-## Chapter 2
+## Chapter 2
A tour of git: the basics
### 2.0 Copyright
-This document is a modified version originally known as "Distributed
-revision control with Mercurial" and originally authored by Bryan
-O’Sullivan. The original document was obtained from
+This document is a modified version of a document originally titled
+"Distributed revision control with Mercurial" and originally authored
+by Bryan O’Sullivan. The original document was obtained from
<http://hgbook.red-bean.com/>.
Copyright © 2006, 2007 Bryan O’Sullivan.
* Eliminate line numbers from examples
* Modified to describe git instead of mercurial
-### 2.1 Installing git on your system
+The source of this modified version can be obtained via git:
+
+ git clone git://cworth.org/git/hgbook-git
+
+or
+
+ git clone http://cworth.org/git/hgbook-git
+
+and can be [browsed online](http://git.cworth.org/git/hgbook-git)
+
+### 2.1 Installing git on your system
Prebuilt binary packages of git are available for many popular
operating systems. These make it easy to start using git on your
computer immediately.
-#### 2.1.1 Linux
+#### 2.1.1 Linux
Because each Linux distribution has its own packaging tools, policies,
and rate of development, it’s difficult to give a comprehensive set of
often git, but is sometimes git-core, (due to an unfortunate name
with git, meaning GNU Interactive Tools).
- * Debian
+ * Debian
apt-get install git-core
- * Fedora Core
+ * Fedora Core
yum install git
- * Gentoo
+ * Gentoo
- emerge git
+ emerge dev-util/git
- * OpenSUSE
+ * OpenSUSE
yum install git
- * Ubuntu
+ * Ubuntu
- apt-get install git
+ apt-get install git-core
-#### 2.1.2 Mac OS X
+#### 2.1.2 Mac OS X
A git-core package is available through
[macports](http://macports.org). Once macports is enabled, the command
port install git-core
-#### 2.1.3 Windows
+#### 2.1.3 Windows
Git has long been available as part of cygwin, and works reasonably
well in that environment. Some people find cygwin a particularly
development environment necessary to work on improving the msysgit
port of git, and WinGit, a package for installing just git itself
without the development environment, (still in Alpha as of September
-2008).
+2007).
-### 2.2 Getting started
+### 2.2 Getting started
To begin, we’ll use the “git version” command to find out whether git
is actually installed properly. Versions 1.5 and newer of git are much
yet running version 1.5 or newer, it's highly recommended that you
upgrade.
- $ git version
+ $ git version
git version 1.5.3.2
-#### 2.2.1 Built-in help
+#### 2.2.1 Built-in help
Git provides a built-in help system. This is invaluable for those
times when you find yourself stuck trying to remember how to run a
command. If you are completely stuck, simply run “git help”; it will
print a brief list of commonly-used commands, along with a description
of what each does. If you ask for help on a specific command (such as
-"git help init"), it prints more detailed information. [XXX: Does "git
-help <foo>" work universally as a built-in or does it expect man to be
-present and just call out to "man git-<foo>"?]
+"git help init"), it prints more detailed information. [XXX: Does `git
+help <foo>` work universally as a built-in or does it expect man to be
+present and just call out to `man git-<foo>`?]
[XXX: The original hgbook includes the complete output of "hg
help init" at this point. I'm not including the corresponding
available for git-<foo>? And perhaps alos provide a "git -v
help" similar to "hg -v help" for more?]
-### 2.3 Working with a repository
+### 2.3 Working with a repository
In git, everything happens inside a repository. The repository
for a project contains all of the files that “belong to” that project,
special. You can rename or delete a repository any time you like,
using either the command line or your file browser.
-#### 2.3.1 Making a local copy of a repository
+#### 2.3.1 Creating a copy of a remote repository
+
+The "git clone" command is used to create a local copy of a remote
+repository. This is generally the first git operation you will use
+when beginning to work with an existing project.
-Copying a repository is just a little bit special. While you could use
-a normal file copying command to make a copy of a repository, it’s
-best to use a built-in command that git provides. This command
-is called “git clone”, because it creates an identical copy of an
-existing repository.
+We've assembled a simple repository that will be used in the examples
+throughout this chapter. Go ahead and clone this repository now so
+that you will be able to follow along:
$ git clone git://cworth.org/git/hello
Initialized empty Git repository in /tmp/hello/.git/
repository, safe in the knowledge that it’s a private “sandbox” that
won’t affect anyone else.
-#### 2.3.2 What’s in a repository?
+#### 2.3.2 Creating copy of a local repository
+
+As mentioned above, a repository can be copied through normal
+file-copying commands. But it's useful to use "git clone" even when
+just making a local copy of a repository. Using "git clone" will be
+much faster and will use much less space than a normal copy. In fact,
+local clones are impressively fast. Go ahead and make a local clone
+now as follows:
+
+ $ git clone hello hello-clone
+ Initialized empty Git repository in /tmp/hello-clone/.git/
+ 0 blocks
+
+ [XXX Git says "empty" here, (presumably from the git-init
+ part), but shouldn't the command also report the succesful
+ clone which makes it non-empty? And what the heck does "0
+ blocks" mean? This is not friendly output.]
+
+In fact, let's make a couple more clones at the same time. This isn't
+just to drive home the speed and storage benefits of local clones, but
+we'll use each of these cloned repositories in Section 2.8 when
+discussing how to move commits between repositories:
+
+ $ git clone hello hello-pull
+ $ git clone hello hello-fetch
+ $ git clone hello hello-remote
+
+#### 2.3.2 What’s in a repository?
When we take a more detailed look inside a repository, we can see that
it contains a directory named .git. This is where git keeps all
project, while the working directory contains a snapshot of your
project at a particular point in history.
-### 2.4 A tour through history
+### 2.4 A tour through history
One of the first things we might want to do with a new, unfamiliar
-repository is understand its history. The “hg log” command gives us a
+repository is understand its history. The “git log” command gives us a
view of history.
- $ hg log
- changeset: 4:b57f9a090b62
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 15:43:07 2005 -0700
- summary: Trim comments.
+ $ git log
+ commit a1a0e8b392b17caf50325498df54802fe3c03710
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 15:43:07 2005 -0700
+
+ Trim comments.
+
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 2005 -0700
+
+ Get make to generate the final binary from a .o file.
+
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
- changeset: 3:ff5d7b70a2a9
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:58 2005 -0700
- summary: Get make to generate the final binary from a .o file.
+ Introduce a typo into hello.c.
- changeset: 2:057d3c2d823c
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:43 2005 -0700
- summary: Introduce a typo into hello.c.
+ commit 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
+ Author: Bryan O'Sullivan <mpm@selenic.com>
+ Date: Fri Aug 26 01:21:28 2005 -0700
- changeset: 1:82e55d328c8c
- user: mpm@selenic.com
- date: Fri Aug 26 01:21:28 2005 -0700
- summary: Create a makefile
+ Create a makefile
- changeset: 0:0a04b987be5a
- user: mpm@selenic.com
- date: Fri Aug 26 01:20:50 2005 -0700
- summary: Create a standard "hello, world" program
+ commit db7117a9dd9a6e57e8632ea5848e1101eee0fbde
+ Author: Bryan O'Sullivan <mpm@selenic.com>
+ Date: Fri Aug 26 01:20:50 2005 -0700
+ Create a standard "hello, world" program
+
+This command prints a record of output for each change to the project
+that was recorded. In git terminology, we call each of these recorded
+events a commit.
+
+The default fields in a record of output from “git log” are as follows.
+
+ * commit This field consists of a string of 40 hexadecimal characters.
+ This is a unique identifier for referring to particular commits.
+ * Author The identity of the person who authored the commit. This
+ field consist of two sub-fields for the user's name and email
+ address, (or at least an email-like idenitifer). Note that git
+ also stores a separate "Committer" field for the person who
+ commited the change, (since often an author will email a change to
+ a maintainer that commits it). See below for how to instruct "git
+ log" to display it as well.
+ * Date The date and time on which the commit was authored, (again
+ stored separately from the date the change was committed).
+ timezone in which it was created. (The date and time are displayed
+ in the timezone of the person who created the commit.)
+ * commit message The text message that the creator of the commit
+ entered to describe the commit, (generally a one-line summary
+ followed by more supporting text).
+
+The output of the "git log" command can be made more or less verbose
+by means of the --pretty option. For example, with "git log
+--pretty=short" the commit identifier will be omitted and only the
+first line of each commit message will be show. And with "git log
+--pretty=fuller", (the name 'fuller' is in contrast to the default
+--pretty=full), the committer name and dates will be printed in
+addition to the author name and dates.
+
+#### 2.4.1 Commits, revisions, and talking to other people
-By default, this command prints a brief paragraph of output for each
-change to the project that was recorded. In git terminology, we
-call each of these recorded events a changeset, because it can contain
-a record of changes to several files.
+As English is a notoriously sloppy language, and computer science has
+a hallowed history of terminological confusion (why use one term when
+four will do?), revision control has a variety of words and phrases
+that mean the same thing. If you are talking about git history
+with other people, you will find that what we have called a “commit”
+is often called a "revision". In other systems, a similar notion
+is referred to as a "changeset". You might even see abbreviations of
+these terms such as "rev", "change", or even "cset".
+
+While it may not matter much what word you use to refer to the concept
+of “a commit”, it's important to know how to name “a specific
+commit”. We have already seen one means of referring to a particular
+commit, the 40-character hexadecimal string shown by "git log". These
+commit identifiers are powerful because they are permanent, unique
+identifiers that always identify the same commit in any copy of a
+repository. If two users are examining a working directory associated
+with the same commit identifier, then those two users have precisely
+the same contents in all files, and exactly the same history leading
+to that commit.
+
+So there are places where it is often important to archive the
+complete commit identifier, (perhaps in bug-tracking systems to
+indicate a specific commit that fixes a bug, for example). But often,
+in more casual settings, it's more convenient to use abbreviated
+commit identifiers. Git accept any unique prefix of a commit
+identifier, (and for reasonably-sized project the first 8 or 10
+characters are almost always unique).
+
+And unlike the permanent commit identifiers, git also provides
+transient means of identifying commits. In fact, in day-to-day use of
+git, you will probably use these names more than commit
+identifiers. One example is branch names, (such as the default
+"master" branch in any git repository), or any project-specific branch
+names such as "stable", "experimental", or "crazy-insane-changes". Git
+also provides a special name "HEAD" which always refers to the current
+branch.
+
+#### 2.4.2 Naming related commits
+
+Git offers simple ways to name revisions that are related to
+particular revisions in the history. One syntax is the ~ suffix which
+refers to the parent of a commit, or if followed by a number, to the
+Nth parent. For example, since "HEAD" refers to the most recent commit
+in the current branch, "HEAD~", refers to the previous commit, and
+"HEAD~2" refers to two commits back in the history.
+
+Another useful syntax is .. which can be used to specify a range of
+commits. So "origin..master" specifies everything that has been
+committed to master since it diverged from origin.
+
+#### 2.4.3 Viewing specific revisions
+
+You can use "git log" to explore the range syntax just introduced. For
+example, to see a list of the most recent 3 revisions you can use
+"HEAD~3..", (the destination of the range is implicitly HEAD in this
+case):
+
+ $ git log HEAD~3..
+ commit a1a0e8b392b17caf50325498df54802fe3c03710
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 15:43:07 2005 -0700
+
+ Trim comments.
+
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 2005 -0700
+
+ Get make to generate the final binary from a .o file.
+
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
+
+ Introduce a typo into hello.c.
-The fields in a record of output from “hg log” are as follows.
+#### 2.4.4 Other log filters
- * changeset This field has the format of a number, followed by a
- colon, followed by a hexadecimal string. These are identifiers for
- the changeset. There are two identifiers because the number is
- shorter and easier to type than the hex string.
- * user The identity of the person who created the changeset. This is
- a free-form field, but it most often contains a person’s name and
- email address.
- * date The date and time on which the changeset was created, and the
- timezone in which it was created. (The date and time are local to
- that timezone; they display what time and date it was for the
- person who created the changeset.)
- * summary The first line of the text message that the creator of the
- changeset entered to describe the changeset.
+Besides filtering by commit identifiers, git allows you to easily
+filter the log output according to which files (or directories) are
+modified by listing them after "--" which is necessary to distinguish
+commit names from file names:
-The default output printed by “hg log” is purely a summary; it is
-missing a lot of detail.
+ $ git log -- Makefile
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 2005 -0700
+
+ Get make to generate the final binary from a .o file.
+
+ commit 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
+ Author: Bryan O'Sullivan <mpm@selenic.com>
+ Date: Fri Aug 26 01:21:28 2005 -0700
+
+ Create a makefile
-Figure [2.1][8] provides a graphical representation of the history of
-the hello repository, to make it a little easier to see which
-direction history is “flowing” in. We’ll be returning to this figure
-several times in this chapter and the chapter that follows.
+And "git log" can also filter based on the dates at which commits were
+created:
-* * *
+ $ git log --since="2 weeks ago" --until="yesterday"
-![PIC][9]
+ [XXX: By default, "git log" displays author dates as "Date"
+ but then uses commit dates when given a --since option. That
+ seems like broken defaults to me. Why the inconsistency?]
-Figure 2.1:
-Graphical history of the hello repository
+Another useful option is -n or --max-count which, unsurprisingly,
+limits the maximum number of commits to be displayed.
-* * *
+#### 2.4.5 More detailed information
-#### 2.4.1 Changesets, revisions, and talking to other people
+While the default information printed by “git log” is useful if you
+already know what you’re looking for, you may need to see more details
+of the change, such as the "diffstat" information with --stat:
-As English is a notoriously sloppy language, and computer science has
-a hallowed history of terminological confusion (why use one term when
-four will do?), revision control has a variety of words and phrases
-that mean the same thing. If you are talking about Mercurial history
-with other people, you will find that the word “changeset” is often
-compressed to “change” or (when written) “cset”, and sometimes a
-changeset is referred to as a “revision” or a “rev”.
-
-While it doesn’t matter what word you use to refer to the concept of
-“a changeset”, the identifier that you use to refer to “a specific
-changeset” is of great importance. Recall that the changeset field in
-the output from “hg log” identifies a changeset using both a number
-and a hexadecimal string.
-
- * The revision number is only valid in that repository,
- * while the hex string is the permanent, unchanging identifier that
- will always identify that exact changeset in every copy of the
- repository.
-
-This distinction is important. If you send someone an email talking
-about “revision 33”, there’s a high likelihood that their revision 33
-will not be the same as yours. The reason for this is that a revision
-number depends on the order in which changes arrived in a repository,
-and there is no guarantee that the same changes will happen in the
-same order in different repositories. Three changes a,b,c can easily
-appear in one repository as 0,1,2, while in another as 1,0,2.
-
-Mercurial uses revision numbers purely as a convenient shorthand. If
-you need to discuss a changeset with someone, or make a record of a
-changeset for some other reason (for example, in a bug report), use
-the hexadecimal identifier.
-
-#### 2.4.2 Viewing specific revisions
-
-To narrow the output of “hg log” down to a single revision, use the -r
-(or --rev) option. You can use either a revision number or a long-form
-changeset identifier, and you can provide as many revisions as you
-want.
-
- $ hg log -r 3
- changeset: 3:ff5d7b70a2a9
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:58 2005 -0700
- summary: Get make to generate the final binary from a .o file.
-
- $ hg log -r ff5d7b70a2a9
- changeset: 3:ff5d7b70a2a9
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:58 2005 -0700
- summary: Get make to generate the final binary from a .o file.
+ $ git log --stat --max-count=3
+ commit a1a0e8b392b17caf50325498df54802fe3c03710
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 15:43:07 2005 -0700
- $ hg log -r 1 -r 4
- changeset: 1:82e55d328c8c
- user: mpm@selenic.com
- date: Fri Aug 26 01:21:28 2005 -0700
- summary: Create a makefile
+ Trim comments.
- changeset: 4:b57f9a090b62
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 15:43:07 2005 -0700
- summary: Trim comments.
+ hello.c | 8 ++------
+ 1 files changed, 2 insertions(+), 6 deletions(-)
-
-If you want to see the history of several revisions without having to
-list each one, you can use range notation; this lets you express the
-idea “I want all revisions between a and b, inclusive”.
-
- $ hg log -r 2:4
- changeset: 2:057d3c2d823c
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:43 2005 -0700
- summary: Introduce a typo into hello.c.
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 2005 -0700
- changeset: 3:ff5d7b70a2a9
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:58 2005 -0700
- summary: Get make to generate the final binary from a .o file.
+ Get make to generate the final binary from a .o file.
- changeset: 4:b57f9a090b62
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 15:43:07 2005 -0700
- summary: Trim comments.
+ Makefile | 2 ++
+ 1 files changed, 2 insertions(+), 0 deletions(-)
-
-Mercurial also honours the order in which you specify revisions, so
-“hg log -r 2:4” prints 2,3,4 while “hg log -r 4:2” prints 4,3,2.
-
-#### 2.4.3 More detailed information
-
-While the summary information printed by “hg log” is useful if you
-already know what you’re looking for, you may need to see a complete
-description of the change, or a list of the files changed, if you’re
-trying to decide whether a changeset is the one you’re looking
-for. The “hg log” command’s -v (or --verbose) option gives you this
-extra detail.
-
- $ hg log -v -r 3
- changeset: 3:ff5d7b70a2a9
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:58 2005 -0700
- files: Makefile
- description:
- Get make to generate the final binary from a .o file.
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
+ Introduce a typo into hello.c.
-
-If you want to see both the description and content of a change, add
-the -p (or --patch) option. This displays the content of a change as a
-unified diff (if you’ve never seen a unified diff before, see
-section [12.4][10] for an overview).
-
- $ hg log -v -p -r 2
- changeset: 2:057d3c2d823c
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:43 2005 -0700
- files: hello.c
- description:
- Introduce a typo into hello.c.
+ hello.c | 2 +-
+ 1 files changed, 1 insertions(+), 1 deletions(-)
+
+Or perhaps you'd like to see the actual patch content of each change,
+which you can get with -p. That commit with the word typo in its name
+looks suspicous, so let's tak a closer look. Remember that we can name
+it as master~3, HEAD~3, or any prefix of its commit identifier, (such
+as 13ed136b):
+
+ $ git log -p -n 1 13ed136b
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
+ Introduce a typo into hello.c.
- diff -r 82e55d328c8c -r 057d3c2d823c hello.c
- --- a/hello.c Fri Aug 26 01:21:28 2005 -0700
- +++ b/hello.c Tue Sep 06 13:15:43 2005 -0700
- @@ -11,6 +11,6 @@
+ diff --git a/hello.c b/hello.c
+ index ed55ec0..80b260c 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -11,6 +11,6 @@
+
+ int main(int argc, char **argv)
+ {
+ - printf("hello, world!\n");
+ + printf("hello, world!\");
+ return 0;
+ }
+
+Of course, wanting to see all this information for a single commit is
+such a common operation that it's given its own name in git, "git
+show". So "git show 13ed136b" is a much easier way to get exactly the
+same output:
+
+ $ git show 13ed136b
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
- int main(int argc, char ⋆⋆argv)
- {
- - printf("hello, world!∖n");
- + printf("hello, world!∖");
- return 0;
- }
+ Introduce a typo into hello.c.
-
-### 2.5 All about command options
-
-Let’s take a brief break from exploring Mercurial commands to discuss
+ diff --git a/hello.c b/hello.c
+ index ed55ec0..80b260c 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -11,6 +11,6 @@
+
+ int main(int argc, char **argv)
+ {
+ - printf("hello, world!\n");
+ + printf("hello, world!\");
+ return 0;
+ }
+
+### 2.5 All about command options
+
+Let’s take a brief break from exploring git commands to discuss
a pattern in the way that they work; you may find this useful to keep
in mind as we continue our tour.
-Mercurial has a consistent and straightforward approach to dealing
+Git has a consistent and straightforward approach to dealing
with the options that you can pass to commands. It follows the
conventions for options that are common to modern Linux and Unix
systems.
- * Every option has a long name. For example, as we’ve already seen,
- the “hg log” command accepts a --rev option.
- * Most options have short names, too. Instead of --rev, we can use
- -r. (The reason that some options don’t have short names is that
- the options in question are rarely used.)
- * Long options start with two dashes (e.g. --rev), while short
- options start with one (e.g. -r).
+ * Most options have long names. For example, as we’ve already seen,
+ the “git log" command accepts a `--max-count=<number>` option.
+ * Some options have short, single-character names. Often these are
+ aliases for long commands, (such as `-n <number>` instead of
+ `--max-count=<number>`), but sometimes the option exists in
+ short-form with no long-form equivalent, (such as `-p`). [XXX: It
+ wouldn't hurt to fix this by adding `--patch`, etc. right?]
+ * Long options start with two dashes (e.g. `--max-count`), while short
+ options start with one (e.g. `-n`).
+
* Option naming and usage is consistent across commands. For
- example, every command that lets you specify a changeset ID or
- revision number accepts both -r and --rev arguments.
-
-In the examples throughout this book, I use short options instead of
-long. This just reflects my own preference, so don’t read anything
-significant into it.
-
-Most commands that print output of some kind will print more output
-when passed a -v (or --verbose) option, and less when passed -q (or
---quiet).
-
-### 2.6 Making and reviewing changes
-
-Now that we have a grasp of viewing history in Mercurial, let’s take a
-look at making some changes and examining them.
-
-The first thing we’ll do is isolate our experiment in a repository of
-its own. We use the “hg clone” command, but we don’t need to clone a
-copy of the remote repository. Since we already have a copy of it
-locally, we can just clone that instead. This is much faster than
-cloning over the network, and cloning a local repository uses less
-disk space in most cases, too.
-
- $ cd ..
- $ hg clone hello my-hello
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
- $ cd my-hello
-
-As an aside, it’s often good practice to keep a “pristine” copy of a
-remote repository around, which you can then make temporary clones of
-to create sandboxes for each task you want to work on. This lets you
-work on multiple tasks in parallel, each isolated from the others
-until it’s complete and you’re ready to integrate it back. Because
-local clones are so cheap, there’s almost no overhead to cloning and
-destroying repositories whenever you want.
-
-In our my-hello repository, we have a file hello.c that contains the
-classic “hello, world” program. Let’s use the ancient and venerable
-sed command to edit this file so that it prints a second line of
-output. (I’m only using sed to do this because it’s easy to write a
-scripted example this way. Since you’re not under the same constraint,
-you probably won’t want to use sed; simply use your preferred text
-editor to do the same thing.)
-
- $ sed -i '/printf/a∖∖tprintf("hello again!∖∖n");' hello.c
-
-Mercurial’s “hg status” command will tell us what Mercurial knows
-about the files in the repository.
-
- $ ls
- Makefile hello.c
- $ hg status
- M hello.c
-
-The “hg status” command prints no output for some files, but a line
-starting with “M” for hello.c. Unless you tell it to, “hg status” will
-not print any output for files that have not been modified.
-
-The “M” indicates that Mercurial has noticed that we modified
-hello.c. We didn’t need to inform Mercurial that we were going to
-modify the file before we started, or that we had modified the file
-after we were done; it was able to figure this out itself.
+ example, every command that lets you specify a commit identifier
+ or range will accept the same expressions, (HEAD~3,
+ origin..master, 72d4f10e, etc), while any command that can be
+ limited by paths will accept the same expressions ("-- doc/
+ some-file.c"), etc.
+
+Many commands that print output of some kind can be made more quiet by
+passing the -q or --quiet options.
+
+### 2.6 Making and reviewing changes
+
+Now that we have a grasp of viewing history in git, let’s take a look
+at making some changes and examining them. You should be working
+within the "hello" directory that we originally cloned.
+
+In the repository, we have a file hello.c that contains the classic
+“hello, world” program. But this program currently has a syntax error
+and won't compile, (there's a missing 'n' between the '\' and the '"'
+on the line containing printf). Let's fix that now. You can use a text
+editor to correct the file, or you can copy-and-paste the sed command
+below:
+
+ $ sed -i '/printf/s/\\"/\\n"/' hello.c
+
+After you've made that change, the “git status” command will tell you
+what git knows about the files in the repository.
+
+ $ ls
+ hello.c Makefile
+ $ git status
+ # On branch master
+ # Changed but not updated:
+ # (use "git add <file>..." to update what will be committed)
+ #
+ # modified: hello.c
+ #
+ no changes added to commit (use "git add" and/or "git commit -a")
+
+First "git status" tells us that the current branch is "master". This
+means that the master branch is what will be updated when we create a
+new commit.
+
+Note: In git a branch is a very simple notion---it's simply a name
+that points to a particular commit, (literally nothing more than a
+pointer---look at the contents of .git/refs/heads/master if you're
+curious). The fact that a branch is so light is what makes the
+creation of new branches an instantaneous operation in git. Together
+with the ease of merging, git makes branches a joy to work with. But
+we'll delay talk of branching and merging to a future chapter.
+
+Next “git status” prints a line with "modified" for each modified
+file---in this case just hello.c. The “git status” command will not
+print any output for files that have not been modified.
+
+Notice that we didn’t need to inform git that we were going to modify
+the file before we started, or that we had modified the file after we
+were done; it was able to figure this out itself.
It’s a little bit helpful to know that we’ve modified hello.c, but we
might prefer to know exactly what changes we’ve made to it. To do
-this, we use the “hg diff” command.
-
- $ hg diff
- diff -r b57f9a090b62 hello.c
- --- a/hello.c Tue Sep 06 15:43:07 2005 -0700
- +++ b/hello.c Sun Jun 17 18:05:50 2007 +0000
- @@ -8,5 +8,6 @@ int main(int argc, char ⋆⋆argv)
- int main(int argc, char ⋆⋆argv)
- {
- printf("hello, world!∖");
- + printf("hello again!∖n");
- return 0;
- }
-
-### 2.7 Recording changes in a new changeset
-
-We can modify files, build and test our changes, and use “hg status”
-and “hg diff” to review our changes, until we’re satisfied with what
+this, we use the “git diff” command.
+
+ $ git diff
+ diff --git a/hello.c b/hello.c
+ index 9a3ff79..ea364d3 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -7,6 +7,6 @@
+
+ int main(int argc, char **argv)
+ {
+ - printf("hello, world!\");
+ + printf("hello, world!\n");
+ return 0;
+ }
+
+### 2.7 Recording changes in a new commit
+
+We can modify files, build and test our changes, and use “git status”
+and “git diff” to review our changes, until we’re satisfied with what
we’ve done and arrive at a natural stopping point where we want to
-record our work in a new changeset.
-
-The “hg commit” command lets us create a new changeset; we’ll usually
-refer to this as “making a commit” or “committing”.
-
-#### 2.7.1 Setting up a username
-
-When you try to run “hg commit” for the first time, it is not
-guaranteed to succeed. Mercurial records your name and address with
-each change that you commit, so that you and others will later be able
-to tell who made each change. Mercurial tries to automatically figure
-out a sensible username to commit the change with. It will attempt
-each of the following methods, in order:
-
- 1. If you specify a -u option to the “hg commit” command on the
- command line, followed by a username, this is always given the
- highest precedence.
- 2. If you have set the HGUSER environment variable, this is checked next.
- 3. If you create a file in your home directory called .hgrc, with a
- username entry, that will be used next. To see what the contents
- of this file should look like, refer to section [2.7.1][11]
- below.
- 4. If you have set the EMAIL environment variable, this will be used
- next.
- 5. Mercurial will query your system to find out your local user name
- and host name, and construct a username from these
- components. Since this often results in a username that is not
- very useful, it will print a warning if it has to do this.
-
-If all of these mechanisms fail, Mercurial will fail, printing an
-error message. In this case, it will not let you commit until you set
-up a username.
-
-You should think of the HGUSER environment variable and the -u option
-to the “hg commit” command as ways to override Mercurial’s default
-selection of username. For normal use, the simplest and most robust
-way to set a username for yourself is by creating a .hgrc file; see
-below for details.
-
-##### Creating a Mercurial configuration file
-
-To set a user name, use your favourite editor to create a file called
-.hgrc in your home directory. Mercurial will use this file to look up
-your personalised configuration settings. The initial contents of your
-.hgrc should look like this.
-
- # This is a Mercurial configuration file.
- [ui]
- username = Firstname Lastname <email.address@domain.net>
-
-The “[ui]” line begins a section of the config file, so you can read
-the “username = ...” line as meaning “set the value of the username
-item in the ui section”. A section continues until a new section
-begins, or the end of the file. Mercurial ignores empty lines and
-treats any text from “#” to the end of a line as a comment.
-
-##### Choosing a user name
-
-You can use any text you like as the value of the username config
-item, since this information is for reading by other people, but for
-interpreting by Mercurial. The convention that most people follow is
-to use their name and email address, as in the example above.
-
-Note: Mercurial’s built-in web server obfuscates email addresses, to
-make it more difficult for the email harvesting tools that spammers
-use. This reduces the likelihood that you’ll start receiving more junk
-email if you publish a Mercurial repository on the web.
-
-#### 2.7.2 Writing a commit message
-
-When we commit a change, Mercurial drops us into a text editor, to
+record our work in a new commit.
+
+If you'd like, go ahead and build the program now with "make" and run
+it to ensure it works. Everything should look good so we're just about
+ready to make a commit. Unsurprisingly, we'll be using "git commit" to
+do this.
+
+#### 2.7.1 Introducing yourself to git
+
+Before you run "git commit" though, you should introduce yourself to
+git. Git records your name and email address with each change that
+you commit, (as both author and committer unless you tell it
+otherwise), so that you and others will later be able to tell who made
+each change.
+
+Git tries to automatically figure out a sensible name and address to
+attribute to both author and committer if you haven't explicitly told
+it a name and address. And it tries a lot, (detailed below). If you're
+not interested in these details, you might want to skip to the next
+section which explains how to avoid all this guesswork and tell git
+what your name and email address are.
+
+Here is a list of all the guessing that git will attempt. It will
+attempt each of the following methods, in order, (stopping for each of
+the author and committer name and email as soon as a value is found):
+
+ 1. If you specify a --author option to the “git commit” command on
+ the command line, followed by a `"Real Name <email@example.com>"`
+ string, then this name and addresss will be used for the author
+ fields. The committer fields will still be determined as
+ below. This option is very helpful for when applying a commit
+ originally authored by someone other than yourself.
+ 2. If any of the `GIT_AUTHOR_NAME`, `GIT_AUTHOR_EMAIL`,
+ `GIT_COMMITTER`_NAME, or `GIT_COMMITER_EMAIL` environment variables
+ are set, then those values will be used for the corresponding
+ fields.
+ 3. If you have a file in your home directory called .gitconfig, with
+ name or email settings in the [user] section, then these values
+ will be used to set any remaining author and committer
+ fields. For more details on the contents of this file, refer to
+ section 2.7.1 below.
+ 4. If you have a file in the local repository called .git/config,
+ again with name or email settings in the [user] section, then
+ these values will be used to set any remaining author and
+ committer fields.
+ 5. If you have set the `EMAIL` environment variable, this will be used
+ to set author and committer email addresses if still unset.
+ 6. git will query your system to find out your real name from
+ available GECOS field and your username, hostname, and domain to
+ construct an email address, (or at least an identifier resembling
+ an email address).
+
+If all of these mechanisms fail, "git commit" will fail, printing an
+error message instructing you how to use "git config" to tell git your
+name and email address.
+
+You should think of the `GIT_AUTHOR`/`COMMITER_NAME`/`EMAIL` environment
+variables and the --author option to the “git commit” command as ways
+to override git’s default selection. For normal use, the simplest and
+most robust way to set your information is by creating a .gitconfig
+file, (either manually or with the "git config" command); see below
+for details.
+
+##### Creating a git configuration file
+
+To set your name and email address, just use the following commands:
+
+ git config --global user.name "Your Name"
+ git config --global user.email "you@example.com"
+
+The --global option means that this command will set global
+information, (affecting all repositories on this machine), in the
+.gitconfig file in your home directory. Alternately, you could omit
+the --global which would make the change take effect only in the local
+repository. This is convenient if you want to have different email
+addresses associated with different projects, for example.
+
+Of course, git's configuration file is a simple-to-edit plain-text
+file, so instead of using the above commands, you can also just edit
+the files directly. Use your favorite editor to create a file called
+.gitconfig in your home directory, (or if you ran the above commands
+then it will be there already). The initial contents of your
+.gitconfig should look like this.
+
+ # This is a git configuration file.
+ [user]
+ name = Your Name
+ email = you@example.com
+
+Similarly, you can make a repository-specific configuration by editing
+.git/config in the local repository. It will already have some
+sections present, (created by the "git clone"), just add a [user]
+section as above.
+
+The “[user]” line begins a section of the config file, so you can read
+the “name = ...” line as meaning “set the value of the name item in
+the user section”. This is the same notion expressed with the
+"user.name" syntax on the git-config command line. A section
+continues until a new section begins, or the end of the file. Git
+ignores empty lines and treats any text from “#” to the end of a line
+as a comment.
+
+##### Choosing your name and email
+
+You can use any text you like as the value of the name and email
+configuration items, since this information is for reading by other
+people, not for interpreting by git. It is conventional to use your
+actual name as well as a valid email address. But some people, (notably
+Linus Torvalds, the original author of git), actually like the default
+username@hostname convention that git falls back on without any
+additional information about an email address. There's no requirement
+that the email address actually be valid, and perhaps it's useful to
+be reminded which machine was used to create particular commits. So
+choose the name and email you wish, or follow a particular project's
+conventions.
+
+#### 2.7.2 Writing a commit message
+
+When we commit a change, git drops us into a text editor to
enter a message that will describe the modifications we’ve made in
-this changeset. This is called the commit message. It will be a record
-for readers of what we did and why, and it will be printed by “hg log”
+this commit. This is called the commit message. It will be a record
+for readers of what we did and why, and it will be printed by “git log”
after we’ve finished committing.
- $ hg commit
-
-The editor that the “hg commit” command drops us into will contain an
-empty line, followed by a number of lines starting with “HG:”.
+ $ git commit -a
+
+Note: The -a on the command-line instructs git to commit the new
+content of *all* tracked files that have been modified. This is a
+convenience over explicitly listing filenames to be committed on the
+`git commit` command line. It is useful to use `git commit <files>`
+when there is a need to commit only some subset of the files that have
+been modified.
+
+If new files need to be committed for the first time, just use `git
+add <file>` before `git commit -a`. If a file needs to be removed,
+just remove it as normal before committing and `git commit -a` will
+notice that---it does not need to be explicitly told about the
+removal.
+
+The editor that the `git commit` command drops us into will contain an
+empty line, followed by a number of lines starting with “#”. These
+lines contain the same information as seen in `git status` before:
+
+ empty line
+ # Please enter the commit message for your changes.
+ # (Comment lines starting with '#' will not be included)
+ # On branch master
+ # Changes to be committed:
+ # (use "git reset HEAD <file>..." to unstage)
+ #
+ # modified: hello.c
+ #
+ # Untracked files:
+ # (use "git add <file>..." to include in what will be committed)
+ #
+ # hello
+ # hello.o
+
+Notice that two untracked files (hello and hello.o) have now appeared
+from the build process. Git is reminding us of these in case we
+intended to commit them as well, (in which case we would need to "git
+add" them). We don't actually want to commit these files so we will
+ignore them for now, (and we could tell git to ignore them as well by
+listing them in a .gitignore file).
+
+Git will ignore all lines in the commit message that start with “#”;
+it uses them only to give us information on the commit. Modifying or
+deleting these lines has no effect.
- empty line
- HG: changed hello.c
+#### 2.7.3 Writing a good commit message
-Mercurial ignores the lines that start with “HG:”; it uses them only
-to tell us which files it’s recording changes to. Modifying or
-deleting these lines has no effect.
+A good commit message will generally have a single line that
+summarizes the commit, a blank line, and then one or more pargraphs
+with supporting detail. Since many tools only print the first line of
+a commit message by default, it’s important that the first line stands
+alone.
-#### 2.7.3 Writing a good commit message
+One example of a first-line-only viewer is "git log
+--pretty=short". Other examples include graphical history viewers such
+as gitk and gitview, and web-based viewers such as gitweb and cgit.
-Since “hg log” only prints the first line of a commit message by
-default, it’s best to write a commit message whose first line stands
-alone. Here’s a real example of a commit message that doesn’t follow
+Here’s a real example of a commit message that doesn’t follow
this guideline, and hence has a summary that is not readable.
- changeset: 73:584af0e231be
- user: Censored Person <censored.person@example.org>
- date: Tue Sep 26 21:37:07 2006 -0700
- summary: include buildmeister/commondefs. Add an exports and install
+ $ git log --pretty=short
+ commit 3ef5535144da88a854f7930503845cd44506c2e2
+ Author: Censored Person <censored.person@example.org>
+
+ include buildmeister/commondefs. Add an exports and install
As far as the remainder of the contents of the commit message are
-concerned, there are no hard-and-fast rules. Mercurial itself doesn’t
+concerned, there are no hard-and-fast rules. git itself doesn’t
interpret or care about the contents of the commit message, though
your project may have policies that dictate a certain kind of
formatting.
My personal preference is for short, but informative, commit messages
that tell me something that I can’t figure out with a quick glance at
-the output of “hg log --patch”.
+the output of "git log --stat" or “git log -p", (so repeating the list
+of all modified files is not useful, for example).
-#### 2.7.4 Aborting a commit
+#### 2.7.4 Aborting a commit
If you decide that you don’t want to commit while in the middle of
editing a commit message, simply exit from your editor without saving
the file that it’s editing. This will cause nothing to happen to
either the repository or the working directory.
-If we run the “hg commit” command without any arguments, it records
-all of the changes we’ve made, as reported by “hg status” and “hg
-diff”.
-
-#### 2.7.5 Admiring our new handiwork
-
-Once we’ve finished the commit, we can use the “hg tip” command to
-display the changeset we just created. This command produces output
-that is identical to “hg log”, but it only displays the newest
-revision in the repository.
-
- $ hg tip -vp
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- files: hello.c
- description:
- Added an extra line of output
+#### 2.7.5 Admiring our new handiwork
+
+Once we’ve finished the commit, we can use the “git show” command to
+display the commit we just created. As discussed previously, this
+command produces output that is identical to “git log -p”, but for
+only a single revision, (and the most recent revision by default):
+
+ $ git show
+ commit fd21e5d6c5eedee70137229ebf348c25181812ab
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Fri Sep 28 12:50:16 2007 -0700
+
+ Fixed the typo so the program actuall complies now.
+ diff --git a/hello.c b/hello.c
+ index 9a3ff79..ea364d3 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -7,6 +7,6 @@
+
+ int main(int argc, char **argv)
+ {
+ - printf("hello, world!\");
+ + printf("hello, world!\n");
+ return 0;
+ }
+
+Note that you will not see the same commit identifier for your commit,
+even if the change you made is identical to mine. The commit
+identifier incorporates not only the contents of the files, but commit
+message, the author and committer names and emails, and the author and
+commit dates. (OK, so now you probably know enough to be able to guess
+the right command to produce a commit with exactly the commit
+identifier shown above. Can you do it?)
+
+#### 2.7.6 Fixing up a broken commit (before anyone else sees it)
+
+So now that we've cloned a local repository, made a change to the
+code, setup our name and email address, and made a careful commit,
+we're just about ready to share our change with the world. But wait,
+that commit message has some really embarrassing misspellings in
+it. Wouldn't it be nice to touch those up before I post this commit
+with a never-to-be-changed again commit identifier?
+
+This is the exact situation for which "git commit --amend" was
+invented. So I can just run that now and fix the broken commit
+message:
+
+ $ git commit --amend
+
+Here's the final result:
+
+ $ git show
+ commit 3c54ac672ec1130b36837f1b708054a7a1d402de
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Fri Sep 28 12:50:16 2007 -0700
- diff -r b57f9a090b62 -r fa1321bf0c80 hello.c
- --- a/hello.c Tue Sep 06 15:43:07 2005 -0700
- +++ b/hello.c Sun Jun 17 18:05:50 2007 +0000
- @@ -8,5 +8,6 @@ int main(int argc, char ⋆⋆argv)
- int main(int argc, char ⋆⋆argv)
- {
- printf("hello, world!∖");
- + printf("hello again!∖n");
- return 0;
- }
+ Fixed the typo so the program actually compiles now.
+ diff --git a/hello.c b/hello.c
+ index 9a3ff79..ea364d3 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -7,6 +7,6 @@
+
+ int main(int argc, char **argv)
+ {
+ - printf("hello, world!\");
+ + printf("hello, world!\n");
+ return 0;
+ }
+
+Note that we didn't use "commit -a" this time. This means that "git
+commit --amend" will amend only the commit message and not any of the
+actual files being tracked, (even if some of them had been modified
+between the commits).
+
+It's also possible to use "git commit -a --amend" to similarly fix up
+mistakes noticed in code. That will replace the most recent commit
+with a different commit based on any new changes to files.
+
+I do feel a little hesitant to mention "git commit -a --amend". It's a
+handy command for fixing up something like a misspelling in a comment
+in the code. But if there is anything more significant than that, then
+it would generally be better to create an additional commit rather
+than amending an existing commit. This is important for several
+reasons:
+
+ * The amend operation will destroy a state that was previously saved
+ in a commit. If it's just the commit message being changed, then
+ that's no big deal. But if the contents are being amended, then a
+ mistake could eliminate something valuable.
+
+ * All commits should be logically independent and as small as
+ possible. Abusing "git commit -a --amend" can cause a small commit
+ to grow and acquire unrelated changes.
+
+It's worth emphasizing the value of minimal, independent commits. The
+smaller the changes are the more useful the history will be when
+actually using the history, not just viewing it. This is particularly
+important when doing "git bisect"---that's a powerful tool for
+isolating a single commit that introduces a bug. And it's much more
+helpful when the commit it isolates is as small as possible.
+
+One advantage of using git over some other systems is that the commit
+speed is blazingly fast. The tool doesn't punish you at all for
+committing as often as you get our project into a state that is worth
+saving. "Commit early, commit often" is a well-supported mode of
+operation with git.
+
+### 2.8 Sharing changes
+
+We mentioned earlier that repositories in git are
+self-contained. This means that the commit we just created exists
+only in our hello repository. Let’s look at a few ways that we can
+propagate this change into other repositories.
-We refer to the newest revision in the repository as the tip revision,
-or simply the tip.
+#### 2.8.1 Pulling changes from the original repository
-### 2.8 Sharing changes
+Recall that in Section 2.3.2 we made several local clones of the hello
+repository before we made any commits. This allows us to simulate what
+happens when upstream changes have been committed after you originally
+cloned.
-We mentioned earlier that repositories in Mercurial are
-self-contained. This means that the changeset we just created exists
-only in our my-hello repository. Let’s look at a few ways that we can
-propagate this change into other repositories.
+The simplest, (and quite common), scenario is that you inherently
+trust any changes in the original repository and you want to pull
+these directly into your clone. This might be the case if you are
+using git simply to track the progress of a project without making any
+changes.
-#### 2.8.1 Pulling changes from another repository
-
-To get started, let’s clone our original hello repository, which does
-not contain the change we just committed. We’ll call our temporary
-repository hello-pull.
-
- $ cd ..
- $ hg clone hello hello-pull
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-
-We’ll use the “hg pull” command to bring changes from my-hello into
-hello-pull. However, blindly pulling unknown changes into a repository
-is a somewhat scary prospect. Mercurial provides the “hg incoming”
-command to tell us what changes the “hg pull” command would pull into
-the repository, without actually pulling the changes in.
-
- $ cd hello-pull
- $ hg incoming ../my-hello
- comparing with ../my-hello
- searching for changes
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
+In this case, the operation is as simple as just calling "git pull":
+
+ $ cd ../hello-pull
+ $ git pull
+ remote: Generating pack...
+ Unpacking 3 objects...
+ 100% (3/3) done
+ remote: Done counting 5 objects.
+ Result has 3 objects.
+ Deltifying 3 objects...
+ 100% remote: (3/3) done
+ Total 3 (delta 1), reused 0 (delta 0)
+ * refs/remotes/origin/master: fast forward to branch 'master' of /tmp/hello
+ old..new: a1a0e8b..3c54ac6
+ Updating a1a0e8b..3c54ac6
+ Fast forward
+ hello.c | 2 +-
+ 1 files changed, 1 insertions(+), 1 deletions(-)
+
+XXX: Git is fairly noisy here, but a user has little need to care
+about the several stages of operation involved here. As a tutorial
+writer I'd like to say "ignore all that progress stuff, and look at
+where the stat information starts" but it's hard for a new user to
+even be able to understand that. I think it would be ideal if all of
+the progress-tracking spew were reduced to a single line. Something
+like "Computing (100%) Transferring (100%)" or whatever.
+
+After (lots!) of progresss indication, git gives a report of which
+files were modified, (which is very useful for getting a quick feel
+for what happened). If you would like more details on what changes
+came in, git provides a range that is perfect for examining. Let's
+take a look (again, the commit identifiers will be different for you
+--- just copy-and-paste the range that git prints):
+
+ $ git log a1a0e8b..3c54ac6
+ commit 3c54ac672ec1130b36837f1b708054a7a1d402de
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Fri Sep 28 12:50:16 2007 -0700
+ Fixed the typo so the program actually compiles now.
-(Of course, someone could cause more changesets to appear in the
-repository that we ran “hg incoming” in, before we get a chance to “hg
-pull” the changes, so that we could end up pulling changes that we
-didn’t expect.)
+As expected, we received just the one commit.
-Bringing changes into a repository is a simple matter of running the
-“hg pull” command, and telling it which repository to pull from.
+So that's all that's needed in the common case. Just run "git pull"
+everytime you want to pull in new changes that have landed in the
+upstream repository.
- $ hg tip
- changeset: 4:b57f9a090b62
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 15:43:07 2005 -0700
- summary: Trim comments.
-
- $ hg pull ../my-hello
- pulling from ../my-hello
- searching for changes
- adding changesets
- adding manifests
- adding file changes
- added 1 changesets with 1 changes to 1 files
- (run 'hg update' to get a working copy)
- $ hg tip
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
+Note: Mercurial users who are reading this might wonder if there's a
+need for the equivalent of "hg update" after doing a "git pull". And
+the answer is no. Unlike mercurial, "git pull", (and "git merge") will
+automatically update the working-directory files as necessary.
-As you can see from the before-and-after output of “hg tip”, we have
-successfully pulled changes into our repository. There remains one
-step before we can see these changes in the working directory.
-
-#### 2.8.2 Updating the working directory
-
-We have so far glossed over the relationship between a repository and
-its working directory. The “hg pull” command that we ran in
-section [2.8.1][12] brought changes into the repository, but if we
-check, there’s no sign of those changes in the working directory. This
-is because “hg pull” does not (by default) touch the working
-directory. Instead, we use the “hg update” command to do this.
-
- $ grep printf hello.c
- printf("hello, world!∖");
- $ hg update tip
- 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
- $ grep printf hello.c
- printf("hello, world!∖");
- printf("hello again!∖n");
-
-It might seem a bit strange that “hg pull” doesn’t update the working
-directory automatically. There’s actually a good reason for this: you
-can use “hg update” to update the working directory to the state it
-was in at any revision in the history of the repository. If you had
-the working directory updated to an old revision—to hunt down the
-origin of a bug, say—and ran a “hg pull” which automatically updated
-the working directory to a new revision, you might not be terribly
-happy.
-
-However, since pull-then-update is such a common thing to do,
-Mercurial lets you combine the two by passing the -u option to “hg
-pull”.
-
- hg pull -u
-
-If you look back at the output of “hg pull” in section [2.8.1][12]
-when we ran it without -u, you can see that it printed a helpful
-reminder that we’d have to take an explicit step to update the working
-directory:
-
- (run 'hg update' to get a working copy)
-
-To find out what revision the working directory is at, use the “hg
-parents” command.
-
- $ hg parents
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
-
-If you look back at figure [2.1][8], you’ll see arrows connecting each
-changeset. The node that the arrow leads from in each case is a
-parent, and the node that the arrow leads to is its child. The working
-directory has a parent in just the same way; this is the changeset
-that the working directory currently contains.
-
-To update the working directory to a particular revision, give a
-revision number or changeset ID to the “hg update” command.
-
- $ hg update 2
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
- $ hg parents
- changeset: 2:057d3c2d823c
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:43 2005 -0700
- summary: Introduce a typo into hello.c.
-
- $ hg update
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-
-If you omit an explicit revision, “hg update” will update to the tip
-revision, as shown by the second call to “hg update” in the example
-above.
-
-#### 2.8.3 Pushing changes to another repository
-
-Mercurial lets us push changes to another repository, from the
-repository we’re currently visiting. As with the example of “hg pull”
-above, we’ll create a temporary repository to push our changes into.
-
- $ cd ..
- $ hg clone hello hello-push
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-
-The “hg outgoing” command tells us what changes would be pushed into
-another repository.
-
- $ cd my-hello
- $ hg outgoing ../hello-push
- comparing with ../hello-push
- searching for changes
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
+#### 2.8.2 Using fetch and merge separately to pull
-And the “hg push” command does the actual push.
+Sometimes you may not know if you want to pull in the changes from the
+remote repository or not. It's useful to be able to examine them
+before accepting them into our branch. The "git pull" command shown in
+the previous section is conceptually the combination of two command,
+"git fetch" and "git merge". We can use these commands separately to
+examine the change before accepting it.
- $ hg push ../hello-push
- pushing to ../hello-push
- searching for changes
- adding changesets
- adding manifests
- adding file changes
- added 1 changesets with 1 changes to 1 files
+So let's do that within the hello-fetch clone we made earlier. First
+we will do the fetch:
-As with “hg pull”, the “hg push” command does not update the working
-directory in the repository that it’s pushing changes into. (Unlike
-“hg pull”, “hg push” does not provide a -u option that updates the
-other repository’s working directory.)
+ $ cd ../hello-fetch
+ $ git fetch
+ remote: Generating pack...
+ Unpacking 3 objects...
+ remote: Done counting 5 objects.
+ Result has 3 objects.
+ Deltifying 3 objects...
+ 100% remote: (3/3) done
+ Total 3 (delta 1), reused 0 (delta 0)
+ 100% (3/3) done
+ * refs/remotes/origin/master: fast forward to branch 'master' of /tmp/hello/
+ old..new: a1a0e8b..3c54ac6
+
+You may notice that the output here looks very much like the first
+portion of the output from "git pull". This is no coincidence. The
+new changes have been "fetched" into the current repository and are
+stored into "origin/master" and have not been into the current
+"master" branch. Remember that "master" is our current branch. So now,
+"origin/master" is the state of the master branch that exists in the
+"origin" repository, (the one we cloned from).
+
+The most convenient way to examine the fetched changes is with the
+"master..origin" range notation:
+
+ $ git log master..origin
+ commit 3c54ac672ec1130b36837f1b708054a7a1d402de
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Fri Sep 28 12:50:16 2007 -0700
+
+ Fixed the typo so the program actually compiles now.
+
+Another helpful way of visualizing what happened with "git fetch" here
+is to run "gitk --all", which gives a graphical representation of all
+branches. Here is what it would look like:
+
+[[img gitk-fetch.png]]
+
+Notice that origin/master points to a single commit that was committed
+on top of the state pointed to by the "master" branch.
+
+Let's assume we are happy with the changes and we want to include them
+into our master branch. To do this we simply run "git merge origin":
+
+ $ git merge origin
+ Updating a1a0e8b..3c54ac6
+ Fast forward
+ hello.c | 2 +-
+ 1 files changed, 1 insertions(+), 1 deletions(-)
+
+Again, you'll see that this precisely matches the final portion of the
+output from "git pull". Using "git fetch" and "git merge" let us
+achieve exactly what "git pull" did, but we were able to stop in the
+middle to examine the situation, (and we could have decided to reject
+the changes and not merge them---leaving our master branch unchanged).
+
+##### On merges and "fast forward"
+
+You'll notice that we've been seeing the phrase "fast forward" several
+times. This is a special-case operation performed by "git merge" where
+a branch can be advanced along a linear sequence. This happens
+whenever you pull changes that build directly on top of the same
+commit you have as your most recent commit. In other words, there was
+never any divergence or simultaneous commits created in parallel in
+multiple repositories. If there had been parallel commits, then "git
+merge" would actually introduce a new merge commit to tie the two
+commits together.
+
+When a non-fast-forward merge occurs, there is always the possibility
+that a conflict occurs. In this case, "git merge" will leave conflict
+markers in the files and instruct you to resolve the conflicts. When
+you are finished, you would issue a "git commit -a" to create the
+merge commit.
+
+#### 2.8.3 Using "git remote" to pull changes from other repositories
+
+We've already described how "git pull" will pull in changes from the
+repository which was the origin of the clone operation. Git also
+provides excellent support for pulling changes from any other
+repository as well, (distributed, rather than centralized
+development).
+
+If you have a situation where you want to pull a single time from some
+repository, then you can simply give the path or URL of the repository
+on the "git pull" command line. However, it's often the case that if
+you want to pull changes from a repository once, you'll want to pull
+changes from that same repository again in the future. This is where
+the "git remote" notion is extremely useful---it allows you to
+associate simple names, (and behaviors), with remote repository URLs
+
+We've already seen one instance of "git remote" which is the creation
+of the "origin" remote which happens automatically during "git
+clone". Let's now create another. Let's assume you are going to be
+working in the hello-remote repository and you'd like to pull changes
+from the hello-pull repository, where your friend "fred" has been
+making changes. Here's how to setup the new remote:
+
+ $ cd ../hello-remote
+ $ git remote add fred ../hello-pull
+
+So that's a "git remote add" command line followed by an arbitrary
+name you'd like for the new remote (fred) and the URL of the remote
+(../hello-pull). Obviously, the URL could be a git:// URL or any other
+git-supported URL in addition to a local path.
+
+The "git remote" command is really just a helper for adding some
+entries to the .git/config file. You might find it more convenient to
+edit that file directly once you get comfortable with things.
+
+At this point the name "fred" will work much like the name "origin"
+has worked in previous examples. For example, we can fetch the changes
+fred has made with "git fetch fred":
+
+ $ git fetch fred
+ remote: Generating pack...
+ Unpacking 3 objects...
+ remote: Done counting 5 objects.
+ Result has 3 objects.
+ Deltifying 3 objects...
+ 100% remote: (3/3) done
+ Total 3 (delta 1), reused 0 (delta 0)
+ 100% (3/3) done
+ * refs/remotes/fred/master: storing branch 'master' of ../hello-pull
+ commit: 3c54ac6
+
+Notice that this command-line only differs from the "git fetch" we did
+previously by explicitly naming which remote should be fetched. We
+could have explicitly said "git fetch origin" earlier.
+
+We can also list all known remote-tracking branches with "git branch
+-r":
+
+ $ git branch -r
+ fred/master
+ origin/HEAD
+ origin/master
+
+These remote-tracking branches make it very easy to collaborate with
+people as they are working on experimental features not yet ready for
+upstream inclusion. For example, if fred's latest code is still
+trashing filesystems then he might not want to push it out the the
+project's primary repository. But he may still want my help with
+it. So he can push it to a branch in his own repository for which I've
+got a remote. Then on my next "git fetch fred" I might notice a new
+branch called fred/trashes-filesystems and I can examine his code with
+a command such as "git log ..fred/trashed-filesystems".
+
+So lots of side collaboration can go on easily, and people working
+only with the primary repository never even have to see this dangerous
+code. It's distributed development at its finest.
+
+#### 2.8.4 Checking out previous revisions
+
+It's often useful to examine the working-tree state of some specific
+revision other than the tip of some branch. For example, maybe you
+would like to build a particular tagged version, or maybe you'd like
+to test the behavior of the code before a particular change was
+introduced. To do this, use "git checkout" and pass it the name of any
+revision, (with a branch name, a tag name, or any other commit
+identifier). For example, to examine our project before the original
+typo was introduced:
+
+ $ git checkout 0a633bf5
+ Note: moving to "0a633bf5" which isn't a local branch
+ If you want to create a new branch from this checkout, you may do so
+ (now or later) by using -b with the checkout command again. Example:
+ git checkout -b <new_branch_name>
+ HEAD is now at 0a633bf... Create a makefile
+
+The note that git gives us is to indicate that we are checking out a
+non-branch revision. This is perfectly fine if we are just exploring
+history, but if we actually wanted to use this revision as the basis
+for new commits, we would first have to create a new branch name as it
+describes.
+
+If we were to use "git checkout" with a branch name, then that would
+change the current branch, (meaning that any new commits would advance
+that branch pointer).
+
+For now, let's return back to the tip of the master branch by just
+checking it out again:
+
+ $ git checkout master
+ Previous HEAD position was 0a633bf... Create a makefile
+ Switched to branch "master"
+
+#### 2.8.5 Pushing changes to another repository
+
+As an unsurprising parallel to "git pull", git also provides "git
+push" for pushing changes to another repository. Now, generally the
+purpose of pushing to a repository is to have some "collaboration
+point" where potentially multiple people might be pushing or
+pulling. Because there might be multiple people pushing into the
+repository at any point, it wouldn't make sense to have a
+working-directory associated with this repository.
+
+For this, git has the notion of a "bare" repository, which is simply a
+repository with no working directory. Let's create a new bare
+repository and push some changes into it:
+
+ $ cd ..
+ $ mkdir hello-bare
+ $ cd hello-bare
+ $ git --bare init --shared
+
+The --shared option sets up the necessary group file permissions so
+that other users in my group will be able to push into this repository
+as well.
+
+Now lets return to our hello repository and push some changes to this
+new repository. Since this is our very first push into this repository
+we need to tell git which branches to push. The easiest way to do this
+is to use --all to indicate all branches:
+
+ $ cd ../hello
+ $ git push ../hello-bare --all
+ updating 'refs/heads/master'
+ from 0000000000000000000000000000000000000000
+ to 3c54ac672ec1130b36837f1b708054a7a1d402de
+ Generating pack...
+ Done counting 18 objects.
+ Deltifying 18 objects...
+ 100% (18/18) done
+ Writing 18 objects...
+ 100% (18/18) done
+ Total 18 (delta 3), reused 15 (delta 2)
+ Unpacking 18 objects...
+ 100% (18/18) done
+ refs/heads/master: 0000000000000000000000000000000000000000 -> 3c54ac672ec1130b36837f1b708054a7a1d402de
+
+For subsequent pushes we don't need to specify --all as "git push" by
+default pushes all branches that exist in both the local and remote
+repositories. Also, as with pull, instead of explicitly specifying a
+URL, you may also specify a remote to push to. And by default, after
+cloning a repository, "git push" with no other arguments will attempt
+to push back to the same origin repository. As this is often exactly
+what is wanted, you may find that "git push" alone is often exactly
+what you need.
What happens if we try to pull or push changes and the receiving
repository already has those changes? Nothing too exciting.
- $ hg push ../hello-push
- pushing to ../hello-push
- searching for changes
- no changes found
-
-#### 2.8.4 Sharing changes over a network
-
-The commands we have covered in the previous few sections are not
-limited to working with local repositories. Each works in exactly the
-same fashion over a network connection; simply pass in a URL instead
-of a local path.
-
- $ hg outgoing http://hg.serpentine.com/tutorial/hello
- comparing with http://hg.serpentine.com/tutorial/hello
- searching for changes
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
+ $ git push ../hello-bare
+ Everything up-to-date
-In this example, we can see what changes we could push to the remote
-repository, but the repository is understandably not set up to let
-anonymous users push to it.
-
- $ hg push http://hg.serpentine.com/tutorial/hello
- pushing to http://hg.serpentine.com/tutorial/hello
- searching for changes
- ssl required
-
- [1]: http://hgbook.red-bean.com/hgbookch3.html
- [2]: http://hgbook.red-bean.com/hgbookch1.html
- [3]: http://hgbook.red-bean.com/hgbookch1.html#tailhgbookch1.html
- [4]: #tailhgbookch2.html
- [5]: http://hgbook.red-bean.com/hgbook.html#hgbookch2.html
- [6]: http://mercurial.berkwood.com/
- [7]: http://hgbook.red-bean.com/hgbookli4.html#Xweb:macpython
- [8]: #x6-340581
- [9]: hgbookch2_files/tour-history.png
- [10]: http://hgbook.red-bean.com/hgbookch12.html#x16-27100012.4
- [11]: #x6-420002.7.1
- [12]: #x6-490002.8.1
- [13]: http://hgbook.red-bean.com/hgbookch2.html
-
-## Appendix D
+## Appendix D
Open Publication License
Version 1.0, 8 June 1999
-### D.1 Requirements on both unmodified and modified versions
+### D.1 Requirements on both unmodified and modified versions
The Open Publication works may be reproduced and distributed in whole
or in part, in any medium physical or electronic, provided that the
large as the title of the work and cited as possessive with respect to
the title.
-### D.2 Copyright
+### D.2 Copyright
The copyright to each Open Publication is owned by its author(s) or
designee.
-### D.3 Scope of license
+### D.3 Scope of license
The following license terms apply to all Open Publication works,
unless otherwise explicitly stated in the document.
limited to, the implied warranties of merchantability and fitness for
a particular purpose or a warranty of non-infringement.
-### D.4 Requirements on modified works
+### D.4 Requirements on modified works
All modified versions of documents covered by this license, including
translations, anthologies, compilations and partial documents, must
assert or imply endorsement of the resulting document without the
original author’s (or authors’) permission.
-### D.5 Good-practice recommendations
+### D.5 Good-practice recommendations
In addition to the requirements of this license, it is requested from
and strongly recommended of redistributors that:
CD-ROM expression of an Open Publication-licensed work to its
author(s).
-### D.6 License options
+### D.6 License options
The author(s) and/or publisher of an Open Publication-licensed
document may elect certain options by appending language to the
projects / hgbook-git / blobdiff