• Simple formal system for tracking all changes to a project

• Time machine for your projects
  • Track blame and/or praise
  • Remove the fear of breaking things

• Learning curve is steep, but when you need it you REALLY need it

• Distributed
  • Work online or offline
  • Collaborate with large groups
• Popular and Successful
  • Active development
  • Shiny new tools and ecosystems
  • Fast
• Tracks any type of file
  • Works best with text
• Branching
  • Smarter merges

Make sure to put this information in your github profile as well.

cr173@saxon [Sta523]$ git clone https://github.com/Sta523-Fa17/DavidRobinson_TrumpTweets.git
Cloning into 'DavidRobinson_TrumpTweets'...
remote: Counting objects: 3715, done.
remote: Total 3715 (delta 0), reused 0 (delta 0), pack-reused 3715
Receiving objects: 100% (3715/3715), 199.51 MiB | 26.92 MiB/s, done.
Resolving deltas: 100% (2049/2049), done.

cr173@saxon [Sta523]$ ls
DavidRobinson_TrumpTweets
cr173@saxon [Sta523]$ ls -a DavidRobinson_TrumpTweets/
2016-08-09-trump-tweets.Rmd     DavidRobinson_TrumpTweets.Rproj trump_tweets.rda                trump_tweets_df.rda
2016-08-09-trump-tweets.html    README.md                       trump_tweets_20161128.csv

cr173@saxon [Sta523]$ cd hDavidRobinson_TrumpTweets
cr173@saxon [DavidRobinson_TrumpTweets]$ git status
On branch master
Your branch is up-to-date with 'origin/master'.
nothing to commit, working directory clean

Lets create a README.md file to include team member names and email addresses.

cr173@saxon [DavidRobinson_TrumpTweets]$ nano README.md
cr173@saxon [DavidRobinson_TrumpTweets]$ cat README.md
# DavidRobinson_TrumpTweets's Repo

## Team Members

* Colin Rundel - rundel@gmail.com

cr173@saxon [DavidRobinson_TrumpTweets]$ git status
On branch master
Your branch is up-to-date with 'origin/master'.
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:   README.md

no changes added to commit (use "git add" and/or "git commit -a")

cr173@saxon [DavidRobinson_TrumpTweets]$ git status
On branch master
Your branch is up-to-date with 'origin/master'.
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:   README.md

Untracked files:
  (use "git add <file>..." to include in what will be committed)

    TODO

no changes added to commit (use "git add" and/or "git commit -a")

• One file README.md is tracked and modified (repo is already has this file but our current version differs from the previously saved version)

• The other file TODO is untracked (this file does not exist in the repo)

Our next step is the same for both files - we want to stage our changes using git add.

cr173@saxon [DavidRobinson_TrumpTweets]$ git add README.md
cr173@saxon [DavidRobinson_TrumpTweets]$ git add TODO

cr173@saxon [DavidRobinson_TrumpTweets]$ git status
On branch master
Your branch is up-to-date with 'origin/master'.
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    modified:   README.md
    new file:   TODO

By using git add we have made git aware of the current version of both files, but we have not actually saved the changes yet.

To save the changes (locally) we need to commit them using git commit, since this change will be saved it is customary to add a message about the nature of the changes being made (for future reference).

cr173@saxon [DavidRobinson_TrumpTweets]$ git commit -m "Added Colin's information to README; Added TODO file."
[master f9c548c] Added Colin's information to README; Added TODO file.
 2 files changed, 7 insertions(+), 2 deletions(-)
 create mode 100644 TODO

cr173@saxon [DavidRobinson_TrumpTweets]$ git status
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)
nothing to commit, working directory clean

We've saved our changes but we're now out of sync with the repository on github.

What if at the same time I was making these edits my teammate John Doe was making changes to README.md on github?

github README edit

github README commit

github README status

We can attempt to send our changes back to github by using git push

cr173@saxon [DavidRobinson_TrumpTweets]$ git push
To git@github.com:Sta523-Sp17/DavidRobinson_TrumpTweets.git
 ! [rejected]        master -> master (fetch first)
error: failed to push some refs to 'git@github.com:Sta523-Sp17/DavidRobinson_TrumpTweets.git'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

cr173@saxon [DavidRobinson_TrumpTweets]$ git pull
remote: Counting objects: 3, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From github.com:Sta523-Sp17/DavidRobinson_TrumpTweets
   6b79df7..804e091  master     -> origin/master
Auto-merging README.md
CONFLICT (content): Merge conflict in README.md
Automatic merge failed; fix conflicts and then commit the result.

cr173@saxon [DavidRobinson_TrumpTweets]$ git status
On branch master
Your branch and 'origin/master' have diverged,
and have 1 and 1 different commit each, respectively.
  (use "git pull" to merge the remote branch into yours)
You have unmerged paths.
  (fix conflicts and run "git commit")

Unmerged paths:
  (use "git add <file>..." to mark resolution)

    both modified:   README.md

no changes added to commit (use "git add" and/or "git commit -a")

cr173@saxon [DavidRobinson_TrumpTweets]$ cat README.md 
DavidRobinson_TrumpTweets Repo
=======

## Team Members

<<<<<<< HEAD
* Colin Rundel - rundel@gmail.com
=======
* John Doe - j.doe@gmail.com
>>>>>>> 804e09178910383c128035ce67a58c9c1df3f558

• <<<<<<< - Indicates the start of the merge conflict.
• ======= - Indicates the break point used for comparison.
• >>>>>>> - Indicates the end of the lines that had a merge conflict.

Edit the merged file to reflect the changes you actually want.

cr173@saxon [DavidRobinson_TrumpTweets]$ nano README.md
cr173@saxon [DavidRobinson_TrumpTweets]$ cat README.md
DavidRobinson_TrumpTweets Repo
=======


## Team Members

* Colin Rundel - rundel@gmail.com
* John Doe - j.doe@gmail.com

cr173@saxon [DavidRobinson_TrumpTweets]$ git add README.md 
retBook-2:DavidRobinson_TrumpTweets rundel$ git status
On branch master
Your branch and 'origin/master' have diverged,
and have 1 and 1 different commit each, respectively.
  (use "git pull" to merge the remote branch into yours)
All conflicts fixed but you are still merging.
  (use "git commit" to conclude merge)

Changes to be committed:

    modified:   README.md

$ git commit -m "Fix Merge conflict"

cr173@saxon [DavidRobinson_TrumpTweets]$ git status
On branch master
Your branch is ahead of 'origin/master' by 2 commits.
  (use "git push" to publish your local commits)
nothing to commit, working directory clean
cr173@saxon [DavidRobinson_TrumpTweets]$ git push
Counting objects: 7, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (6/6), done.
Writing objects: 100% (7/7), 791 bytes | 0 bytes/s, done.
Total 7 (delta 1), reused 0 (delta 0)
To git@github.com:Sta523-Sp17/DavidRobinson_TrumpTweets.git
   804e091..9c4a5e7  master -> master

Above materials are derived in part from the following sources:

• Karl Broman - Wisc's Tools4RR
• Software Carpentry Project