                                   Git Basics

   If you can read only one chapter to get going with Git, this is it. This
   chapter covers every basic command you need to do the vast majority of the
   things you’ll eventually spend your time doing with Git. By the end of the
   chapter, you should be able to configure and initialize a repository,
   begin and stop tracking files, and stage and commit changes. We’ll also
   show you how to set up Git to ignore certain files and file patterns, how
   to undo mistakes quickly and easily, how to browse the history of your
   project and view changes between commits, and how to push and pull from
   remote repositories.

Getting a Git Repository

   You typically obtain a Git repository in one of two ways:

    1. You can take a local directory that is currently not under version
       control, and turn it into a Git repository, or
    2. You can clone an existing Git repository from elsewhere.

   In either case, you end up with a Git repository on your local machine,
   ready for work.

  Initializing a Repository in an Existing Directory

   If you have a project directory that is currently not under version
   control and you want to start controlling it with Git, you first need to
   go to that project’s directory. If you’ve never done this, it looks a
   little different depending on which system you’re running:

   for Linux:

 $ cd /home/user/my_project

   for macOS:

 $ cd /Users/user/my_project

   for Windows:

 $ cd C:/Users/user/my_project

   and type:

 $ git init

   This creates a new subdirectory named .git that contains all of your
   necessary repository files — a Git repository skeleton. At this point,
   nothing in your project is tracked yet. See Git Internals for more
   information about exactly what files are contained in the .git directory
   you just created.

   If you want to start version-controlling existing files (as opposed to an
   empty directory), you should probably begin tracking those files and do an
   initial commit. You can accomplish that with a few git add commands that
   specify the files you want to track, followed by a git commit:

 $ git add *.c
 $ git add LICENSE
 $ git commit -m 'Initial project version'

   We’ll go over what these commands do in just a minute. At this point, you
   have a Git repository with tracked files and an initial commit.

  Cloning an Existing Repository

   If you want to get a copy of an existing Git repository — for example, a
   project you’d like to contribute to — the command you need is git clone.
   If you’re familiar with other VCSs such as Subversion, you’ll notice that
   the command is "clone" and not "checkout". This is an important
   distinction — instead of getting just a working copy, Git receives a full
   copy of nearly all data that the server has. Every version of every file
   for the history of the project is pulled down by default when you run git
   clone. In fact, if your server disk gets corrupted, you can often use
   nearly any of the clones on any client to set the server back to the state
   it was in when it was cloned (you may lose some server-side hooks and
   such, but all the versioned data would be there — see Getting Git on a
   Server for more details).

   You clone a repository with git clone <url>. For example, if you want to
   clone the Git linkable library called libgit2, you can do so like this:

 $ git clone https://github.com/libgit2/libgit2

   That creates a directory named libgit2, initializes a .git directory
   inside it, pulls down all the data for that repository, and checks out a
   working copy of the latest version. If you go into the new libgit2
   directory that was just created, you’ll see the project files in there,
   ready to be worked on or used.

   If you want to clone the repository into a directory named something other
   than libgit2, you can specify the new directory name as an additional
   argument:

 $ git clone https://github.com/libgit2/libgit2 mylibgit

   That command does the same thing as the previous one, but the target
   directory is called mylibgit.

   Git has a number of different transfer protocols you can use. The previous
   example uses the https:// protocol, but you may also see git:// or
   user@server:path/to/repo.git, which uses the SSH transfer protocol.
   Getting Git on a Server will introduce all of the available options the
   server can set up to access your Git repository and the pros and cons of
   each.

Recording Changes to the Repository

   At this point, you should have a bona fide Git repository on your local
   machine, and a checkout or working copy of all of its files in front of
   you. Typically, you’ll want to start making changes and committing
   snapshots of those changes into your repository each time the project
   reaches a state you want to record.

   Remember that each file in your working directory can be in one of two
   states: tracked or untracked. Tracked files are files that were in the
   last snapshot, as well as any newly staged files; they can be unmodified,
   modified, or staged. In short, tracked files are files that Git knows
   about.

   Untracked files are everything else — any files in your working directory
   that were not in your last snapshot and are not in your staging area. When
   you first clone a repository, all of your files will be tracked and
   unmodified because Git just checked them out and you haven’t edited
   anything.

   As you edit files, Git sees them as modified, because you’ve changed them
   since your last commit. As you work, you selectively stage these modified
   files and then commit all those staged changes, and the cycle repeats.

   The lifecycle of the status of your files
   Figure 8. The lifecycle of the status of your files

  Checking the Status of Your Files

   The main tool you use to determine which files are in which state is the
   git status command. If you run this command directly after a clone, you
   should see something like this:

 $ git status
 On branch master
 Your branch is up-to-date with 'origin/master'.
 nothing to commit, working tree clean

   This means you have a clean working directory; in other words, none of
   your tracked files are modified. Git also doesn’t see any untracked files,
   or they would be listed here. Finally, the command tells you which branch
   you’re on and informs you that it has not diverged from the same branch on
   the server. For now, that branch is always master, which is the default;
   you won’t worry about it here. Git Branching will go over branches and
   references in detail.

   Let’s say you add a new file to your project, a simple README file. If the
   file didn’t exist before, and you run git status, you see your untracked
   file like so:

 $ echo 'My Project' > README
 $ git status
 On branch master
 Your branch is up-to-date with 'origin/master'.
 Untracked files:
   (use "git add <file>..." to include in what will be committed)

     README

 nothing added to commit but untracked files present (use "git add" to track)

   You can see that your new README file is untracked, because it’s under the
   “Untracked files” heading in your status output. Untracked basically means
   that Git sees a file you didn’t have in the previous snapshot (commit),
   and which hasn’t yet been staged; Git won’t start including it in your
   commit snapshots until you explicitly tell it to do so. It does this so
   you don’t accidentally begin including generated binary files or other
   files that you did not mean to include. You do want to start including
   README, so let’s start tracking the file.

  Tracking New Files

   In order to begin tracking a new file, you use the command git add. To
   begin tracking the README file, you can run this:

 $ git add README

   If you run your status command again, you can see that your README file is
   now tracked and staged to be committed:

 $ git status
 On branch master
 Your branch is up-to-date with 'origin/master'.
 Changes to be committed:
   (use "git restore --staged <file>..." to unstage)

     new file:   README

   You can tell that it’s staged because it’s under the “Changes to be
   committed” heading. If you commit at this point, the version of the file
   at the time you ran git add is what will be in the subsequent historical
   snapshot. You may recall that when you ran git init earlier, you then ran
   git add <files> — that was to begin tracking files in your directory. The
   git add command takes a path name for either a file or a directory; if
   it’s a directory, the command adds all the files in that directory
   recursively.

  Staging Modified Files

   Let’s change a file that was already tracked. If you change a previously
   tracked file called CONTRIBUTING.md and then run your git status command
   again, you get something that looks like this:

 $ 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)

     new file:   README

 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:   CONTRIBUTING.md

   The CONTRIBUTING.md file appears under a section named “Changes not staged
   for commit” — which means that a file that is tracked has been modified in
   the working directory but not yet staged. To stage it, you run the git add
   command. git add is a multipurpose command — you use it to begin tracking
   new files, to stage files, and to do other things like marking
   merge-conflicted files as resolved. It may be helpful to think of it more
   as “add precisely this content to the next commit” rather than “add this
   file to the project”. Let’s run git add now to stage the CONTRIBUTING.md
   file, and then run git status again:

 $ git add CONTRIBUTING.md
 $ 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)

     new file:   README
     modified:   CONTRIBUTING.md

   Both files are staged and will go into your next commit. At this point,
   suppose you remember one little change that you want to make in
   CONTRIBUTING.md before you commit it. You open it again and make that
   change, and you’re ready to commit. However, let’s run git status one more
   time:

 $ vim CONTRIBUTING.md
 $ 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)

     new file:   README
     modified:   CONTRIBUTING.md

 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:   CONTRIBUTING.md

   What the heck? Now CONTRIBUTING.md is listed as both staged and unstaged.
   How is that possible? It turns out that Git stages a file exactly as it is
   when you run the git add command. If you commit now, the version of
   CONTRIBUTING.md as it was when you last ran the git add command is how it
   will go into the commit, not the version of the file as it looks in your
   working directory when you run git commit. If you modify a file after you
   run git add, you have to run git add again to stage the latest version of
   the file:

 $ git add CONTRIBUTING.md
 $ 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)

     new file:   README
     modified:   CONTRIBUTING.md

  Short Status

   While the git status output is pretty comprehensive, it’s also quite
   wordy. Git also has a short status flag so you can see your changes in a
   more compact way. If you run git status -s or git status --short you get a
   far more simplified output from the command:

 $ git status -s
  M README
 MM Rakefile
 A  lib/git.rb
 M  lib/simplegit.rb
 ?? LICENSE.txt

   New files that aren’t tracked have a ?? next to them, new files that have
   been added to the staging area have an A, modified files have an M and so
   on. There are two columns to the output — the left-hand column indicates
   the status of the staging area and the right-hand column indicates the
   status of the working tree. So for example in that output, the README file
   is modified in the working directory but not yet staged, while the
   lib/simplegit.rb file is modified and staged. The Rakefile was modified,
   staged and then modified again, so there are changes to it that are both
   staged and unstaged.

  Ignoring Files

   Often, you’ll have a class of files that you don’t want Git to
   automatically add or even show you as being untracked. These are generally
   automatically generated files such as log files or files produced by your
   build system. In such cases, you can create a file listing patterns to
   match them named .gitignore. Here is an example .gitignore file:

 $ cat .gitignore
 *.[oa]
 *~

   The first line tells Git to ignore any files ending in “.o” or
   “.a” — object and archive files that may be the product of building your
   code. The second line tells Git to ignore all files whose names end with a
   tilde (~), which is used by many text editors such as Emacs to mark
   temporary files. You may also include a log, tmp, or pid directory;
   automatically generated documentation; and so on. Setting up a .gitignore
   file for your new repository before you get going is generally a good idea
   so you don’t accidentally commit files that you really don’t want in your
   Git repository.

   The rules for the patterns you can put in the .gitignore file are as
   follows:

     * Blank lines or lines starting with # are ignored.
     * Standard glob patterns work, and will be applied recursively
       throughout the entire working tree.
     * You can start patterns with a forward slash (/) to avoid recursivity.
     * You can end patterns with a forward slash (/) to specify a directory.
     * You can negate a pattern by starting it with an exclamation point (!).

   Glob patterns are like simplified regular expressions that shells use. An
   asterisk (*) matches zero or more characters; [abc] matches any character
   inside the brackets (in this case a, b, or c); a question mark (?) matches
   a single character; and brackets enclosing characters separated by a
   hyphen ([0-9]) matches any character between them (in this case 0 through
   9). You can also use two asterisks to match nested directories; a/**/z
   would match a/z, a/b/z, a/b/c/z, and so on.

   Here is another example .gitignore file:

 # ignore all .a files
 *.a

 # but do track lib.a, even though you're ignoring .a files above
 !lib.a

 # only ignore the TODO file in the current directory, not subdir/TODO
 /TODO

 # ignore all files in any directory named build
 build/

 # ignore doc/notes.txt, but not doc/server/arch.txt
 doc/*.txt

 # ignore all .pdf files in the doc/ directory and any of its subdirectories
 doc/**/*.pdf

   GitHub maintains a fairly comprehensive list of good .gitignore file
   examples for dozens of projects and languages at
   https://github.com/github/gitignore if you want a starting point for your
   project.

   In the simple case, a repository might have a single .gitignore file in
   its root directory, which applies recursively to the entire repository.
   However, it is also possible to have additional .gitignore files in
   subdirectories. The rules in these nested .gitignore files apply only to
   the files under the directory where they are located. The Linux kernel
   source repository has 206 .gitignore files.

   It is beyond the scope of this book to get into the details of multiple
   .gitignore files; see man gitignore for the details.

  Viewing Your Staged and Unstaged Changes

   If the git status command is too vague for you — you want to know exactly
   what you changed, not just which files were changed — you can use the git
   diff command. We’ll cover git diff in more detail later, but you’ll
   probably use it most often to answer these two questions: What have you
   changed but not yet staged? And what have you staged that you are about to
   commit? Although git status answers those questions very generally by
   listing the file names, git diff shows you the exact lines added and
   removed — the patch, as it were.

   Let’s say you edit and stage the README file again and then edit the
   CONTRIBUTING.md file without staging it. If you run your git status
   command, you once again see something like this:

 $ 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

 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:   CONTRIBUTING.md

   To see what you’ve changed but not yet staged, type git diff with no other
   arguments:

 $ git diff
 diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
 index 8ebb991..643e24f 100644
 --- a/CONTRIBUTING.md
 +++ b/CONTRIBUTING.md
 @@ -65,7 +65,8 @@ branch directly, things can get messy.
  Please include a nice description of your changes when you submit your PR;
  if we have to read the whole diff to figure out why you're contributing
  in the first place, you're less likely to get feedback and have your change
 -merged in.
 +merged in. Also, split your changes into comprehensive chunks if your patch is
 +longer than a dozen lines.

  If you are starting to work on a particular area, feel free to submit a PR
  that highlights your work in progress (and note in the PR title that it's

   That command compares what is in your working directory with what is in
   your staging area. The result tells you the changes you’ve made that you
   haven’t yet staged.

   If you want to see what you’ve staged that will go into your next commit,
   you can use git diff --staged. This command compares your staged changes
   to your last commit:

 $ git diff --staged
 diff --git a/README b/README
 new file mode 100644
 index 0000000..03902a1
 --- /dev/null
 +++ b/README
 @@ -0,0 +1 @@
 +My Project

   It’s important to note that git diff by itself doesn’t show all changes
   made since your last commit — only changes that are still unstaged. If
   you’ve staged all of your changes, git diff will give you no output.

   For another example, if you stage the CONTRIBUTING.md file and then edit
   it, you can use git diff to see the changes in the file that are staged
   and the changes that are unstaged. If our environment looks like this:

 $ git add CONTRIBUTING.md
 $ echo '# test line' >> CONTRIBUTING.md
 $ 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:   CONTRIBUTING.md

 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:   CONTRIBUTING.md

   Now you can use git diff to see what is still unstaged:

 $ git diff
 diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
 index 643e24f..87f08c8 100644
 --- a/CONTRIBUTING.md
 +++ b/CONTRIBUTING.md
 @@ -119,3 +119,4 @@ at the
  ## Starter Projects

  See our [projects list](https://github.com/libgit2/libgit2/blob/development/PROJECTS.md).
 +# test line

   and git diff --cached to see what you’ve staged so far (--staged and
   --cached are synonyms):

 $ git diff --cached
 diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
 index 8ebb991..643e24f 100644
 --- a/CONTRIBUTING.md
 +++ b/CONTRIBUTING.md
 @@ -65,7 +65,8 @@ branch directly, things can get messy.
  Please include a nice description of your changes when you submit your PR;
  if we have to read the whole diff to figure out why you're contributing
  in the first place, you're less likely to get feedback and have your change
 -merged in.
 +merged in. Also, split your changes into comprehensive chunks if your patch is
 +longer than a dozen lines.

  If you are starting to work on a particular area, feel free to submit a PR
  that highlights your work in progress (and note in the PR title that it's

Git Diff in an External Tool

   We will continue to use the git diff command in various ways throughout
   the rest of the book. There is another way to look at these diffs if you
   prefer a graphical or external diff viewing program instead. If you run
   git difftool instead of git diff, you can view any of these diffs in
   software like emerge, vimdiff and many more (including commercial
   products). Run git difftool --tool-help to see what is available on your
   system.

  Committing Your Changes

   Now that your staging area is set up the way you want it, you can commit
   your changes. Remember that anything that is still unstaged — any files
   you have created or modified that you haven’t run git add on since you
   edited them — won’t go into this commit. They will stay as modified files
   on your disk. In this case, let’s say that the last time you ran git
   status, you saw that everything was staged, so you’re ready to commit your
   changes. The simplest way to commit is to type git commit:

 $ git commit

   Doing so launches your editor of choice.

   This is set by your shell’s EDITOR environment variable — usually vim or
   emacs, although you can configure it with whatever you want using the git
   config --global core.editor command as you saw in Getting Started.

   The editor displays the following text (this example is a Vim screen):

 # Please enter the commit message for your changes. Lines starting
 # with '#' will be ignored, and an empty message aborts the commit.
 # On branch master
 # Your branch is up-to-date with 'origin/master'.
 #
 # Changes to be committed:
 #       new file:   README
 #       modified:   CONTRIBUTING.md
 #
 ~
 ~
 ~
 ".git/COMMIT_EDITMSG" 9L, 283C

   You can see that the default commit message contains the latest output of
   the git status command commented out and one empty line on top. You can
   remove these comments and type your commit message, or you can leave them
   there to help you remember what you’re committing.

   For an even more explicit reminder of what you’ve modified, you can pass
   the -v option to git commit. Doing so also puts the diff of your change in
   the editor so you can see exactly what changes you’re committing.

   When you exit the editor, Git creates your commit with that commit message
   (with the comments and diff stripped out).

   Alternatively, you can type your commit message inline with the commit
   command by specifying it after a -m flag, like this:

 $ git commit -m "Story 182: fix benchmarks for speed"
 [master 463dc4f] Story 182: fix benchmarks for speed
  2 files changed, 2 insertions(+)
  create mode 100644 README

   Now you’ve created your first commit! You can see that the commit has
   given you some output about itself: which branch you committed to
   (master), what SHA-1 checksum the commit has (463dc4f), how many files
   were changed, and statistics about lines added and removed in the commit.

   Remember that the commit records the snapshot you set up in your staging
   area. Anything you didn’t stage is still sitting there modified; you can
   do another commit to add it to your history. Every time you perform a
   commit, you’re recording a snapshot of your project that you can revert to
   or compare to later.

  Skipping the Staging Area

   Although it can be amazingly useful for crafting commits exactly how you
   want them, the staging area is sometimes a bit more complex than you need
   in your workflow. If you want to skip the staging area, Git provides a
   simple shortcut. Adding the -a option to the git commit command makes Git
   automatically stage every file that is already tracked before doing the
   commit, letting you skip the git add part:

 $ 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:   CONTRIBUTING.md

 no changes added to commit (use "git add" and/or "git commit -a")
 $ git commit -a -m 'Add new benchmarks'
 [master 83e38c7] Add new benchmarks
  1 file changed, 5 insertions(+), 0 deletions(-)

   Notice how you don’t have to run git add on the CONTRIBUTING.md file in
   this case before you commit. That’s because the -a flag includes all
   changed files. This is convenient, but be careful; sometimes this flag
   will cause you to include unwanted changes.

  Removing Files

   To remove a file from Git, you have to remove it from your tracked files
   (more accurately, remove it from your staging area) and then commit. The
   git rm command does that, and also removes the file from your working
   directory so you don’t see it as an untracked file the next time around.

   If you simply remove the file from your working directory, it shows up
   under the “Changes not staged for commit” (that is, unstaged) area of your
   git status output:

 $ rm PROJECTS.md
 $ git status
 On branch master
 Your branch is up-to-date with 'origin/master'.
 Changes not staged for commit:
   (use "git add/rm <file>..." to update what will be committed)
   (use "git checkout -- <file>..." to discard changes in working directory)

         deleted:    PROJECTS.md

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

   Then, if you run git rm, it stages the file’s removal:

 $ git rm PROJECTS.md
 rm 'PROJECTS.md'
 $ 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)

     deleted:    PROJECTS.md

   The next time you commit, the file will be gone and no longer tracked. If
   you modified the file or had already added it to the staging area, you
   must force the removal with the -f option. This is a safety feature to
   prevent accidental removal of data that hasn’t yet been recorded in a
   snapshot and that can’t be recovered from Git.

   Another useful thing you may want to do is to keep the file in your
   working tree but remove it from your staging area. In other words, you may
   want to keep the file on your hard drive but not have Git track it
   anymore. This is particularly useful if you forgot to add something to
   your .gitignore file and accidentally staged it, like a large log file or
   a bunch of .a compiled files. To do this, use the --cached option:

 $ git rm --cached README

   You can pass files, directories, and file-glob patterns to the git rm
   command. That means you can do things such as:

 $ git rm log/\*.log

   Note the backslash (\) in front of the *. This is necessary because Git
   does its own filename expansion in addition to your shell’s filename
   expansion. This command removes all files that have the .log extension in
   the log/ directory. Or, you can do something like this:

 $ git rm \*~

   This command removes all files whose names end with a ~.

  Moving Files

   Unlike many other VCSs, Git doesn’t explicitly track file movement. If you
   rename a file in Git, no metadata is stored in Git that tells it you
   renamed the file. However, Git is pretty smart about figuring that out
   after the fact — we’ll deal with detecting file movement a bit later.

   Thus it’s a bit confusing that Git has a mv command. If you want to rename
   a file in Git, you can run something like:

 $ git mv file_from file_to

   and it works fine. In fact, if you run something like this and look at the
   status, you’ll see that Git considers it a renamed file:

 $ git mv README.md README
 $ 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)

     renamed:    README.md -> README

   However, this is equivalent to running something like this:

 $ mv README.md README
 $ git rm README.md
 $ git add README

   Git figures out that it’s a rename implicitly, so it doesn’t matter if you
   rename a file that way or with the mv command. The only real difference is
   that git mv is one command instead of three — it’s a convenience function.
   More importantly, you can use any tool you like to rename a file, and
   address the add/rm later, before you commit.

Viewing the Commit History

   After you have created several commits, or if you have cloned a repository
   with an existing commit history, you’ll probably want to look back to see
   what has happened. The most basic and powerful tool to do this is the git
   log command.

   These examples use a very simple project called “simplegit”. To get the
   project, run:

 $ git clone https://github.com/schacon/simplegit-progit

   When you run git log in this project, you should get output that looks
   something like this:

 $ git log
 commit ca82a6dff817ec66f44342007202690a93763949
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Mon Mar 17 21:52:11 2008 -0700

     Change version number

 commit 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Sat Mar 15 16:40:33 2008 -0700

     Remove unnecessary test

 commit a11bef06a3f659402fe7563abf99ad00de2209e6
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Sat Mar 15 10:31:28 2008 -0700

     Initial commit

   By default, with no arguments, git log lists the commits made in that
   repository in reverse chronological order; that is, the most recent
   commits show up first. As you can see, this command lists each commit with
   its SHA-1 checksum, the author’s name and email, the date written, and the
   commit message.

   A huge number and variety of options to the git log command are available
   to show you exactly what you’re looking for. Here, we’ll show you some of
   the most popular.

   One of the more helpful options is -p or --patch, which shows the
   difference (the patch output) introduced in each commit. You can also
   limit the number of log entries displayed, such as using -2 to show only
   the last two entries.

 $ git log -p -2
 commit ca82a6dff817ec66f44342007202690a93763949
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Mon Mar 17 21:52:11 2008 -0700

     Change version number

 diff --git a/Rakefile b/Rakefile
 index a874b73..8f94139 100644
 --- a/Rakefile
 +++ b/Rakefile
 @@ -5,7 +5,7 @@ require 'rake/gempackagetask'
  spec = Gem::Specification.new do |s|
      s.platform  =   Gem::Platform::RUBY
      s.name      =   "simplegit"
 -    s.version   =   "0.1.0"
 +    s.version   =   "0.1.1"
      s.author    =   "Scott Chacon"
      s.email     =   "schacon@gee-mail.com"
      s.summary   =   "A simple gem for using Git in Ruby code."

 commit 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Sat Mar 15 16:40:33 2008 -0700

     Remove unnecessary test

 diff --git a/lib/simplegit.rb b/lib/simplegit.rb
 index a0a60ae..47c6340 100644
 --- a/lib/simplegit.rb
 +++ b/lib/simplegit.rb
 @@ -18,8 +18,3 @@ class SimpleGit
      end

  end
 -
 -if $0 == __FILE__
 -  git = SimpleGit.new
 -  puts git.show
 -end

   This option displays the same information but with a diff directly
   following each entry. This is very helpful for code review or to quickly
   browse what happened during a series of commits that a collaborator has
   added. You can also use a series of summarizing options with git log. For
   example, if you want to see some abbreviated stats for each commit, you
   can use the --stat option:

 $ git log --stat
 commit ca82a6dff817ec66f44342007202690a93763949
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Mon Mar 17 21:52:11 2008 -0700

     Change version number

  Rakefile | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

 commit 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Sat Mar 15 16:40:33 2008 -0700

     Remove unnecessary test

  lib/simplegit.rb | 5 -----
  1 file changed, 5 deletions(-)

 commit a11bef06a3f659402fe7563abf99ad00de2209e6
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Sat Mar 15 10:31:28 2008 -0700

     Initial commit

  README           |  6 ++++++
  Rakefile         | 23 +++++++++++++++++++++++
  lib/simplegit.rb | 25 +++++++++++++++++++++++++
  3 files changed, 54 insertions(+)

   As you can see, the --stat option prints below each commit entry a list of
   modified files, how many files were changed, and how many lines in those
   files were added and removed. It also puts a summary of the information at
   the end.

   Another really useful option is --pretty. This option changes the log
   output to formats other than the default. A few prebuilt option values are
   available for you to use. The oneline value for this option prints each
   commit on a single line, which is useful if you’re looking at a lot of
   commits. In addition, the short, full, and fuller values show the output
   in roughly the same format but with less or more information,
   respectively:

 $ git log --pretty=oneline
 ca82a6dff817ec66f44342007202690a93763949 Change version number
 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 Remove unnecessary test
 a11bef06a3f659402fe7563abf99ad00de2209e6 Initial commit

   The most interesting option value is format, which allows you to specify
   your own log output format. This is especially useful when you’re
   generating output for machine parsing — because you specify the format
   explicitly, you know it won’t change with updates to Git:

 $ git log --pretty=format:"%h - %an, %ar : %s"
 ca82a6d - Scott Chacon, 6 years ago : Change version number
 085bb3b - Scott Chacon, 6 years ago : Remove unnecessary test
 a11bef0 - Scott Chacon, 6 years ago : Initial commit

   Useful specifiers for git log --pretty=format lists some of the more
   useful specifiers that format takes.

             Table 1. Useful specifiers for git log --pretty=format
   Specifier Description of Output                           
   %H        Commit hash                                     
   %h        Abbreviated commit hash                         
   %T        Tree hash                                       
   %t        Abbreviated tree hash                           
   %P        Parent hashes                                   
   %p        Abbreviated parent hashes                       
   %an       Author name                                     
   %ae       Author email                                    
   %ad       Author date (format respects the --date=option) 
   %ar       Author date, relative                           
   %cn       Committer name                                  
   %ce       Committer email                                 
   %cd       Committer date                                  
   %cr       Committer date, relative                        
   %s        Subject                                         

   You may be wondering what the difference is between author and committer.
   The author is the person who originally wrote the work, whereas the
   committer is the person who last applied the work. So, if you send in a
   patch to a project and one of the core members applies the patch, both of
   you get credit — you as the author, and the core member as the committer.
   We’ll cover this distinction a bit more in Distributed Git.

   The oneline and format option values are particularly useful with another
   log option called --graph. This option adds a nice little ASCII graph
   showing your branch and merge history:

 $ git log --pretty=format:"%h %s" --graph
 * 2d3acf9 Ignore errors from SIGCHLD on trap
 *  5e3ee11 Merge branch 'master' of git://github.com/dustin/grit
 |\
 | * 420eac9 Add method for getting the current branch
 * | 30e367c Timeout code and tests
 * | 5a09431 Add timeout protection to grit
 * | e1193f8 Support for heads with slashes in them
 |/
 * d6016bc Require time for xmlschema
 *  11d191e Merge branch 'defunkt' into local

   This type of output will become more interesting as we go through
   branching and merging in the next chapter.

   Those are only some simple output-formatting options to git log — there
   are many more. Common options to git log lists the options we’ve covered
   so far, as well as some other common formatting options that may be
   useful, along with how they change the output of the log command.

                       Table 2. Common options to git log
   Option          Description                                                
   -p              Show the patch introduced with each commit.                
   --stat          Show statistics for files modified in each commit.         
   --shortstat     Display only the changed/insertions/deletions line from    
                   the --stat command.                                        
   --name-only     Show the list of files modified after the commit           
                   information.                                               
   --name-status   Show the list of files affected with                       
                   added/modified/deleted information as well.                
   --abbrev-commit Show only the first few characters of the SHA-1 checksum   
                   instead of all 40.                                         
   --relative-date Display the date in a relative format (for example, “2     
                   weeks ago”) instead of using the full date format.         
   --graph         Display an ASCII graph of the branch and merge history     
                   beside the log output.                                     
                   Show commits in an alternate format. Option values include 
   --pretty        oneline, short, full, fuller, and format (where you        
                   specify your own format).                                  
   --oneline       Shorthand for --pretty=oneline --abbrev-commit used        
                   together.                                                  

  Limiting Log Output

   In addition to output-formatting options, git log takes a number of useful
   limiting options; that is, options that let you show only a subset of
   commits. You’ve seen one such option already — the -2 option, which
   displays only the last two commits. In fact, you can do -<n>, where n is
   any integer to show the last n commits. In reality, you’re unlikely to use
   that often, because Git by default pipes all output through a pager so you
   see only one page of log output at a time.

   However, the time-limiting options such as --since and --until are very
   useful. For example, this command gets the list of commits made in the
   last two weeks:

 $ git log --since=2.weeks

   This command works with lots of formats — you can specify a specific date
   like "2008-01-15", or a relative date such as "2 years 1 day 3 minutes
   ago".

   You can also filter the list to commits that match some search criteria.
   The --author option allows you to filter on a specific author, and the
   --grep option lets you search for keywords in the commit messages.

   You can specify more than one instance of both the --author and --grep
   search criteria, which will limit the commit output to commits that match
   any of the --author patterns and any of the --grep patterns; however,
   adding the --all-match option further limits the output to just those
   commits that match all --grep patterns.

   Another really helpful filter is the -S option (colloquially referred to
   as Git’s “pickaxe” option), which takes a string and shows only those
   commits that changed the number of occurrences of that string. For
   instance, if you wanted to find the last commit that added or removed a
   reference to a specific function, you could call:

 $ git log -S function_name

   The last really useful option to pass to git log as a filter is a path. If
   you specify a directory or file name, you can limit the log output to
   commits that introduced a change to those files. This is always the last
   option and is generally preceded by double dashes (--) to separate the
   paths from the options:

 $ git log -- path/to/file

   In Options to limit the output of git log we’ll list these and a few other
   common options for your reference.

                Table 3. Options to limit the output of git log
   Option            Description                                              
   -<n>              Show only the last n commits                             
   --since, --after  Limit the commits to those made after the specified      
                     date.                                                    
   --until, --before Limit the commits to those made before the specified     
                     date.                                                    
   --author          Only show commits in which the author entry matches the  
                     specified string.                                        
   --committer       Only show commits in which the committer entry matches   
                     the specified string.                                    
   --grep            Only show commits with a commit message containing the   
                     string                                                   
   -S                Only show commits adding or removing code matching the   
                     string                                                   

   For example, if you want to see which commits modifying test files in the
   Git source code history were committed by Junio Hamano in the month of
   October 2008 and are not merge commits, you can run something like this:

 $ git log --pretty="%h - %s" --author='Junio C Hamano' --since="2008-10-01" \
    --before="2008-11-01" --no-merges -- t/
 5610e3b - Fix testcase failure when extended attributes are in use
 acd3b9e - Enhance hold_lock_file_for_{update,append}() API
 f563754 - demonstrate breakage of detached checkout with symbolic link HEAD
 d1a43f2 - reset --hard/read-tree --reset -u: remove unmerged new paths
 51a94af - Fix "checkout --track -b newbranch" on detached HEAD
 b0ad11e - pull: allow "git pull origin $something:$current_branch" into an unborn branch

   Of the nearly 40,000 commits in the Git source code history, this command
   shows the 6 that match those criteria.

Preventing the display of merge commits

   Depending on the workflow used in your repository, it’s possible that a
   sizable percentage of the commits in your log history are just merge
   commits, which typically aren’t very informative. To prevent the display
   of merge commits cluttering up your log history, simply add the log option
   --no-merges.

Undoing Things

   At any stage, you may want to undo something. Here, we’ll review a few
   basic tools for undoing changes that you’ve made. Be careful, because you
   can’t always undo some of these undos. This is one of the few areas in Git
   where you may lose some work if you do it wrong.

   One of the common undos takes place when you commit too early and possibly
   forget to add some files, or you mess up your commit message. If you want
   to redo that commit, make the additional changes you forgot, stage them,
   and commit again using the --amend option:

 $ git commit --amend

   This command takes your staging area and uses it for the commit. If you’ve
   made no changes since your last commit (for instance, you run this command
   immediately after your previous commit), then your snapshot will look
   exactly the same, and all you’ll change is your commit message.

   The same commit-message editor fires up, but it already contains the
   message of your previous commit. You can edit the message the same as
   always, but it overwrites your previous commit.

   As an example, if you commit and then realize you forgot to stage the
   changes in a file you wanted to add to this commit, you can do something
   like this:

 $ git commit -m 'Initial commit'
 $ git add forgotten_file
 $ git commit --amend

   You end up with a single commit — the second commit replaces the results
   of the first.

   It’s important to understand that when you’re amending your last commit,
   you’re not so much fixing it as replacing it entirely with a new, improved
   commit that pushes the old commit out of the way and puts the new commit
   in its place. Effectively, it’s as if the previous commit never happened,
   and it won’t show up in your repository history.

   The obvious value to amending commits is to make minor improvements to
   your last commit, without cluttering your repository history with commit
   messages of the form, “Oops, forgot to add a file” or “Darn, fixing a typo
   in last commit”.

   Only amend commits that are still local and have not been pushed
   somewhere. Amending previously pushed commits and force pushing the branch
   will cause problems for your collaborators. For more on what happens when
   you do this and how to recover if you’re on the receiving end read The
   Perils of Rebasing.

  Unstaging a Staged File

   The next two sections demonstrate how to work with your staging area and
   working directory changes. The nice part is that the command you use to
   determine the state of those two areas also reminds you how to undo
   changes to them. For example, let’s say you’ve changed two files and want
   to commit them as two separate changes, but you accidentally type git add
   * and stage them both. How can you unstage one of the two? The git status
   command reminds you:

 $ git add *
 $ git status
 On branch master
 Changes to be committed:
   (use "git reset HEAD <file>..." to unstage)

     renamed:    README.md -> README
     modified:   CONTRIBUTING.md

   Right below the “Changes to be committed” text, it says use git reset HEAD
   <file>…​ to unstage. So, let’s use that advice to unstage the
   CONTRIBUTING.md file:

 $ git reset HEAD CONTRIBUTING.md
 Unstaged changes after reset:
 M       CONTRIBUTING.md
 $ git status
 On branch master
 Changes to be committed:
   (use "git reset HEAD <file>..." to unstage)

     renamed:    README.md -> README

 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:   CONTRIBUTING.md

   The command is a bit strange, but it works. The CONTRIBUTING.md file is
   modified but once again unstaged.

   It’s true that git reset can be a dangerous command, especially if you
   provide the --hard flag. However, in the scenario described above, the
   file in your working directory is not touched, so it’s relatively safe.

   For now this magic invocation is all you need to know about the git reset
   command. We’ll go into much more detail about what reset does and how to
   master it to do really interesting things in Reset Demystified.

  Unmodifying a Modified File

   What if you realize that you don’t want to keep your changes to the
   CONTRIBUTING.md file? How can you easily unmodify it — revert it back to
   what it looked like when you last committed (or initially cloned, or
   however you got it into your working directory)? Luckily, git status tells
   you how to do that, too. In the last example output, the unstaged area
   looks like this:

 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:   CONTRIBUTING.md

   It tells you pretty explicitly how to discard the changes you’ve made.
   Let’s do what it says:

 $ git checkout -- CONTRIBUTING.md
 $ git status
 On branch master
 Changes to be committed:
   (use "git reset HEAD <file>..." to unstage)

     renamed:    README.md -> README

   You can see that the changes have been reverted.

   It’s important to understand that git checkout -- <file> is a dangerous
   command. Any local changes you made to that file are gone — Git just
   replaced that file with the last staged or committed version. Don’t ever
   use this command unless you absolutely know that you don’t want those
   unsaved local changes.

   If you would like to keep the changes you’ve made to that file but still
   need to get it out of the way for now, we’ll go over stashing and
   branching in Git Branching; these are generally better ways to go.

   Remember, anything that is committed in Git can almost always be
   recovered. Even commits that were on branches that were deleted or commits
   that were overwritten with an --amend commit can be recovered (see Data
   Recovery for data recovery). However, anything you lose that was never
   committed is likely never to be seen again.

  Undoing things with git restore

   Git version 2.23.0 introduced a new command: git restore. It’s basically
   an alternative to git reset which we just covered. From Git version 2.23.0
   onwards, Git will use git restore instead of git reset for many undo
   operations.

   Let’s retrace our steps, and undo things with git restore instead of git
   reset.

    Unstaging a Staged File with git restore

   The next two sections demonstrate how to work with your staging area and
   working directory changes with git restore. The nice part is that the
   command you use to determine the state of those two areas also reminds you
   how to undo changes to them. For example, let’s say you’ve changed two
   files and want to commit them as two separate changes, but you
   accidentally type git add * and stage them both. How can you unstage one
   of the two? The git status command reminds you:

 $ git add *
 $ git status
 On branch master
 Changes to be committed:
   (use "git restore --staged <file>..." to unstage)
         modified:   CONTRIBUTING.md
         renamed:    README.md -> README

   Right below the “Changes to be committed” text, it says use git restore
   --staged <file>…​ to unstage. So, let’s use that advice to unstage the
   CONTRIBUTING.md file:

 $ git restore --staged CONTRIBUTING.md
 $ git status
 On branch master
 Changes to be committed:
   (use "git restore --staged <file>..." to unstage)
         renamed:    README.md -> README

 Changes not staged for commit:
   (use "git add <file>..." to update what will be committed)
   (use "git restore <file>..." to discard changes in working directory)
         modified:   CONTRIBUTING.md

   The CONTRIBUTING.md file is modified but once again unstaged.

    Unmodifying a Modified File with git restore

   What if you realize that you don’t want to keep your changes to the
   CONTRIBUTING.md file? How can you easily unmodify it — revert it back to
   what it looked like when you last committed (or initially cloned, or
   however you got it into your working directory)? Luckily, git status tells
   you how to do that, too. In the last example output, the unstaged area
   looks like this:

 Changes not staged for commit:
   (use "git add <file>..." to update what will be committed)
   (use "git restore <file>..." to discard changes in working directory)
         modified:   CONTRIBUTING.md

   It tells you pretty explicitly how to discard the changes you’ve made.
   Let’s do what it says:

 $ git restore CONTRIBUTING.md
 $ git status
 On branch master
 Changes to be committed:
   (use "git restore --staged <file>..." to unstage)
         renamed:    README.md -> README

   It’s important to understand that git restore <file> is a dangerous
   command. Any local changes you made to that file are gone — Git just
   replaced that file with the last staged or committed version. Don’t ever
   use this command unless you absolutely know that you don’t want those
   unsaved local changes.

Working with Remotes

   To be able to collaborate on any Git project, you need to know how to
   manage your remote repositories. Remote repositories are versions of your
   project that are hosted on the Internet or network somewhere. You can have
   several of them, each of which generally is either read-only or read/write
   for you. Collaborating with others involves managing these remote
   repositories and pushing and pulling data to and from them when you need
   to share work. Managing remote repositories includes knowing how to add
   remote repositories, remove remotes that are no longer valid, manage
   various remote branches and define them as being tracked or not, and more.
   In this section, we’ll cover some of these remote-management skills.

Remote repositories can be on your local machine.

   It is entirely possible that you can be working with a “remote” repository
   that is, in fact, on the same host you are. The word “remote” does not
   necessarily imply that the repository is somewhere else on the network or
   Internet, only that it is elsewhere. Working with such a remote repository
   would still involve all the standard pushing, pulling and fetching
   operations as with any other remote.

  Showing Your Remotes

   To see which remote servers you have configured, you can run the git
   remote command. It lists the shortnames of each remote handle you’ve
   specified. If you’ve cloned your repository, you should at least see
   origin — that is the default name Git gives to the server you cloned from:

 $ git clone https://github.com/schacon/ticgit
 Cloning into 'ticgit'...
 remote: Reusing existing pack: 1857, done.
 remote: Total 1857 (delta 0), reused 0 (delta 0)
 Receiving objects: 100% (1857/1857), 374.35 KiB | 268.00 KiB/s, done.
 Resolving deltas: 100% (772/772), done.
 Checking connectivity... done.
 $ cd ticgit
 $ git remote
 origin

   You can also specify -v, which shows you the URLs that Git has stored for
   the shortname to be used when reading and writing to that remote:

 $ git remote -v
 origin  https://github.com/schacon/ticgit (fetch)
 origin  https://github.com/schacon/ticgit (push)

   If you have more than one remote, the command lists them all. For example,
   a repository with multiple remotes for working with several collaborators
   might look something like this.

 $ cd grit
 $ git remote -v
 bakkdoor  https://github.com/bakkdoor/grit (fetch)
 bakkdoor  https://github.com/bakkdoor/grit (push)
 cho45     https://github.com/cho45/grit (fetch)
 cho45     https://github.com/cho45/grit (push)
 defunkt   https://github.com/defunkt/grit (fetch)
 defunkt   https://github.com/defunkt/grit (push)
 koke      git://github.com/koke/grit.git (fetch)
 koke      git://github.com/koke/grit.git (push)
 origin    git@github.com:mojombo/grit.git (fetch)
 origin    git@github.com:mojombo/grit.git (push)

   This means we can pull contributions from any of these users pretty
   easily. We may additionally have permission to push to one or more of
   these, though we can’t tell that here.

   Notice that these remotes use a variety of protocols; we’ll cover more
   about this in Getting Git on a Server.

  Adding Remote Repositories

   We’ve mentioned and given some demonstrations of how the git clone command
   implicitly adds the origin remote for you. Here’s how to add a new remote
   explicitly. To add a new remote Git repository as a shortname you can
   reference easily, run git remote add <shortname> <url>:

 $ git remote
 origin
 $ git remote add pb https://github.com/paulboone/ticgit
 $ git remote -v
 origin  https://github.com/schacon/ticgit (fetch)
 origin  https://github.com/schacon/ticgit (push)
 pb      https://github.com/paulboone/ticgit (fetch)
 pb      https://github.com/paulboone/ticgit (push)

   Now you can use the string pb on the command line in lieu of the whole
   URL. For example, if you want to fetch all the information that Paul has
   but that you don’t yet have in your repository, you can run git fetch pb:

 $ git fetch pb
 remote: Counting objects: 43, done.
 remote: Compressing objects: 100% (36/36), done.
 remote: Total 43 (delta 10), reused 31 (delta 5)
 Unpacking objects: 100% (43/43), done.
 From https://github.com/paulboone/ticgit
  * [new branch]      master     -> pb/master
  * [new branch]      ticgit     -> pb/ticgit

   Paul’s master branch is now accessible locally as pb/master — you can
   merge it into one of your branches, or you can check out a local branch at
   that point if you want to inspect it. We’ll go over what branches are and
   how to use them in much more detail in Git Branching.

  Fetching and Pulling from Your Remotes

   As you just saw, to get data from your remote projects, you can run:

 $ git fetch <remote>

   The command goes out to that remote project and pulls down all the data
   from that remote project that you don’t have yet. After you do this, you
   should have references to all the branches from that remote, which you can
   merge in or inspect at any time.

   If you clone a repository, the command automatically adds that remote
   repository under the name “origin”. So, git fetch origin fetches any new
   work that has been pushed to that server since you cloned (or last fetched
   from) it. It’s important to note that the git fetch command only downloads
   the data to your local repository — it doesn’t automatically merge it with
   any of your work or modify what you’re currently working on. You have to
   merge it manually into your work when you’re ready.

   If your current branch is set up to track a remote branch (see the next
   section and Git Branching for more information), you can use the git pull
   command to automatically fetch and then merge that remote branch into your
   current branch. This may be an easier or more comfortable workflow for
   you; and by default, the git clone command automatically sets up your
   local master branch to track the remote master branch (or whatever the
   default branch is called) on the server you cloned from. Running git pull
   generally fetches data from the server you originally cloned from and
   automatically tries to merge it into the code you’re currently working on.

   From git version 2.27 onward, git pull will give a warning if the
   pull.rebase variable is not set. Git will keep warning you until you set
   the variable.

   If you want the default behavior of git (fast-forward if possible, else
   create a merge commit): git config --global pull.rebase "false"

   If you want to rebase when pulling: git config --global pull.rebase "true"

  Pushing to Your Remotes

   When you have your project at a point that you want to share, you have to
   push it upstream. The command for this is simple: git push <remote>
   <branch>. If you want to push your master branch to your origin server
   (again, cloning generally sets up both of those names for you
   automatically), then you can run this to push any commits you’ve done back
   up to the server:

 $ git push origin master

   This command works only if you cloned from a server to which you have
   write access and if nobody has pushed in the meantime. If you and someone
   else clone at the same time and they push upstream and then you push
   upstream, your push will rightly be rejected. You’ll have to fetch their
   work first and incorporate it into yours before you’ll be allowed to push.
   See Git Branching for more detailed information on how to push to remote
   servers.

  Inspecting a Remote

   If you want to see more information about a particular remote, you can use
   the git remote show <remote> command. If you run this command with a
   particular shortname, such as origin, you get something like this:

 $ git remote show origin
 * remote origin
   Fetch URL: https://github.com/schacon/ticgit
   Push  URL: https://github.com/schacon/ticgit
   HEAD branch: master
   Remote branches:
     master                               tracked
     dev-branch                           tracked
   Local branch configured for 'git pull':
     master merges with remote master
   Local ref configured for 'git push':
     master pushes to master (up to date)

   It lists the URL for the remote repository as well as the tracking branch
   information. The command helpfully tells you that if you’re on the master
   branch and you run git pull, it will automatically merge the remote’s
   master branch into the local one after it has been fetched. It also lists
   all the remote references it has pulled down.

   That is a simple example you’re likely to encounter. When you’re using Git
   more heavily, however, you may see much more information from git remote
   show:

 $ git remote show origin
 * remote origin
   URL: https://github.com/my-org/complex-project
   Fetch URL: https://github.com/my-org/complex-project
   Push  URL: https://github.com/my-org/complex-project
   HEAD branch: master
   Remote branches:
     master                           tracked
     dev-branch                       tracked
     markdown-strip                   tracked
     issue-43                         new (next fetch will store in remotes/origin)
     issue-45                         new (next fetch will store in remotes/origin)
     refs/remotes/origin/issue-11     stale (use 'git remote prune' to remove)
   Local branches configured for 'git pull':
     dev-branch merges with remote dev-branch
     master     merges with remote master
   Local refs configured for 'git push':
     dev-branch                     pushes to dev-branch                     (up to date)
     markdown-strip                 pushes to markdown-strip                 (up to date)
     master                         pushes to master                         (up to date)

   This command shows which branch is automatically pushed to when you run
   git push while on certain branches. It also shows you which remote
   branches on the server you don’t yet have, which remote branches you have
   that have been removed from the server, and multiple local branches that
   are able to merge automatically with their remote-tracking branch when you
   run git pull.

  Renaming and Removing Remotes

   You can run git remote rename to change a remote’s shortname. For
   instance, if you want to rename pb to paul, you can do so with git remote
   rename:

 $ git remote rename pb paul
 $ git remote
 origin
 paul

   It’s worth mentioning that this changes all your remote-tracking branch
   names, too. What used to be referenced at pb/master is now at paul/master.

   If you want to remove a remote for some reason — you’ve moved the server
   or are no longer using a particular mirror, or perhaps a contributor isn’t
   contributing anymore — you can either use git remote remove or git remote
   rm:

 $ git remote remove paul
 $ git remote
 origin

   Once you delete the reference to a remote this way, all remote-tracking
   branches and configuration settings associated with that remote are also
   deleted.

Tagging

   Like most VCSs, Git has the ability to tag specific points in a
   repository’s history as being important. Typically, people use this
   functionality to mark release points (v1.0, v2.0 and so on). In this
   section, you’ll learn how to list existing tags, how to create and delete
   tags, and what the different types of tags are.

  Listing Your Tags

   Listing the existing tags in Git is straightforward. Just type git tag
   (with optional -l or --list):

 $ git tag
 v1.0
 v2.0

   This command lists the tags in alphabetical order; the order in which they
   are displayed has no real importance.

   You can also search for tags that match a particular pattern. The Git
   source repo, for instance, contains more than 500 tags. If you’re
   interested only in looking at the 1.8.5 series, you can run this:

 $ git tag -l "v1.8.5*"
 v1.8.5
 v1.8.5-rc0
 v1.8.5-rc1
 v1.8.5-rc2
 v1.8.5-rc3
 v1.8.5.1
 v1.8.5.2
 v1.8.5.3
 v1.8.5.4
 v1.8.5.5

Listing tag wildcards requires -l or --list option

   If you want just the entire list of tags, running the command git tag
   implicitly assumes you want a listing and provides one; the use of -l or
   --list in this case is optional.

   If, however, you’re supplying a wildcard pattern to match tag names, the
   use of -l or --list is mandatory.

  Creating Tags

   Git supports two types of tags: lightweight and annotated.

   A lightweight tag is very much like a branch that doesn’t change — it’s
   just a pointer to a specific commit.

   Annotated tags, however, are stored as full objects in the Git database.
   They’re checksummed; contain the tagger name, email, and date; have a
   tagging message; and can be signed and verified with GNU Privacy Guard
   (GPG). It’s generally recommended that you create annotated tags so you
   can have all this information; but if you want a temporary tag or for some
   reason don’t want to keep the other information, lightweight tags are
   available too.

  Annotated Tags

   Creating an annotated tag in Git is simple. The easiest way is to specify
   -a when you run the tag command:

 $ git tag -a v1.4 -m "my version 1.4"
 $ git tag
 v0.1
 v1.3
 v1.4

   The -m specifies a tagging message, which is stored with the tag. If you
   don’t specify a message for an annotated tag, Git launches your editor so
   you can type it in.

   You can see the tag data along with the commit that was tagged by using
   the git show command:

 $ git show v1.4
 tag v1.4
 Tagger: Ben Straub <ben@straub.cc>
 Date:   Sat May 3 20:19:12 2014 -0700

 my version 1.4

 commit ca82a6dff817ec66f44342007202690a93763949
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Mon Mar 17 21:52:11 2008 -0700

     Change version number

   That shows the tagger information, the date the commit was tagged, and the
   annotation message before showing the commit information.

  Lightweight Tags

   Another way to tag commits is with a lightweight tag. This is basically
   the commit checksum stored in a file — no other information is kept. To
   create a lightweight tag, don’t supply any of the -a, -s, or -m options,
   just provide a tag name:

 $ git tag v1.4-lw
 $ git tag
 v0.1
 v1.3
 v1.4
 v1.4-lw
 v1.5

   This time, if you run git show on the tag, you don’t see the extra tag
   information. The command just shows the commit:

 $ git show v1.4-lw
 commit ca82a6dff817ec66f44342007202690a93763949
 Author: Scott Chacon <schacon@gee-mail.com>
 Date:   Mon Mar 17 21:52:11 2008 -0700

     Change version number

  Tagging Later

   You can also tag commits after you’ve moved past them. Suppose your commit
   history looks like this:

 $ git log --pretty=oneline
 15027957951b64cf874c3557a0f3547bd83b3ff6 Merge branch 'experiment'
 a6b4c97498bd301d84096da251c98a07c7723e65 Create write support
 0d52aaab4479697da7686c15f77a3d64d9165190 One more thing
 6d52a271eda8725415634dd79daabbc4d9b6008e Merge branch 'experiment'
 0b7434d86859cc7b8c3d5e1dddfed66ff742fcbc Add commit function
 4682c3261057305bdd616e23b64b0857d832627b Add todo file
 166ae0c4d3f420721acbb115cc33848dfcc2121a Create write support
 9fceb02d0ae598e95dc970b74767f19372d61af8 Update rakefile
 964f16d36dfccde844893cac5b347e7b3d44abbc Commit the todo
 8a5cbc430f1a9c3d00faaeffd07798508422908a Update readme

   Now, suppose you forgot to tag the project at v1.2, which was at the
   “Update rakefile” commit. You can add it after the fact. To tag that
   commit, you specify the commit checksum (or part of it) at the end of the
   command:

 $ git tag -a v1.2 9fceb02

   You can see that you’ve tagged the commit:

 $ git tag
 v0.1
 v1.2
 v1.3
 v1.4
 v1.4-lw
 v1.5

 $ git show v1.2
 tag v1.2
 Tagger: Scott Chacon <schacon@gee-mail.com>
 Date:   Mon Feb 9 15:32:16 2009 -0800

 version 1.2
 commit 9fceb02d0ae598e95dc970b74767f19372d61af8
 Author: Magnus Chacon <mchacon@gee-mail.com>
 Date:   Sun Apr 27 20:43:35 2008 -0700

     Update rakefile
 ...

  Sharing Tags

   By default, the git push command doesn’t transfer tags to remote servers.
   You will have to explicitly push tags to a shared server after you have
   created them. This process is just like sharing remote branches — you can
   run git push origin <tagname>.

 $ git push origin v1.5
 Counting objects: 14, done.
 Delta compression using up to 8 threads.
 Compressing objects: 100% (12/12), done.
 Writing objects: 100% (14/14), 2.05 KiB | 0 bytes/s, done.
 Total 14 (delta 3), reused 0 (delta 0)
 To git@github.com:schacon/simplegit.git
  * [new tag]         v1.5 -> v1.5

   If you have a lot of tags that you want to push up at once, you can also
   use the --tags option to the git push command. This will transfer all of
   your tags to the remote server that are not already there.

 $ git push origin --tags
 Counting objects: 1, done.
 Writing objects: 100% (1/1), 160 bytes | 0 bytes/s, done.
 Total 1 (delta 0), reused 0 (delta 0)
 To git@github.com:schacon/simplegit.git
  * [new tag]         v1.4 -> v1.4
  * [new tag]         v1.4-lw -> v1.4-lw

   Now, when someone else clones or pulls from your repository, they will get
   all your tags as well.

git push pushes both types of tags

   git push <remote> --tags will push both lightweight and annotated tags.
   There is currently no option to push only lightweight tags, but if you use
   git push <remote> --follow-tags only annotated tags will be pushed to the
   remote.

  Deleting Tags

   To delete a tag on your local repository, you can use git tag -d
   <tagname>. For example, we could remove our lightweight tag above as
   follows:

 $ git tag -d v1.4-lw
 Deleted tag 'v1.4-lw' (was e7d5add)

   Note that this does not remove the tag from any remote servers. There are
   two common variations for deleting a tag from a remote server.

   The first variation is git push <remote> :refs/tags/<tagname>:

 $ git push origin :refs/tags/v1.4-lw
 To /git@github.com:schacon/simplegit.git
  - [deleted]         v1.4-lw

   The way to interpret the above is to read it as the null value before the
   colon is being pushed to the remote tag name, effectively deleting it.

   The second (and more intuitive) way to delete a remote tag is with:

 $ git push origin --delete <tagname>

  Checking out Tags

   If you want to view the versions of files a tag is pointing to, you can do
   a git checkout of that tag, although this puts your repository in
   “detached HEAD” state, which has some ill side effects:

 $ git checkout v2.0.0
 Note: switching to 'v2.0.0'.

 You are in 'detached HEAD' state. You can look around, make experimental
 changes and commit them, and you can discard any commits you make in this
 state without impacting any branches by performing another checkout.

 If you want to create a new branch to retain commits you create, you may
 do so (now or later) by using -c with the switch command. Example:

   git switch -c <new-branch-name>

 Or undo this operation with:

   git switch -

 Turn off this advice by setting config variable advice.detachedHead to false

 HEAD is now at 99ada87... Merge pull request #89 from schacon/appendix-final

 $ git checkout v2.0-beta-0.1
 Previous HEAD position was 99ada87... Merge pull request #89 from schacon/appendix-final
 HEAD is now at df3f601... Add atlas.json and cover image

   In “detached HEAD” state, if you make changes and then create a commit,
   the tag will stay the same, but your new commit won’t belong to any branch
   and will be unreachable, except by the exact commit hash. Thus, if you
   need to make changes — say you’re fixing a bug on an older version, for
   instance — you will generally want to create a branch:

 $ git checkout -b version2 v2.0.0
 Switched to a new branch 'version2'

   If you do this and make a commit, your version2 branch will be slightly
   different than your v2.0.0 tag since it will move forward with your new
   changes, so do be careful.

Git Aliases

   Before we move on to the next chapter, we want to introduce a feature that
   can make your Git experience simpler, easier, and more familiar: aliases.
   For clarity’s sake, we won’t be using them anywhere else in this book, but
   if you go on to use Git with any regularity, aliases are something you
   should know about.

   Git doesn’t automatically infer your command if you type it in partially.
   If you don’t want to type the entire text of each of the Git commands, you
   can easily set up an alias for each command using git config. Here are a
   couple of examples you may want to set up:

 $ git config --global alias.co checkout
 $ git config --global alias.br branch
 $ git config --global alias.ci commit
 $ git config --global alias.st status

   This means that, for example, instead of typing git commit, you just need
   to type git ci. As you go on using Git, you’ll probably use other commands
   frequently as well; don’t hesitate to create new aliases.

   This technique can also be very useful in creating commands that you think
   should exist. For example, to correct the usability problem you
   encountered with unstaging a file, you can add your own unstage alias to
   Git:

 $ git config --global alias.unstage 'reset HEAD --'

   This makes the following two commands equivalent:

 $ git unstage fileA
 $ git reset HEAD -- fileA

   This seems a bit clearer. It’s also common to add a last command, like
   this:

 $ git config --global alias.last 'log -1 HEAD'

   This way, you can see the last commit easily:

 $ git last
 commit 66938dae3329c7aebe598c2246a8e6af90d04646
 Author: Josh Goebel <dreamer3@example.com>
 Date:   Tue Aug 26 19:48:51 2008 +0800

     Test for current head

     Signed-off-by: Scott Chacon <schacon@example.com>

   As you can tell, Git simply replaces the new command with whatever you
   alias it for. However, maybe you want to run an external command, rather
   than a Git subcommand. In that case, you start the command with a !
   character. This is useful if you write your own tools that work with a Git
   repository. We can demonstrate by aliasing git visual to run gitk:

 $ git config --global alias.visual '!gitk'

Summary

   At this point, you can do all the basic local Git operations — creating or
   cloning a repository, making changes, staging and committing those
   changes, and viewing the history of all the changes the repository has
   been through. Next, we’ll cover Git’s killer feature: its branching model.
