LESSON 1: Fundamental Operations with Git

LESSON 1: Fundamental Operations with Git#

Lecture notes on the fundamental operations with Git. A hands-on lesson for introducing version control, tracking changes, and the tracking history.

Learning Objectives:

  • To understand the basic operations of version control using Git.

  • To use Git to create repositories and commit changes.

  • To apply Git operations to track, reverse and delete changes in working documents.

  • To organise tracked changes in the Git history.

Topics:

git syntax version control repositories tracking changes untracking files gitignore undoing changes deleting and renaming files committing changes inspecting changes tags

Materials:

Preparation#

Instructor’s Note

  • The instructor must deliver the lesson in an environment containing the latest stable version of Git. Participants should also have the latest version of Git installed on their machines.

  • The instructor must remove any custom configurations from the environment (i.e., Git and the shell terminal). Personal configuation may interfere with the lesson.

  • Adjust the code examples in this lesson to reflect any changes intruduced in the latest version of Git.

Episode 1: Git repositories for version control#

ca 50 min total

1.1.0 Welcome slides#

10 min

Introduce:

  • Trainers

  • Code of conduct

  • Course outline

  • Today’s schedule

  • The need for and goals of version control

  • The role of git as a software solution supporting these goals

1.1.1 Introduction to Git#

10 min

  • Create a directory for the course

Instructor’s Note

Students are assumed to have at least basic awareness of working from the command line and navigating the directory tree, but help them if necessary.

In the first section, we create the directory that will house the project. Note that depending on the environment setup, the Desktop may or may not actually be under the participants’ home directory so instructor and helpers should be ready to help learners locate it.

    cd ~/Desktop/
    ls
    mkdir -p 2410-gitcodev/git
    ls
    ls 2410-gitcodev/

    cd 2410-gitcodev/git/
    ls
    pwd

  • Check which shell is available

    echo $SHELL
    echo

  • Check installed version of Git

  • (This will be the participants’ first interaction with git, so any installation or PATH problems should show up here)

    git
    git --version
    git version

1.1.2 Git Command Syntax and Getting Help#

10 min

  • We indtoduce the git help system both as a resource that they can use in future, and a way to start getting used to the CLI interface and command format.

    git help
    git help help
    git config
    git config --list

Introduce the key config parameterts, including pre-setting some that only apply on day 2. Participants may need a reminder to substitute their own details, and a quick explanation of the Windiws vs Unix end-of-line conventions (Carriage Return / Linefeed on Windows, only Linefeed on Mac / Linux / other unixoids)

    git config --global user.name "John Doe"
    git config --global user.email johndoe@example.com
    git config --global core.editor nano
    git config --global core.autocrlf input # false for Win
    git config --global init.defaultBranch main
    git config --list
    git help config

    git help glossary
    git help -g

1.1.3. Creating an Empty Reposiory#

10 min

Instructor’s Note

Here and throughout, it is possible to edit the file with an editor rather than appending lines with echo, however this will make the nature of the changes invisible in any gitautopush record, so is not recommended in class.

  • We add some content to a file and observe that, where no repo has been initialised, operations like ‘git status’ don’t do very much.

  • We follow this with a git init. It is important to be sure that all participants are actuall in the correct directory when they do this.

    pwd
    ls
    echo 'first line'
    echo 'first line' >lines.txt
    ls

    cat lines.txt
    echo 'second line' >>lines.txt
    cat lines.txt 
    git status
    git init

The git status command above should return a fatal error because we are not in a repository.

    ls
    ls -a
    ls -aF
    ls -aF .git
    ls

1.1.4. Q&A#

10 min

At this point, we have an empty repository, plus a single file in a working directory that has not been added to the repository. Students have had a brief view (via ls -af .git) of the inner contents of the repository proper, but should not be encouraged to dig too deeply at this point.

Episode 2: Tracking Changes in Working Documents#

ca 75 min

1.2.1 Tracking Changes with the Index#

10 min

  • In this section, we observe that a file in the working directory that has not been explicitly added to the repo is observed by git status, but not yet tracked. So we introduce the git add command and, alongside it, git diff.

    git status 
    git add lines.txt
    git status 
    ls -a .git
    git diff lines.txt

Instructor’s Note

The only visible difference between the output of this and the previous ls -a .git is the appearance of the index

    echo 'third line' >>lines.txt
    cat lines.txt
    git diff lines.txt

Output: The output of the git diff command should resemble the following. Use this opportunity to explore the format of a diff file.

    diff --git a/lines.txt b/lines.txt
    index 06fcdd7..20aeba2 100644
    --- a/lines.txt
    +++ b/lines.txt
    @@ -1,2 +1,3 @@
     first line
     second line
    +third line

  • We see that new additions to tracked file still need to be added to the index. The instructor may want to explain cases where this is relevant and useful.

    git status 
    git add lines.txt
    git status 
    git diff lines.txt

Exercise 1.1 — Tracking changes with the Index

Tracking changes with the index

5 min

Please perform the following tasks alone

The current file lines.txt contains three lines

  1. Revise in your terminal the commands we have used so far

    1. Append to the file a fourth line (in the same style as the previous lines)

    2. Check the new content of the file using…

    3. Check whether Git realises that a change has occurred using…

    4. Check which difference Git finds in the file using… Take note of the output of the Git commands

  2. Follow the action that Git suggests next by using…

    1. Same as 1.2

    2. Same as 1.3

    3. Same as 1.4

Take note of how the outputs of Git commands have changed

Formulate your own explanation of what you have observed The following questions are two sides of the same coin:

  • What did you ask Git to do?

  • What did Git do for you?

Answers
[No answers yet]

Tracking Directories#

10 min

Instructor’s Note

In this section, we see that while empty directories are not tracked or `seen’ by git, adding a directory to the index automatically adds its contents.

    mkdir directory
    ls
    ls -F
    git status 
    touch directory/emptyfile.txt

  • git status should not ‘notice’ the empty directory

    ls -R
    ls -RF
    git status 
    git status -u
    git help status

  • git status should report the untracked filename

    git add directory
    git status

  • git status here should report emptyfile.txt as staged but not committed

1.2.2 Not Tracking and Stop Tracking#

10 min

Instructor’s Note

In this section, we introduce the .gitignore mechanism. It is worth taking a few minutes to talk about the kinds of files associated with a project that you might not want to track, such as IDE configurations, Apple .DS_Store files, log files, test run outputs etc. We don’t want these cluttering up our git status output, or accidentally messing up our coleagues’ work environments.

  • First, we generate a random log file of the kind we don’t want to track.

    history
    history 20
    history 20 >history.log
    cat history.log 
    git status

  • git status reports the new, untracked file

  • Next, we will add a glob that matches the file to .gitignore.

    echo '*.log'
    echo '*.log' >.gitignore
    git status
    ls -a
    ls -aF

  • git status should no longer report the file at all, although it is still present in the working directory

    git add .gitignore
    git status 
    echo 'lines.txt' >>.gitignore
    cat .gitignore

Instructor’s Note

Adding lines.txt, as we can see in the git status output, does not remove lines.txt from the index, and git continues to track it, but would not start tracking it or offer it for staging if it were new.

    git status 
    git add .gitignore 
    git status

  • .gitignore is a regular file and will be tracked unless listed in .gitignore. Whether or not this is a good idea for a particular project is up to the collaborators.

Ignore Untracked Directories#

10 min

Instructor’s Note

This section illustrates three points:

  • That git ignores the contents of directories that match a line in .gitignore,

  • That ! is a not operatory for matching purposes

  • That git will implement the ‘last rule standing’ after parsing .gitignore

    touch directory/trackme.txt
    touch directory/donttrackme.txt
    ls directory/
    git status 
    echo 'directory' >> .gitignore

    cat .gitignore 
    git status
    echo '!directory' >> .gitignore
    cat .gitignore 
    git status

    cat .gitignore 
    echo 'directory' >>.gitignore
    cat .gitignore 
    git status 
    git help gitignore

    git status 
    git add .gitignore 
    git status 

    git rm --cached directory/emptyfile.txt 
    git status 
    ls -FR

Exercise 1.2 — Stop tracking Changes in a File

Stop tracking changes in a file

5 min

Please perform the following tasks individually

  1. Revise the commands we have used since the last exercise. Could you use a shell command for this?

  2. Ask Git for the current state of the repository using…

  3. Stop tracking the file directory/emptyfile.txt

    Caution

    Be mindful of not deleting the file!

  4. Verify the result of your action using…

Formulate your own explanation of what you have observed The following questions are two sides of the same coin:

  • What did you ask Git to do?

  • What did Git do for you?

Answers
[No answers yet]

1.2.3 Undoing Changes with the Index#

10 min

Instructor’s Note

The central idea here is the use of git restore to ‘undo’ changes to tracked files in the working directory from the index, not from the commit history, as we haven’t introduced that yet.

    cat lines.txt 
    echo 'fifth line' >>lines.txt 
    cat lines.txt 
    git status 
    git diff lines.txt

    git restore lines.txt
    cat lines.txt 
    git status 
    git diff lines.txt
    git restore lines.txt

    cat lines.txt 
    git status 
    echo '!directory' >>.gitignore
    ls
    git status 

    git status -u
    git add directory/trackme.txt 
    git status -u
    git add directory/donttrackme.txt 
    git add directory/emptyfile.txt

    git status 
    git add .gitignore 
    git status

1.2.4 Deleting and renaming tracked files and directories#

10 min

Instructor’s Note

Here we illustrate the need to use git’s utilities to delete or rename files that are tracked in the repo, if their history is to be properly maintained.

    git rm --cached directory/donttrackme.txt 
    git status 
    rm -r directory/
    ls -FR

    git status 
    git restore directory
    git status 
    ls -FR directory/
    touch directory/donttrackme.txt

    git status 
    git rm directory
    git rm -r directory
    git status 
    git rm -rf directory

    git status 
    ls -FR directory/
    git restore directory
    git status 
    git status -u

    mv directory/donttrackme.txt directory/trackne.txt
    git status -u
    # use the command `git mv <oldname> <newname>`
    # lines.txt Lines.txt
    git status -u
    git mv lines.txt Lines.txt
    git status -u

Exercise 1.3 — Renaming Tracked Files

Renaming tracked files

5 min

Please perform the following tasks individually

  1. Revise the commands we have used since the last exercise. Could you use a shell command for this?

  2. Ask Git for the current state of the repository using…

  3. Rename the file lines.txt as Lines.txt using…

  4. Verify that the working tree contains Lines.txt using…

  5. Verify that Git tracks Lines.txt using…

Answers
[No answers yet]

Episode 3: Organizing Tracked Changes in a History#

ca 75 min

Instructor’s Note

This is a critical moment in the lesson. We have introduced the index, as a representation of the project at a point in time. Now we begin to develop the idea of the repository as a sequence of such staged changes over time that culminate in the current state of the project (or branch, but we haven’t introduced that concept yet), HEAD.

1.3.1 Commiting Changes with a Configured Identify and a Message#

10 min

  • We introduce the ‘git commit’ command as an commitment of the state of the index at some point in time.

  • We note that a commit MUST be accompanied by a descriptive message

    cat Lines.txt 
    git diff
    git status 
    git commit -m 'Add first four lines' Lines.txt

  • We see next that a succesful commit gives us a ‘clean’ index with no stages changes, but we can look at a log and see the history.

  • When we look at the log, we see the ‘long form’ commit ID for the commit we just made, which is effectively guaranteed to be globally unique.

    git status 
    git log

Exercise 1.4 — Commit Changes in a Tracked File

Commit changes in a tracked file

5 min

Please perform the following tasks individually

Check if .gitignore is ready to be committed using… Commit .gitignore using…

Attention

DO NOT forget the commit message describing your action

Answers
    git status 
    git commit -m 'Add .gitignore' .gitignore 
    git status 

    rm -r directory  # to keep things clean
    git status 
    ls
    git log

Exercise 1.5 — Follow the state of the repository in the commit routine

Follow the state of the repository in the commit routine

5 min

Please perform the following tasks individually.

  1. The baseline

    1. Revise the commands launched since the last exercise using…

    2. Check the output of git status

  2. The working tree

    1. Append the fifth line to Lines.txt using…

    2. Repeat 1.2 and compare its output with the previous

  3. The index

    1. Stage the changes of Lines.txt in the index using…

    2. Repeat 1.2 and compare its output with the previous ones

  4. The history

    1. Store the changes of Lines.txt in the history using…

    2. Repeat 1.2 and compare its output with the previous ones

    3. Look up and parse the commit history using…

Formulate your own explanation of what git status showed you The following questions are two sides of the same coin:

  • What did you ask Git to do?

  • What did Git do for you?

Answers
    # Procedure for exercise 5
    echo 'fifth line' >>Lines.txt 
    cat Lines.txt 
    git status 
    git add Lines.txt 
    git status

    git commit -m 'Add fifth lines' Lines.txt 
    git status 
    history
    git log

1.3.2 Inspecting Changes Using the History#

Exercise 1.6 — Follow the state of the index in the commit routines

Follow the state of the index in the commit routine

5 min

Please perform the following tasks individually

  1. The baseline

    1. Revise the commands launched since the last exercise using…

    2. Check the output of git diff

  2. The working tree

    1. Append the sixth line to Lines.txt using…

    2. Repeat 1.2 and compare its output with the previous

  3. The index

    1. Stage the changes of Lines.txt in the index using…

    2. Repeat 1.2 and compare its output with the previous ones

  4. The history

    1. Store the changes of Lines.txt in the history using…

    2. Repeat 1.2 and compare its output with the previous ones

    3. Look up and parse the commit history using…

Formulate your own explanation of what git diff showed you The following questions are two sides of the same coin:

  • What did you ask Git to do?

  • What did Git do for you?

Answers
    # procedure for exercise 6
    git status 
    git diff
    echo 'sixth line' >>Lines.txt 
    git diff
    git add Lines.txt

    git diff
    git diff Lines.txt
    git commit -m 'Add sixth line' Lines.txt 
    git diff
    git log

    git log --oneline
    git status 
    echo 'seventh line' >>Lines.txt 
    git diff Lines.txt
    git add Lines.txt

    git diff Lines.txt
    git status 
    git log --oneline
    git diff HEAD Lines.txt
    git diff e278702 Lines.txt

    git diff HEAD~1 Lines.txt
    git log --oneline
    git diff 7f2ca Lines.txt
    git diff HEAD~2 Lines.txt
    git diff HEAD~3 Lines.txt

    git diff HEAD~7 Lines.txt
    git diff Lines.txt
    git diff HEAD~3 Lines.txt
    git diff HEAD HEAD~1 Lines.txt
    git diff HEAD~1 HEAD Lines.txt

    git diff HEAD~4 HEAD~2 Lines.txt
    git diff HEAD~3 HEAD~2 Lines.txt
    git log
    # 
    pwd

    git status 
    git log --oneline
    git diff Lines.txt
    git diff HEAD Lines.txt
    git diff HEAD~1 Lines.txt

    git diff HEAD HEAD~1 Lines.txt
    git diff HEAD~1 HEAD Lines.txt
    diff HEAD HEAD Lines.txt 
    git diff HEAD HEAD Lines.txt 
    git diff HEAD~2 HEAD~2 Lines.txt

Break#

10 min

Exercise 1.7 — Explore the changes recorded in the history

Explore the changes recorded in the history

7 min

Please perform the following tasks individually

  1. The baseline

    1. Revise the commands launched since the last exercise using…

  2. Perform the commit routine

    1. Append the seventh line to Lines.txt using…

    2. Stage the changes of Lines.txt in the index using…

    3. Store the changes of Lines.txt in the history using…

  3. As many times as you like

    1. Check the history using…

    2. Compare different versions of Lines.txt using…

Formulate your own explanation of what you have observed The following questions are two sides of the same coin:

  • What did you ask Git to do?

  • What did Git do for you?

Attention

Are there shortcuts to do the same with less typing?

Answers
    # No answers yet

Exercise 8 is an optional exercise about comparing differences in the history.

1.3.3 Undoing Changes with the History#

10 min

Instructor’s Note

This topic involves using git restore. We have introduced the HEAD~x notation in the exercises above, and we will introduce both the short form commit ID and the tag mechanism shortly. Here we see that using the -s flag we can specify a source (commit) from which to restore a specified file.

    git restore -s HEAD~2 Lines.txt
    cat Lines.txt
    git status
    git restore -s HEAD Lines.txt
    git status

1.3.4 Marking the History Using Tags#

10 min

  • Lightweight tags

  • Using the git tag mechanism, we can ‘name’specified commits for ease of reference. These may represent special points in a project, like releases, or particular points in the development lifecycle, or just be useful ‘bookmarks’.

  • We also see here, using git log –oneline, the short form commit ID, which is effectively guaranteed to be project-unique, if not globally unique.

    git log --oneline
    git tag 'hey'
    git log --oneline
    git log

    git tag 'hey' HEAD~1
    git tag 'hey2' HEAD~1
    git log --oneline
    git tag 'hey3' HEAD~5
    git tag 'hey4' 87ab7b6

    git log --oneline
    git diff HEAD HEAD~1 Line.txt
    git diff HEAD HEAD~1 Lines.txt
    git diff hey hey2 Lines.txt
    git log --oneline

    git diff hey hey2 Lines.txt
    echo 'eighth line' >>Lines.txt
    cat Lines.txt 
    git status 
    git add Lines.txt

    git status 
    git commit -m 'Add eighth line' Lines.txt
    git log --oneline
    git tag -d hey1
    git tag -d hey4

    git log --oneline
    git diff hey hey4 Lines.txt
    git log --oneline
    git tag -d hey2
    git tag -d hey

    git tag HEAD~4 v1
    git tag v1 HEAD~4
    git log --oneline
    git tag v2 HEAD~3
    git tag v3 HEAD~2

    git log --onelein
    git log --oneline
    git tag v4 HEAD~1
    git tag v5 HEAD
    git log --oneline

Exercise 1.9 — Add lightweight tags to the history

Add lightweight tags to the history

5 min

Please perform the following tasks individually

Two commits come from exercises (as opposed to instructor-led typing)

  1. Find out which commits they where

  2. Tag them as exercises using… Use capital letters for the tag name (for our convenience)

  3. Verify the outcome of tagging with two Git commands, namely … and …

Formulate your own explanation of what you have observed

The following questions are two sides of the same coin:

  • What did you ask Git to do?

  • What did Git do for you?

Answers
    # no answers yet

  • Annotated Tags

  • THis section is fundamentally similar except that the tags get an additional annotation via the -m option.

    git tag -a
    git tag -a -m 'First annotated tag' 
    git tag -a -m 'First annotated tag' TAG1
    git log --oneline

    git tag
    git show
    git show HEAD~1
    true

Lesson Summary#

10 min

Give a short wrap up about what has been learned. Encourage questions and perhaps give a ‘teaser trailer’ for lesson 2.

Instructor’s Note

Remember to coordinate with the trainer for day 2 to ensure that they have a repository that begins day 2 with the same state as the learners, either by their rerunning the command log, or by physically copying your repo in a ZIP or tarfile.

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