Version Control

Michael L. Collard, Ph.D.

Department of Computer Science, The University of Akron


  • Software Configuration Management
  • Tracking and controlling changes to files used in software development
  • Based on revision control (version control)
  • Used for managing builds and releases
  • Used for accounting and auditing of process and product

We use version control for …

  • Coordinating source code for a particular release
  • Collecting metrics on software productivity
  • Studying the process of development
  • Informing non-developers of the current state of the source code
  • Bringing new and absent developers up to date

diff and patch

  • Distribute changes efficiently
  • Simplistic form of handling versions
  • diff utility creates a patch file
  • The patch utility applies the patch file to the starting code to create the updated file

Ex: Create a Patch

Ex: Apply a Patch

Revision Control (Version Control)

  • After an editor and a compiler, the most crucial tool for software development
  • Essential to the coordination of changes among collaborating developers
  • Essential to a solitary developer working on anything non-trivial
  • Maintains a history of changes
  • Management of branches and product families
  • Defines workflow
  • All parts of development revolve around version control

Common Features

  • Versioning down to file level
  • Text Files: Only understands the lexical level (i.e., a source-code file is a file of characters)
    • No understanding of the syntactic structure of code
  • Binary Files: Stays at the file level

Management Models

  • File Locking
  • Original
  • Primarily not used for source code anymore
  • Version Merging
  • More recent
  • What developers use for source code

Management Model: File Locking

  • Only one developer at a time has access to a file/resource
  • Lock-Modify-Unlock
  • One developer at a time has the "token"; other developers have to wait
  • Library model
  • Advantage: No merging problems
  • Disadvantage: Prevents other developers from working
  • Disadvantage: Impractical in distributed development due to time/space differences

Management Model: Version Merging

  • No restrictions on access
  • Developers can work simultaneously
  • Copy-Modify-Merge
  • Advantage: No restrictions on working
  • Disadvantage: Merge issues

Current Practice

  • A large majority of the usage of version control is Version Merging
  • File Locking is typically only used for binary files (e.g., MS Word files)
  • May find old projects (and developers) that use File Locking

Centralized Version Control

  • e.g., Subversion (SVN), ClearCase, Vault
  • A single central repository, local working copies
  • Access controlled by the server
  • One sequence of version numbers
  • Traditional approach

SVN View

  • (remote) repository:
  • The single, central SVN repository typically running on a remote machine
  • working copy:
  • Sometimes referred to as a local repository, but it is not
  • The code you checked out into your filesystem
  • Where you modify your files


  • Versions identified by monotonically increasing numbers
  • URLs identify both the location of a central repository and directories/files in the central repository
  • Each commit has an author
  • Support for per-directory permissions, with some limitations

SVN Workflow

  • Update the working copy
  • Perform changes in a local repository ("working copy")
  • Commit changes

Common SVN Issues

  • Need access to a server to create a shared repository
  • No distinction between private and public changes
  • Merging is difficult
  • Branching creates problems

Distributed Version Control

  • e.g., Git, Bazaar, Darcs, Mercurial, Monotone, SVK
  • Peer-to-peer, no central repository; all are repository copies
  • No one sequence of version "numbers" (Why?)
  • Access controlled by the server


  • Distributed revision control and SCM (Source Code Management) system
  • Created in 2005 by Linus Torvalds for Linux kernel development
  • Used by major companies, e.g., Microsoft, Apple
  • Built-in to many IDEs
  • Fluency in Git is a requirement for anybody in software engineering

Git View

  • repository
  • Stored in the (hidden) directory .git
  • What you clone from another repository

  • working copy
  • The code you checkout into your filesystem
  • The files that you see
  • Where you modify the file

Git Characteristics

  • Each commit has a hash, currently a SHA1 id (160-bit numbers in hexadecimal), e.g.,
    • dd2cfbe16889f213f33d61b594a2088e97c99856
  • URL only identifies the location of the repository. Always have branches and tags, where the default branch is the "main" (previously "master").
  • Each commit has an author and a committer

Git Characteristics

  • peer-to-peer
  • Each copy is a full-fledged repository and can be worked on locally without access to a central server
  • Each user clones the repository, makes changes, and pushes the changes

Git Benefits

  • Records complete new version
  • Handles local and remote repositories
  • Tracks merged data
  • Staging changes

Git Comparison

  • Advantages: fast, flexible, powerful, multiuser
  • Disadvantages: complex, challenging to learn, GUI tools less developed than SVN tools
  • Despite disadvantages, Git is a standard tool for software engineering and software development in general
  • Also used as a data format for applications


  • One issue with Git is that to collaborate with others, your repository must be public
  • GitHub is a hosting service for software development projects using Git
  • Web-based hosting site for Git repositories
  • > 372 million repositories with ~28 million public repos, > 100 million users
  • Founded in 2008, Microsoft purchased in 2018
  • An account at GitHub is necessary for software development and software engineering (not just this class)

Git Influence

  • Microsoft:
  • Visual Studio Online 2015
  • Visual Studio 2019: New Git Experience
  • Azure Repos
  • Apple:
  • Current: XCode 13 and macOS Big Sur 11
  • XCode - Git/SVN support through XCode 8
  • XCode 9: Dropped SVN support
  • XCode 11: SVN deprecated
  • macOS Catalina 10.15: No longer installed on the command line
  • This is not a criticism of using SVN for CS 1 and CSII

Git Tools

  • Command-line git.
  • GUI Tools
  • Note: Apple XCode

Recommendation: command-line Git

  • Command-line git is the proper Git; everything else is an approximation
  • Most answers to Git questions show the command line answer
  • As you use the command line, you start to remember commands (not the case in GUIs)
  • Often, the GUI "easy" solutions are not the only way to fix a problem and are often not the best
  • GUIs overlay proper git and try to make it simpler, but they fail
  • Can script/automate command-line solutions


  • Linux - Command-line git
  • macOS - Command-line git
  • Windows - Git Bash in Git for Windows

SVN/Git Command Comparison

svn checkout url git clone url
svn update git pull
svn commit -m "Add feature" git commit -am "Add feature"; git push
svn status git status
svn revert path git reset –hard path
svn add file; svn rm file; svn mv file git add file; git rm file; git mv file