking git gc --auto. The pre-auto-gc hook is invoked just before the 
garbage collection takes place, and can be used to notify you that this is 
happening, or to abort the collection if now isn’t a good time.
- Microsoft project to enable managing massive Git 
  repositories possible. (hundreds of Gigabytes).
GPG signed
Git Hooks
Client Hooks

Client-Side Hooks
- not copied when you clone a repository
  - to enforce a policy do on the server side
- committing-workflow hooks:
    - First script to be executed.
    - used to inspect the snapshot that's about to be committed.
      - Check you’ve NOT forgotten something
      - make sure tests run
      - Exiting non-zero from this hook aborts the commit
    (can be bypassed with git commit --no-verify flag)
    - Params:
      - commit_message_path (template for final commit message)
      - type of commit
      - commit SHA-1 (if this is an amended commit)
    - run before the commit message editor is fired up 
      but after the default message is created.
    - It lets you edit the default message before the
      commit author sees it.
    - Used for non-normal-commits with auto-generated messages
      - templated commit messages
      - merge commits
      - squashed commits
      - amended commits
      - commit_message_path (written by the developer)
    - (you can easily get the last commit by running git log -1 HEAD)
    - Generally, this script is used for notification or something similar.

-ºemail-workflowº hooks:
  - invoked by ºgit amº
                Apply a series of patches from a mailbox
                prepared by git format-patch

    - Params:
      - temp_file_path containing the proposed commit message.
    - confusingly, it is run after the patch is 
      applied but before a commit is made.
    - can be used it to inspect the snapshot before making the commit,
      run tests,  inspect the working tree with this script.
    - runs after the commit is made.
    - Useful to notify a group or the author of the patch
      you pulled in that you’ve done so. 

- Others:
    - runs before you rebase anything
    - Can be used to disallow rebasing any commits
      that have already been pushed.
    - Params:
      - command_that_triggered_the_rewrite: 
        - It receives a list of rewrites on stdin.
    - run by commands that replace commits
      such as 'git commit --amend' and 'git rebase'
      (though not by git filter-branch).
    - This hook has many of the same uses as the
      post-checkout and post-merge hooks.
    - Runs after successful checkout
    - you can use it to set up your working directory
      properly for your project environment.
      This may mean moving in large binary files that 
      you don't want source controlled, auto-generating
      documentation, or something along those lines.
    - runs after a successful merge command.
    - You can use it to restore data in the working tree
      that Git can't track, such as permissions data.
      It can likewise validate the presence of files 
      external to Git control that you may want copied 
      in when the working tree changes.
    - runs during git push, after the remote refs
      have been updated but before any objects have
      been transferred.
    - It receives the name and location of the remote
      as parameters, and a list of to-be-updated refs
      through stdin.
    - You can use it to validate a set of ref updates before
      a push occurs (a non-zero exit code will abort the push).
Server-Side Hooks
(system administrator only)
- Useful to enforce nearly any kind of policy for your project.

- can exit non-zero at any time to reject the push 
  as well as print an error message back to the client; 

- you can set up a push policy that's as complex as you wish.

ºpre-receiveº hook:
 - first script to run 
 - takes a list of references that are being pushed from stdin;
   if it exits non-zero, none of them are accepted. 
 - You can use this hook to do things like make sure none of the updated 
   references are non-fast-forwards, or to do access control for all the refs 
   and files they’re modifying with the push.

 - very similar to the pre-receive script, except that 
  ºit's run once for each branch the pusher is trying to updateº.
 - If the pusher is trying to push to multiple branches, pre-receive runs only once,
   whereas update runs once per branch they're pushing to.
 - Instead of reading from stdin, this script takes three arguments:
   - the name of the reference (branch),
   - the SHA-1 that reference pointed to before the push, 
   - the SHA-1 the user is trying to push.
 - If the update script exits non-zero, only that reference is rejected; 
   other references can still be updated.

 - runs after the entire process is completed 
 - can be used to update other services or notify users.
 - It takes the same stdin data as the pre-receive hook.
 - Examples include emailing a list, notifying a CI server,
   or updating a ticket-tracking system 
   You can even parse the commit messages to see if any
   tickets need to be opened, modified, or closed.
 - This script can't stop the push process, but the client 
   doesn't disconnect until it has completed, so be careful
   if you try to do anything that may take a long time.
- TODO: how subtrees differ from submodules
- how to use the subtree to create a new project from split content
Interactive rebase
-  how to rebase functionality to alter commits in various ways.
- how to squash multiple commits down into one. 
Supporting files
- Git attributes file and how it can be used to identify binary files,
  specify line endings for file types, implement custom filters, and 
  have Git ignore specific file paths during merging.
Cregit token level blame
cregit: Token-Level Blame Information for the Linux Kernel
Blame tracks lines not tokens, cgregit blames on tokens (inside a line)
- Eclipse Distribution License - v 1.0
- lightweight, pure Java library implementing the Git version control system
  - repository access routines
  - network protocols
  - core version control algorithms

- suitable for embedding in any Java application
- git-pw requires patchwork v2.0, since it uses the 
  new REST API and other improvements, such as understanding
  the difference between patches, series and cover letters,
  to know exactly what to try and apply.

- python-based tool that integrates git and patchwork.

  $ pip install --user git-pw

  $ git config pw.server https://patchwork.kernel.org/api/1.1
  $ git config pw.token YOUR_USER_TOKEN_HERE

ºDaily work exampleº
finding and applying series
- Alternative 1: Manually
  - We could use patchwork web UI search engine for it.
    - Go to "linux-rockchip" project 
    - click on _"Show patches with" to access the filter menu.
    - filter by submitter. 

- Alternative 2: git-pw (REST API wrapper)
  - $ git-pw --project linux-rockchip series list "dynamically"
    → ID    Date         Name              Version   Submitter
    → 95139 a day ago    Add support ...   3         Gaël PORTAY
    → 93875 3 days ago   Add support ...   2         Gaël PORTAY
    → 3039  8 months ago Add support ...   1         Enric Balletbo i Serra

  - Get some more info:
    $ git-pw series show 95139
    → Property    Value
    → ID          95139
    → Date        2019-03-21T23:14:35
    → Name        Add support for drm/rockchip to dynamically control the DDR frequency.
    → URL         https://patchwork.kernel.org/project/linux-rockchip/list/?series=95139
    → Submitter   Gaël PORTAY
    → Project     Rockchip SoC list
    → Version     3
    → Received    5 of 5
    → Complete    True
    → Cover       10864561 [v3,0/5] Add support ....
    → Patches     10864575 [v3,1/5] devfreq: rockchip-dfi: Move GRF definitions to a common place.
    →     10864579 [v3,2/5] : devfreq: rk3399_dmc: Add rockchip, pmu phandle.
    →     10864589 [v3,3/5] devfreq: rk3399_dmc: Pass ODT and auto power down parameters to TF-A.
    →     10864591 [v3,4/5] arm64: dts: rk3399: Add dfi and dmc nodes.
    →     10864585 [v3,5/5] arm64: dts: rockchip: Enable dmc and dfi nodes on gru.

  - Applying the entire series (or at least trying to):
    $ git-pw series apply 95139
    fetch all the patches in the series, and apply them in the right order.
GIT Commit Standard Emojis
ºCommit type               Emoji                    Graphº
 Initial commit           :tada:                      🎉 
 Version tag              :bookmark:                  🔖 
 New feature              :sparkles:                  ✨ 
 Bugfix                   :bug:                       🐛 
 Metadata                 :card_index:                📇 
 Documentation            :books:                     📚 
 Documenting src          :bulb:                      💡 
 Performance              :racehorse:                 🐎 
 Cosmetic                 :lipstick:                  💄 
 Tests                    :rotating_light:            🚨 
 Adding a test            :white_check_mark:          ✅ 
 Make a test pass        :heavy_check_mark:           ✔️  
 General update           :zap:                       ⚡️ 
 Improve format           :art:                       🎨 
 Refactor code            :hammer:                    🔨 
 Removing stuff           :fire:                      🔥 
 CI                       :green_heart:               💚 
 Security                 :lock:                      🔒 
 Upgrading deps.         :arrow_up:                   ⬆️  
 Downgrad. deps.         :arrow_down:                 ⬇️  
 Lint                     :shirt:                     👕 
 Translation              :alien:                     👽 
 Text                     :pencil:                    📝 
 Critical hotfix          :ambulance:                 🚑 
 Deploying stuff          :rocket:                    🚀 
 Work in progress         :construction:              🚧 
 Adding CI build system   :construction_worker:       👷 
 Analytics|tracking code  :chart_with_upwards_trend:  📈 
 Removing a dependency    :heavy_minus_sign:          ➖ 
 Adding a dependency      :heavy_plus_sign:           ➕ 
 Docker                   :whale:                     🐳 
 Configuration files      :wrench:                    🔧 
 Package.json in JS       :package:                   📦 
 Merging branches         :twisted_rightwards_arrows: 🔀 
 Bad code / need improv.  :hankey:                    💩 
 Reverting changes        :rewind:                    ⏪ 
 Breaking changes         :boom:                      💥 
 Code review changes      :ok_hand:                   👌 
 Accessibility            :wheelchair:                ♿️ 
 Move/rename repository  :truck:                      🚚