-## Chapter 2
-A tour of Mercurial: the basics
+## 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.
* Convert from HTML to markdown source syntax
* Eliminate all content except Chapter 2 and Appendix D
* Eliminate line numbers from examples
+ * Modified to describe git instead of mercurial
-### 2.1 Installing Mercurial on your system
+The source of this modified version can be obtained via git:
-Prebuilt binary packages of Mercurial are available for every popular
-operating system. These make it easy to start using Mercurial on your
+ 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
Because each Linux distribution has its own packaging tools, policies,
and rate of development, it’s difficult to give a comprehensive set of
-instructions on how to install Mercurial binaries. The version of
-Mercurial that you will end up with can vary depending on how active
+instructions on how to install git binaries. The version of
+git that you will end up with can vary depending on how active
the person is who maintains the package for your distribution.
-To keep things simple, I will focus on installing Mercurial from the
+To keep things simple, I will focus on installing git from the
command line under the most popular Linux distributions. Most of these
distributions provide graphical package managers that will let you
-install Mercurial with a single click; the package name to look for is
-mercurial.
+install git with a single click. The package name to look for is
+often git, but is sometimes git-core, (due to an unfortunate name
+with git, meaning GNU Interactive Tools).
- * Debian
+ * Debian
- apt-get install mercurial
+ apt-get install git-core
- * Fedora Core
+ * Fedora Core
- yum install mercurial
+ yum install git
- * Gentoo
+ * Gentoo
- emerge mercurial
+ emerge git
- * OpenSUSE
+ * OpenSUSE
- yum install mercurial
+ yum install git
- * Ubuntu Ubuntu’s Mercurial package is based on Debian’s. To install
-it, run the following command.
+ * Ubuntu
- apt-get install mercurial
+ apt-get install git-core
-The Ubuntu package for Mercurial tends to lag behind the Debian
-version by a considerable time margin (at the time of writing, seven
-months), which in some cases will mean that on Ubuntu, you may run
-into problems that have since been fixed in the Debian package.
+#### 2.1.2 Mac OS X
-#### 2.1.2 Solaris
+A git-core package is available through
+[macports](http://macports.org). Once macports is enabled, the command
+to install git is:
-XXX.
+ port install git-core
-#### 2.1.3 Mac OS X
+#### 2.1.3 Windows
-Lee Cantey publishes an installer of Mercurial for Mac OS X at
-[http://mercurial.berkwood.com][6]. This package works on both
-Intel- and Power-based Macs. Before you can use it, you must install a
-compatible version of Universal MacPython [[BI][7]]. This is easy to
-do; simply follow the instructions on Lee’s site.
-
-#### 2.1.4 Windows
-
-Lee Cantey also publishes an installer of Mercurial for Windows at
-[http://mercurial.berkwood.com][6]. This package has no external
-dependencies; it “just works”.
-
-Note: The Windows version of Mercurial does not automatically convert
-line endings between Windows and Unix styles. If you want to share
-work with Unix users, you must do a little additional configuration
-work. XXX Flesh this out.
+Git has long been available as part of cygwin, and works reasonably
+well in that environment. Some people find cygwin a particularly
+inelegant approach to running git and would prefer a "native"
+solution. To this end, the [msysgit
+project](http://code.google.com/p/msysgit/) is rapidly putting
+together a solution including various packages with full
+installers. These include GitMe, a package to install the entire
+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
+2007).
### 2.2 Getting started
-To begin, we’ll use the “hg version” command to find out whether
-Mercurial is actually installed properly. The actual version
-information that it prints isn’t so important; it’s whether it prints
-anything at all that we care about.
+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
+more friendly to new users than versions 1.4 and older. If you aren't
+yet running version 1.5 or newer, it's highly recommended that you
+upgrade.
- $ hg version
- Mercurial Distributed SCM (version 2937d0dbfab0)
-
- Copyright (C) 2005, 2006 Matt Mackall <mpm@selenic.com>
- This is free software; see the source for copying conditions. There is NO
- warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ $ git version
+ git version 1.5.3.2
#### 2.2.1 Built-in help
-Mercurial 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 “hg help”; it will
-print a brief list of commands, along with a description of what each
-does. If you ask for help on a specific command (as below), it prints
-more detailed information.
-
- $ hg help init
- hg init [-e CMD] [--remotecmd CMD] [DEST]
-
- create a new repository in the given directory
-
- Initialize a new repository in the given directory. If the given
- directory does not exist, it is created.
-
- If no directory is given, the current directory is used.
-
- It is possible to specify an ssh:// URL as the destination.
- Look at the help text for the pull command for important details
- about ssh:// URLs.
-
- options:
-
- -e --ssh specify ssh command to use
- --remotecmd specify hg command to run on the remote side
-
- use "hg -v help init" to show global options
-
-For a more impressive level of detail (which you won’t usually need)
-run “hg help -v”. The -v option is short for --verbose, and tells
-Mercurial to print more information than it usually would.
+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>"?]
+
+ [XXX: The original hgbook includes the complete output of "hg
+ help init" at this point. I'm not including the corresponding
+ "git help init" output as it would be excessively long. The
+ description alone is quite reasonable, (other than a
+ not-too-helpful aside about the obsolete git-init-db command),
+ but it only comes after a full screen's worth of options
+ details. Might it make sense to have a more summarized help
+ output for "git help <foo>" than all of the documentation
+ 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
-In Mercurial, everything happens inside a repository. The repository
+In git, everything happens inside a repository. The repository
for a project contains all of the files that “belong to” that project,
along with a historical record of the project’s files.
There’s nothing particularly magical about a repository; it is simply
-a directory tree in your filesystem that Mercurial treats as
+a directory tree in your filesystem that git treats as
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
-
-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 Mercurial provides. This command
-is called “hg clone”, because it creates an identical copy of an
-existing repository.
-
- $ hg clone http://hg.serpentine.com/tutorial/hello
- destination directory: hello
- requesting all changes
- adding changesets
- adding manifests
- adding file changes
- added 5 changesets with 5 changes to 2 files
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+#### 2.3.1 Creating a local copy of a remote repository
+
+As suggested, a repository can be copied through normal file-copying
+commands. But git also provides a "git clone" tool for copying a
+repository. This provides a means of copying a repository over the
+network, and is also useful with a local repository since it is much
+more efficient than creating a normal copy, (creating a local clones
+is blazingly fast).
+
+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/
+ remote: Generating pack...
+ remote: Done counting 15 objects.
+ remote: Deltifying 15 objects...
+ remote: 100% (15/15) done
+ remote: Total 15 (delta 2), reused 15 (delta remote: 2)
+ Indexing 15 objects...
+ 100% (15/15) done
+ Resolving 2 deltas...
+ 100% (2/2) done
+
+If for some reason you are prevented from talking on the git: port,
+then there is also the capability to clone a repository (less
+efficiently) over http:
+
+ $ git clone http://cworth.org/git/hello
+ Initialized empty Git repository in /tmp/hello/.git/
+ Getting alternates list for http://cworth.org/git/hello
+ Getting pack list for http://cworth.org/git/hello
+ Getting index for pack 04ecb061314ecbd60fa0610ecf55a1cbf85ea294
+ Getting pack 04ecb061314ecbd60fa0610ecf55a1cbf85ea294
+ which contains a1a0e8b392b17caf50325498df54802fe3c03710
+ walk a1a0e8b392b17caf50325498df54802fe3c03710
+ walk 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ walk 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ walk 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
+ walk db7117a9dd9a6e57e8632ea5848e1101eee0fbde
If our clone succeeded, we should now have a local directory called
hello. This directory will contain some files.
- $ ls -l
- total 4
- drwxrwxr-x 3 bos bos 4096 Jun 17 18:05 hello
- $ ls hello
- Makefile hello.c
+ $ ls -l
+ total 4
+ drwxr-xr-x 3 cworth cworth 4096 2007-09-27 16:40 hello
+ $ ls hello
+ hello.c Makefile
These files have the same contents and history in our repository as
they do in the repository we cloned.
-Every Mercurial repository is complete, self-contained, and
+Every git repository is complete, self-contained, and
independent. It contains its own private copy of a project’s files and
history. A cloned repository remembers the location of the repository
it was cloned from, but it does not communicate with that repository,
#### 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 .hg. This is where Mercurial keeps all
+it contains a directory named .git. This is where git keeps all
of its metadata for the repository.
- $ cd hello
- $ ls -a
- . .. .hg Makefile hello.c
+ $ cd hello
+ $ ls -a
+ . .. .git hello.c Makefile
-The contents of the .hg directory and its subdirectories are private
-to Mercurial. Every other file and directory in the repository is
+The contents of the .git directory and its subdirectories are private
+to git. Every other file and directory in the repository is
yours to do with as you please.
-To introduce a little terminology, the .hg directory is the “real”
+To introduce a little terminology, the .git directory is the “real”
repository, and all of the files and directories that coexist with it
are said to live in the working directory. An easy way to remember the
distinction is that the repository contains the history of your
### 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
By default, this command prints a brief paragraph of output for each
-change to the project that was recorded. In Mercurial terminology, we
-call each of these recorded events a changeset, because it can contain
-a record of changes to several files.
-
-The fields in a record of output from “hg log” are as follows.
-
- * 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.
-
-The default output printed by “hg log” is purely a summary; it is
+change to the project that was recorded. In git terminology, we
+call each of these recorded events a commit.
+
+The 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
+ 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). The "git log" command doesn't display
+ the Committer, but other git tools do.
+ * 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 default output printed by “git log” is purely a summary; it is
missing a lot of detail.
-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.
-
-* * *
-
-![PIC][9]
-
-Figure 2.1:
-Graphical history of the hello repository
-
-* * *
-
-#### 2.4.1 Changesets, revisions, and talking to other people
+#### 2.4.1 Commits, revisions, and talking to other people
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.
+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.
- $ 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.
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 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
+ 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.
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
+ Introduce a typo into hello.c.
+
+#### 2.4.4 Other log filters
-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”.
+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 "--" wihch is necessary to distinguish
+commit names from file names:
- $ 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.
+ $ git log -- Makefile
+ 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.
+ commit 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
+ Author: Bryan O'Sullivan <mpm@selenic.com>
+ Date: Fri Aug 26 01:21:28 2005 -0700
+ Create a makefile
+
+And "git log" can also filter based on the dates at which commits were
+created:
+
+ $ git log --since="2 weeks ago" --until="yesterday"
-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.
+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
+
+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:
+
+ $ git log --stat --max-count=3
+ commit a1a0e8b392b17caf50325498df54802fe3c03710
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 15:43:07 2005 -0700
+ Trim comments.
-
-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 | 8 ++------
+ 1 files changed, 2 insertions(+), 6 deletions(-)
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 2005 -0700
- 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 @@
+ Get make to generate the final binary from a .o file.
- int main(int argc, char ⋆⋆argv)
- {
- - printf("hello, world!∖n");
- + printf("hello, world!∖");
- return 0;
- }
+ Makefile | 2 ++
+ 1 files changed, 2 insertions(+), 0 deletions(-)
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
+
+ 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 --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
+
+ Introduce a typo into hello.c.
+
+ 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 Mercurial commands to discuss
+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).
- * 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.
+ * 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).
-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.
+ * Option naming and usage is consistent across commands. For
+ 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.
-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).
+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 Mercurial, let’s take a
+Now that we have a grasp of viewing history in git, 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
+its own. We use the “git 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
+ $ cd ..
+ $ git clone hello my-hello
+ Initialized empty Git repository in /tmp/my-hello/.git/
+ 0 blocks
+
+ [XXX We say "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?]
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
local clones are so cheap, there’s almost no overhead to cloning and
destroying repositories whenever you want.
+Alternatively, you can achieve much the same effect by creating
+multiple branches in a single repository, (but we won't go into detail
+on how to do that in this chapter). Some people greatly appreciate
+having multiple branches in a single repository rather than having
+many repositories cluttering up their filesystem. Other people prefer
+the ability to have working-tree changes, and intermediate build
+files, etc. each isolated in a separate repository per branch. Both
+modes are very well-supported by git, so it's really a matter of which
+you find most appropriate at any time given your tastes and project
+workflows.
+
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
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
+ $ 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.
+The “git status” command will tell us what git knows about the files
+in the repository.
- $ ls
- Makefile hello.c
- $ hg status
- M hello.c
+ $ 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")
-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.
+We see that “git status” command prints a line with "modified" for
+hello.c. The “git status” command 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.
+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..6d28887 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -8,5 +8,6 @@
+ int main(int argc, char **argv)
+ {
+ printf("hello, world!\");
+ + printf("hello again!\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.
+record our work in a new commit.
-The “hg commit” command lets us create a new changeset; we’ll usually
+The “git 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.
+When you try to run “git commit” for the first time, it might not do
+exactly what you want. Git records your name and 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. It will
+attempt each of the following methods, in order, (stopping for each field 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 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.
+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 a valid
+email address, but some, (notably Linus Torvalds, the original author
+of git), actually like the default user@hostname convention that git
+falls back on without any additional information. 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.
#### 2.7.2 Writing a commit message
-When we commit a change, Mercurial drops us into a text editor, to
+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:”.
-
- empty line
- HG: changed hello.c
-
-Mercurial ignores the lines that start with “HG:”; it uses them only
+ $ 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 “#”.
+
+ 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
+ #
+
+git ignores the lines that start with “#”; it uses them only
to tell us which files it’s recording changes to. Modifying or
deleting these lines has no effect.
#### 2.7.3 Writing a good commit message
-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
+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.
+
+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.
+
+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 -p".
#### 2.7.4 Aborting a commit
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
+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 018cfb742be6176443ffddac454e593e802ddf3e
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Thu Sep 27 23:55:00 2007 -0700
+ Added an extra line of output.
+
+ If I would have been clever I would have fixed that old typo
+ while I was at it...
- 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;
- }
+ diff --git a/hello.c b/hello.c
+ index 9a3ff79..6d28887 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -8,5 +8,6 @@
+ int main(int argc, char **argv)
+ {
+ printf("hello, world!\");
+ + printf("hello again!\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 commit with a
+careful message, we're just about ready to share our change with the
+world. But wait, we forgot to try to compile it didn't we?
+
+ $ make
+ cc -c -o hello.o hello.c
+ hello.c:10:9: warning: missing terminating " character
+ hello.c:10:9: warning: missing terminating " character
+ hello.c: In function ‘main’:
+ hello.c:10: error: missing terminating " character
+ hello.c:11: error: expected ‘)’ before ‘;’ token
+ hello.c:13: warning: passing argument 1 of ‘printf’ makes pointer from integer without a cast
+ hello.c:13: error: expected ‘;’ before ‘}’ token
+ make: *** [hello.o] Error 1
+
+Oh look. The code's broken and doesn't compile. We don't want to share
+code in this state. For situations where you notice one tiny detail
+that got left out of the last commit, (a silly syntax error, a
+misspelling in a comment or commit messsage), git provides a very
+handy tool for just changing the last commit.
+
+So fix that typo, (a missing 'n' between the '\' and the '"'), with
+your editor or with something like this:
+
+ sed -i 's/\\"/\\n"/' hello.c
+
+And then you can just amend the previous commit rather than creating a
+new one with the --amend option to "git commit":
+
+ $ git commit -a --amend
+
+Note that we use -a to include the code change here. And that helps
+point out a situation where "git commit" is useful without the -a
+option, "git commit --amend" is a useful command for amend just the
+last commit message, without committing any new code changes, even if
+some files have been modified in the working tree.
+
+And here's the final result:
+
+ $ git show
+ commit 839b58d021c618bd0e1d336d4d5878a0082672e6
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Thu Sep 27 23:55:00 2007 -0700
-
-We refer to the newest revision in the repository as the tip revision,
-or simply the tip.
+ Added an extra line of output and fixed the typo bug.
+
+ diff --git a/hello.c b/hello.c
+ index 9a3ff79..ca750e0 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -7,6 +7,7 @@
+
+ int main(int argc, char **argv)
+ {
+ - printf("hello, world!\");
+ + printf("hello, world!\n");
+ + printf("hello again!\n");
+ return 0;
+ }
+
+I can't help but point out that this really was a poor example for
+--amend. The end result is a single commit that does two independent
+things, (fixes one bug and adds one new feature). It's much better to
+create a code history where each commit makes an independent change,
+(and as small as possible). This is important for several reasons:
+
+ * Small changes are easier to review
+
+ * Independent changes are easier to split up if only part of the
+ series gets accepted "upstream" for one reason or another.
+
+ * 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 the single commit that introduces a bug. And
+ it's much more powerful if the commit it isolates is as small as
+ possible.
+
+So it's a good thing this document is available under a license that
+allows for distribution of modified versions. Someone should clean up
+the --amend example to not teach bad habits like I did above. [Note:
+All this bad-habit stuff was introduced by me, and was not present in
+Bryan's original chapter. -Carl]
### 2.8 Sharing changes
-We mentioned earlier that repositories in Mercurial are
-self-contained. This means that the changeset we just created exists
+We mentioned earlier that repositories in git are
+self-contained. This means that the commit 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.
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
-
-
-(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.)
-
-Bringing changes into a repository is a simple matter of running the
-“hg pull” command, and telling it which repository to pull from.
-
- $ 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
-
-
-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.
+ $ cd ..
+ $ git clone hello hello-pull
+ Initialized empty Git repository in /tmp/hello-pull/.git/
+ 0 blocks
+
+We could use the “git pull” command to apply changes from my-hello to
+our master branch in hello-pull. However, blindly pulling unknown
+changes into a repository is a somewhat scary prospect. The "git pull"
+command is coneptually the combination of two commands, "git fetch"
+and "git merge"; we can run those separately to examine the changes
+before applying them locally. First we do the fetch:
+
+ $ cd hello-pull
+ $ git fetch ../my-hello
+ 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)
+
+The fetched commits (or commit in this case) are available as the name
+FETCH_HEAD. [XXX: Shouldn't git-fetch print that name out to the user
+if the user didn't provide a specific branch name to fetch into.] And
+the difference between what we had before and what exists on
+FETCH_HEAD can easily be examined with the ..FETCH_HEAD range
+notation:
+
+ $ git log ..FETCH_HEAD
+ commit 839b58d021c618bd0e1d336d4d5878a0082672e6
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Thu Sep 27 23:55:00 2007 -0700
- $ 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.
+ Added an extra line of output and fixed the typo bug.
+
+Since these commits actually exist in the local repository now, we
+don't need to fetch or pull them from the remote repository again---we
+can now use "git merge" to apply the previously fetched commits. (A
+mercurial user might notice here that git does not have the race
+condition between "hg incoming" and "hg pull" that mercurial has since
+the commits are fetched only once.)
+
+ $ git merge FETCH_HEAD
+ Updating a1a0e8b..839b58d
+ Fast forward
+ hello.c | 3 ++-
+ 1 files changed, 2 insertions(+), 1 deletions(-)
+
+Notice that "git merge" reports that our branch pointer has been
+updated from a1a0e8b to 839b58d. Also, this is a "fast forward"
+meaning that the new commits are a linear sequence on top of the
+commit we already hand. In other words, there wasn't any divergence
+between these two repositories so no actual "merge" commit was
+created.
+
+This separation of fetch and merge is useful when you need to
+carefully review some changes before applying them. But often you're
+in a situation where you know you trust the remote repository and you
+simply want to pull those changes as conveniently as possible, (no
+extra commands, no typing a magic name like FETCH_HEAD). This is the
+case when the tracking upstream development of a project with git. And
+in that case, the above steps are as simple as just executing "git
+pull". So let's repeat all that the simpler way:
+
+ $ cd ..
+ $ git clone hello hello-tracking
+ Initialized empty Git repository in /tmp/hello-tracking/.git/
+ 0 blocks
+ $ cd hello-tracking
+ $ git pull ../my-hello
+ remote: Generating pack...
+ remote: Done counting 5 objects.
+ Result has 3 objects.
+ Deltifying 3 objects...
+ Unpacking 3 objects...
+ remote: 100% (3/3) done
+ Total 3 (delta 1), reused 0 (delta 0)
+ 100% (3/3) done
+ Updating a1a0e8b..839b58d
+ Fast forward
+ hello.c | 3 ++-
+ 1 files changed, 2 insertions(+), 1 deletions(-)
+
+It should be plain to see that the "git pull" command really did the
+combined sequence of "git fetch" and "git merge". Also, if you want to
+pull from the same repository you cloned from originally, (which is
+the common case for the upstream-tracking scenario), then "git pull"
+with no explicit repository is suffcient, and it will default to
+pulling from the same repository as the original clone.
+
+[XXX: The structure of the preceding section follows that of the
+original hgbook. But an alternate structure that arranged to pull from
+the originally cloned repository (as would be common) would allow for
+more straightforward use of git's features. For example, instead of
+the silly FETCH_HEAD stuff it would allow for "git fetch" and "git log
+master..origin" to be a very nice replacement for "hg
+incoming". Similarly, below, "git log origin..master" would make a
+nice replacement for "hg outgoing" which is something I didn't offer
+at all. One could also use git's remotes with the myriad repositories
+as used here, but it would require doing things like "git remote add
+<some-name> ../hello-pull" and that seems like a bit much to introduce
+for a turorial of this level. If nothing else, if the above section
+seems a little intimidating, understand that it's because things are
+not presented in the most natural "git way", (and I'm a little too
+tired to fix it tonight).]
+
+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 workind-directory files as necessary.
+
+#### 2.8.2 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"
#### 2.8.3 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
-
-
-And the “hg push” command does the actual push.
-
- $ 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
-
-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.)
+Git lets us push changes to another repository, from the repository
+we’re currently visiting. As with previous examples, above, we’ll
+first create a temporary repository to push our changes into. But
+instead of using "git clone", this time we'll use "git init" to make a
+repository from an empty directory. We do this to create a "bare"
+repository which is simply a repository that has no working-directory
+files associated with it. In general, you should only push to bare
+repositories.
+
+ $ cd ..
+ $ mkdir hello-push
+ $ cd hello-push
+ $ git --bare init
+ Initialized empty Git repository in /tmp/hello-push/
+
+And then we'll go back to our my-hello repository to perform the
+push. 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 ../my-hello
+ $ git push ../hello-push --all
+ updating 'refs/heads/master'
+ from 0000000000000000000000000000000000000000
+ to 839b58d021c618bd0e1d336d4d5878a0082672e6
+ 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 0 (delta 0)
+ Unpacking 18 objects...
+ 100% (18/18) done
+ refs/heads/master: 0000000000000000000000000000000000000000 -> 839b58d021c618bd0e1d336d4d5878a0082672e6
+
+For subsequent pushes we don't need to specify --all as "git push"
+will push all branches that exist in both the local and remote
+repositories.
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
+ $ git push ../hello-push
+ Everything up-to-date
#### 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
-
+same fashion over a network connection; simply pass in a URL or an ssh
+host:/path/name specification instead of a local path.
-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
[http://www.opencontent.org/openpub/][http://www.opencontent.org/openpub/]).
The reference must be immediately followed with any options elected by
-the author(s) and/or publisher of the document (see section D.6).
+the author(s) and/or publisher of the document (see section D.6).
Commercial redistribution of Open Publication-licensed material is
permitted.
projects / hgbook-git / blobdiff