How to Backtrack- Learn different ways to undo changes made to a Git project and when to use them.

• Head commit:

In Git, the commit you are currently on is known as the HEADcommit. In many cases, the most recently made commit is theHEAD commit.

To see the HEAD commit, enter:

git show HEAD

The output of this command will display everything the git log command displays for the HEAD commit, plus all the file changes that were committed.

For example: Enter the command to show the HEAD commit.

Notice the output. The ghost's most recently added line is in green text.

• Git Checkout:

What if you decide to change the ghost's line in the working directory, but then decide you wanted to discard that change?

You could rewrite the line how it was originally, but what if you forgot the exact wording? The command

git checkout HEAD filename

will restore the file in your working directory to look exactly as it did when you last made a commit.

1. Make changes as you want on your coding/comment.

2. From the terminal, use git diff to see the difference between file_name as it appears in the working directory vs. how it appears in your last commit.

You may need to press q on your keyboard to restore the terminal.

3. Use the new Git command  (git checkout HEAD filename) to restore the file in your working directory to look as it did when you last made a commit.

Notice that the changes you made to the ghost's line have been discarded.

• In Git, it's common to change many files, add those files to the staging area, and commit them to Git in a single commit.

For example, say you want to change the character "LARRY" to "LAERTES" in the script. The name currently appears in two files. After you change the name in both files, you could add the changed files to the staging area with:

git add filename_1 filename_2

Note the word filename above refers to the name of the file you are adding to the staging area.

• Git Reset:

What if, before you commit, you accidentally delete an important line from file_1.txt (for example)? Unthinkingly, you add file_1.txt to the staging area. The file change is unrelated to the previous step's swap (change) and you don't want to include it in the commit.

We can unstage that file from the staging area using

git reset HEAD filename

This command resets the file in the staging area to be the same as the HEAD commit. It does not discard file changes from the working directory, it just removes them from the staging area.

Test steps:

1. Make changes into file_1.txt file.

2. Add the above file to the Git staging area.

3. Now check the status of the Git project.

In the output, notice file_1.txt under “Changes to be committed”.

4. Use the new Git command (git reset HEAD filename) to unstage file_1.txt from the staging area.

Notice in the test output, "Unstaged changes after reset":

M    scene-2.txt

• M is short for "modification"

5. Now that changes made to file_1.txt have been booted out of the staging area, you're ready to commit. Make a commit to save the previous swap in Project.

• Creating a project is like hiking in a dark forest. Sometimes you take a wrong turn, then another wrong turn. Before you know it, you're surrounded by bears.

Git enables you to rewind to the part before you made the wrong turn and create a new destiny for the project. You can do this with:

git reset SHA

This command works by using the first 7 characters of the SHA of a previous commit. For example, if the SHA of the previous commit is5d692065cf51a2f50ea8e7b19b5a7ae512f633ba, use:

git reset 5d69206

Test Steps:

1.  Print out your Git commit log.

2. From the terminal, enter the command to reset to a previous commit, using the first 7 characters of one of the past commit SHAs in your Git log.

Next, print the Git commit log again.

Notice anything interesting? The commits that came after the one you reset to are gone. The HEAD commit has been reassigned. You just changed history.

• Better understanding of RESET action:

To better understand git reset commit_SHA, notice the diagram above. Each circle represents a commit.

Before reset:

• HEAD is at the most recent commit

After resetting:

• HEAD goes to a previously made commit of your choice
• The gray commits are no longer part of your project
• You have in essence rewinded the project's history

• Let's take a recap:

Let's take a moment to review the new commands:

• git checkout HEAD filename: Discards changes in the working directory.
• git reset HEAD filename: Unstages file changes in the staging area.
• git reset SHA: Can be used to reset to a previous commit in your commit history.

Additionally, you learned a way to add multiple files to the staging area with a single command:

git add filename_1 filename_2