Version Control

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# Version Control
## The evolution of GIT...

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## In the beginning...

* Sneakernet
* Here hold my tape drive

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## Historically

* Source Code Control System
 * 1972 - 2006
 * Bell Labs
 * Interleaved deltas
 * Good for text, bad for binary
* Revision Control System
 * 1982 - ?
 * diff utility based

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## Historically

* Concurrent Versions System (CVS)
 * 1986 - 2008
 * Series of scripts originally using RCS
 * Takes a lot of flack for newer design philosophy changes
* Subversion (SVN)
 * 2000 - ?
 * rename issue

.center[![Version Control](https://miro.medium.com/max/400/1*9yJY7fyscWFUVRqnx0BM6A.png)]
.footnote[.red.bold[*] [Image Source](https://medium.com/devsondevs/gitflow-workflow-continuous-integration-continuous-delivery-7f4643abb64f)]

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## What changed?

* Distributed vs Centralized
 * peer to peer
 * working copies
 * communicate only when sharing changes
 * multiple backups
* Proprietary Systems
 * use license changed

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## GIT

* 2005 - ?
 * Linus Torvalds
* full working directory
* used for the linux kernel for patching
* safeguards corruption (accidental or malicious)
* multiple merge strategies
 * resolve, recursive, octopus
* data structures
 * blob, tree (directory), commit (links tree objects into history), tag (container of metadata and reference of another object)

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## GIT Concepts and Practices

* commit early and often
* copy/move a file in a different commit from any file changes
* name your stashes
 * git stash save (name)
* don’t commit anything that can be regenerated from other things that were committed

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## GIT Commands

* checkout
 * git clone ssh://user@host/path/to/repo.git
  * creates shortcut called origin
* status
 * git status
* adding
 * git add <filename/>
* commit changes (local)
 * git commit

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## GIT Commands

* commit changes (remote)
 * git push origin master
  * origin - remote connection to the central repo
  * master - branch
* pull updates (conflicts)
 * git pull --rebase origin master
* resolve conflicts
 * git rebase --continue
  * don’t panic
   * git rebase --abort
 * git push origin master

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## GIT Commands

* Stashing
 * Saving your work without commit
 * git stash 
 * git stash list
 * git stash apply
  * apply the previous stash to current
* branches
 * git branch <branchname/>
 * git checkout <branchname/>
* merging branches
 * git checkout master
 * git merge <branchname/>

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## GIT Maintenance

* git log
 * see pointers and other information
* git fsck
 * Validates git repo
* git gc
 * Removes dangling objects
 
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## GIT example
```bash
git checkout -b proj-404
git status
git add newclass.py
# code changes
git commit
# rinse and repeat
git push -u origin proj-404
# code changes
git push
# code changes
```
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## GIT example
```bash
git checkout master
# checkout master branch
git pull
# pull changes
git pull origin proj-404
# pull changes on this branch
git push
# pushes changes back to origin master
```
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## Resources

* https://git-scm.com/doc
* https://en.wikipedia.org/wiki/Merge_%28version_control%29#Three-way_merge
* https://sethrobertson.github.io/GitBestPractices/
* https://git-scm.com/book/en/v1/Git-Tools-Stashing
* https://git-scm.com/book/en/v2/Git-Branching-Basic-Branching-and-Merging

## Workflows

* http://reinh.com/blog/2009/03/02/a-git-workflow-for-agile-teams.html
* https://www.atlassian.com/git/tutorials/comparing-workflows/centralized-workflow