Exercise5-HistoryAndDiffs.md

Advanced Git

Exercise Five - History and Diffs

Overview

In this exercise, we'll practice making a good commit, take a look at some of the interesting command line arguments for git log, use git show to get more information about a commit, then take a quick look at git branch.

Prerequisite

You should have the advanced-git-exercises repository cloned locally. Checkout the exercise5 branch:

$> git checkout exercise5
Switched to a new branch 'exercise5'

Exercise

1. Practice creating a well-crafted commit - look at the format given on the slides for help.
2. Use git log to find commits created since yesterday. Rename a file and use the --name-status and --follow options to git log to track down when the file was renamed, and what it used to be called. Use --grep to search within commit messages, and --diff-filter to find renamed and modified files from git log.
3. Use git show to get more information about a specific git hash.
4. Try the --merged and --no-merged options to git branch to see which branches have been merged into master (or not).

Solutions

Step 1 - Make a Good Commit

We've all made commits with short, silly, or otherwise unhelpful messages. Let's practice making a solid commit message for use in this example.

# Change your `hello.txt` to say [greeting] [noun]!

$> cat hello.txt
[greeting] [noun]!
This is a test of the emergency git-casting system.

# Rename hello.txt to hello.template

$> git mv hello.txt hello.template

$> git add hello.template

$> git commit

# This will open your text editor
# Type the following...
Replacing greeting with tokens for i18n

Currently, hello.txt contains both Spanish and English.
Let's replace Hola with a [greeting] token, and Mundo
with a [noun] token. That way, we can localize hello.txt for
any language!

# Save and exit your editor

[exercise5 4b2b90e] Replacing greeting with tokens for i18n
 1 file changed, 1 insertion(+), 1 deletion(-)

Step 2 - Git Log

Let's take a look at our new commit using git log. First we'll see how to see all commits in the log since yesterday:

$> git log --since="yesterday"
commit 4b2b90ec4f526139ca9c81e22174ebf5b9c56b52
Author: Nina Zakharenko <[email protected]>
Date:   Wed Oct 4 20:46:45 2017 -0700

    Replacing greeting with tokens for i18n

    Currently, hello.txt contains both Spanish and English.
    Let's replace Hola with a [greeting] token, and Mundo
    with a [noun] token. That way, we can localize hello.txt for
    any language!

Things can get tricky when trying to track down changes to files when they've been renamed. Here we see how to use git log to find the commit where hello.txt was renamed to hello.template. The --follow command will continue following the file backward in history, showing its filename for every commit:

$> git log --name-status --follow --oneline hello.template
4b2b90e Replacing greeting with tokens for i18n
R073    hello.txt       hello.template
fec9e7b Changing Hello to Hola
M       hello.txt
afa34a6 Changing World to Mundo
M       hello.txt
e348ebc Testing the emergency git-casting system
M       hello.txt
43388fe Initial commit
A       hello.txt

Ever spent too much time trying to track down a commit in Github? Use git log --grep to quickly find a commit. We can chain this with other flags. Let's find all the internationalization commits that the author Nina has added in the last two weeks:

$> git log --grep=i18n --author=nina --since=2.weeks
commit 4b2b90ec4f526139ca9c81e22174ebf5b9c56b52
Author: Nina Zakharenko <[email protected]>
Date:   Wed Oct 4 20:46:45 2017 -0700

    Replacing greeting with tokens for i18n

    Currently, hello.txt contains both Spanish and English.
    Let's replace Hola with a [greeting] token, and Mundo
    with a [noun] token. That way, we can localize hello.txt for
    any language!

We can use --diff-filter to find commits where files have been renamed:

$> git log --diff-filter=R --find-renames
4b2b90e Replacing greeting with tokens for i18n

Or to find commits where files have been modified:

$> git log --diff-filter=M --oneline
fec9e7b Changing Hello to Hola
afa34a6 Changing World to Mundo
e348ebc Testing the emergency git-casting system

Step 3 - Git Show

Now that we've mastered git log, how do we actually see what happened in a commit? Let's use git show to find out.

$> git log --grep=i18n --oneline
4b2b90e Replacing greeting with tokens for i18n

# Let's see the full commit and diff for 4b2b90e

$> git show 4b2b90e
commit 4b2b90ec4f526139ca9c81e22174ebf5b9c56b52
Author: Nina Zakharenko <[email protected]>
Date:   Wed Oct 4 20:46:45 2017 -0700

    Replacing greeting with tokens for i18n

    Currently, hello.txt contains both Spanish and English.
    Let's replace Hola with a [greeting] token, and Mundo
    with a [noun] token. That way, we can localize hello.txt for
    any language!

diff --git a/hello.template b/hello.template
new file mode 100644
index 0000000..a6c57ac
--- /dev/null
+++ b/hello.template
@@ -0,0 +1,2 @@
+[greeting] [noun]!
+This is a test of the emergency git-casting system.
diff --git a/hello.txt b/hello.txt
deleted file mode 100644
index 7018e35..0000000
--- a/hello.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-Hola Mundo!
-This is a test of the emergency git-casting system.

# Show the files changed in 4b2b90e

$> git show 4b2b90e --stat --oneline
4b2b90e Replacing greeting with tokens for i18n
 hello.template | 2 ++
 hello.txt      | 2 --
 2 files changed, 2 insertions(+), 2 deletions(-)

Step 4 - Git Branch

Let's say you're working on a complicated codebase with a master branch and lots of feature branches. Some of your coworkers forget to clean up their branches when they're done (we're all guilty). Which branches have been merged into master and can be cleaned up? Which branches haven't been merged yet? If you've been following along, yours may look different.

$> git branch --merged master
  exercise2
  exercise4
  master

$> git branch --no-merged master
  exercise3
* exercise5
  mundo

End of Exercise Five