History
Logging
As we already know, Git keeps track of every commit that we make. Because of that, we can easily review them in the so-called log.
$ git log
//Output Below
commit ff698ab Author: Elliot <elliot@allsafe.com> Date: Tue Nov 15 14:28 2016 Add cookie
Nice! git log brings up the commit history, where every commit is displayed with a unique hash code.
Logging again
Let's commit again to see multiple commits in the Git log. This time, let's also add a message.
$ touch cat.gif $ git add cat.gif $ git commit -m "Hello friend" $ git log
//Output Below
commit 7c1b0c4 Author: Elliot <elliot@allsafe.com> Date: Tue Nov 15 14:49 2016 Hello friend commit ff698ab Author: Elliot <elliot@allsafe.com> Date: Tue Nov 15 14:28 2016 Add cookie
Nice! Now git log reveals both of the commits we've made so far. From the commit messages we get an idea of what we've changed.
HEAD
The so-called HEAD is a pointer that points to the current commit.
$ git show HEAD
//Output Below
commit 7c1b0c4 Author: Elliot <elliot@allsafe.com> Date: Tue Nov 15 14:49 2016 Add cat
Sweet! Using git show, we can see that the HEAD is pointing to the commit with the hash code 7c1b0c4.
Turning back time
We can easily go back to a previous commit and put the working directory back to the state it was in at the time.
$ git checkout f871379
//Output Below
Note: checking out 'f871379'. You are in 'detached HEAD' state. HEAD is now at f871379... Add cookie
Perfect! Now (almost) everything is like it was when we made that commit.
Psst: we can either use the first seven characters or the whole hash code.
Lost in time
When we go back to a previous commit, we can see each file as it was when we made the commit but adding or changing files in there isn't a good idea.
$ git checkout f871379 Note: checking out 'f871379'. You are in 'detached HEAD' state. HEAD is now at f871379... Add cookie.txt $ touch cake.txt $ git status
//Output Below
HEAD detached at f871379 Untracked files: cake.txt
See that? Now the current commit isn't the latest commit anymore, which means we're in detached HEAD state, in which committing can lead to data losses.
Back to the future
Be gone, detached HEAD, we're going back to the future!
$ git checkout master
//Output Below
Previous HEAD position was f871379 Add cookie.txt Switched to branch 'master'
Great Scott, that's it! Using checkout master, we can go back to the latest commit, where everything is okay again.
Psst: now the HEAD points to the latest commit again.
Tagging
Instead of using and having to remember hash codes, we can also put tags on commits.
$ git checkout f871379 HEAD is now at f871379 Add cookie and cake $ git tag v1.2 $ git tag
//Output Below
v1.2
See that? We use git tag with a parameter to add a tag and the command without any parameters to display the previously added tags.
Checking out tags
We can also use tags in combination with the checkout command.
$ git tag v1.2 $ git checkout v1.2
//Output Below
Note: checking out 'v1.2'. You are in 'detached HEAD' state. HEAD is now at f871379 Add cookie and cake
Again, we are back at commit f871379. Using tags can help us memorize important commits.
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