2 A tour of git: the basics
6 This document is a modified version originally known as "Distributed
7 revision control with Mercurial" and originally authored by Bryan
8 O’Sullivan. The original document was obtained from
9 <http://hgbook.red-bean.com/>.
11 Copyright © 2006, 2007 Bryan O’Sullivan.
13 This material may be distributed only subject to the terms and
14 conditions set forth in version 1.0 of the Open Publication
15 License. Please refer to Appendix D for the license text.
17 As this is a modified version, the name of Bryan O'Sullivan is used
18 only to properly credit him with the original text. The appearance of
19 his name here explicitly does not assert or imply his endorsement of
20 this modified document.
22 Portions Copyright © 2007 Carl Worth.
24 Changes made by Carl include the following:
27 * Convert from HTML to markdown source syntax
28 * Eliminate all content except Chapter 2 and Appendix D
29 * Eliminate line numbers from examples
30 * Modified to describe git instead of mercurial
32 ### 2.1 Installing git on your system
34 Prebuilt binary packages of git are available for many popular
35 operating systems. These make it easy to start using git on your
40 Because each Linux distribution has its own packaging tools, policies,
41 and rate of development, it’s difficult to give a comprehensive set of
42 instructions on how to install git binaries. The version of
43 git that you will end up with can vary depending on how active
44 the person is who maintains the package for your distribution.
46 To keep things simple, I will focus on installing git from the
47 command line under the most popular Linux distributions. Most of these
48 distributions provide graphical package managers that will let you
49 install git with a single click. The package name to look for is
50 often git, but is sometimes git-core, (due to an unfortunate name
51 with git, meaning GNU Interactive Tools).
55 apt-get install git-core
75 A git-core package is available through
76 [macports](http://macports.org). Once macports is enabled, the command
83 Git has long been available as part of cygwin, and works reasonably
84 well in that environment. Some people find cygwin a particularly
85 inelegant approach to running git and would prefer a "native"
86 solution. To this end, the [msysgit
87 project](http://code.google.com/p/msysgit/) is rapidly putting
88 together a solution including various packages with full
89 installers. These include GitMe, a package to install the entire
90 development environment necessary to work on improving the msysgit
91 port of git, and WinGit, a package for installing just git itself
92 without the development environment, (still in Alpha as of September
95 ### 2.2 Getting started
97 To begin, we’ll use the “git version” command to find out whether git
98 is actually installed properly. Versions 1.5 and newer of git are much
99 more friendly to new users than versions 1.4 and older. If you aren't
100 yet running version 1.5 or newer, it's highly recommended that you
106 #### 2.2.1 Built-in help
108 Git provides a built-in help system. This is invaluable for those
109 times when you find yourself stuck trying to remember how to run a
110 command. If you are completely stuck, simply run “git help”; it will
111 print a brief list of commonly-used commands, along with a description
112 of what each does. If you ask for help on a specific command (such as
113 "git help init"), it prints more detailed information. [XXX: Does "git
114 help <foo>" work universally as a built-in or does it expect man to be
115 present and just call out to "man git-<foo>"?]
117 [XXX: The original hgbook includes the complete output of "hg
118 help init" at this point. I'm not including the corresponding
119 "git help init" output as it would be excessively long. The
120 description alone is quite reasonable, (other than a
121 not-too-helpful aside about the obsolete git-init-db command),
122 but it only comes after a full screen's worth of options
123 details. Might it make sense to have a more summarized help
124 output for "git help <foo>" than all of the documentation
125 available for git-<foo>? And perhaps alos provide a "git -v
126 help" similar to "hg -v help" for more?]
128 ### 2.3 Working with a repository
130 In git, everything happens inside a repository. The repository
131 for a project contains all of the files that “belong to” that project,
132 along with a historical record of the project’s files.
134 There’s nothing particularly magical about a repository; it is simply
135 a directory tree in your filesystem that git treats as
136 special. You can rename or delete a repository any time you like,
137 using either the command line or your file browser.
139 #### 2.3.1 Making a local copy of a repository
141 Copying a repository is just a little bit special. While you could use
142 a normal file copying command to make a copy of a repository, it’s
143 best to use a built-in command that git provides. This command
144 is called “git clone”, because it creates an identical copy of an
147 $ git clone git://cworth.org/git/hello
148 Initialized empty Git repository in /tmp/hello/.git/
149 remote: Generating pack...
150 remote: Done counting 15 objects.
151 remote: Deltifying 15 objects...
152 remote: 100% (15/15) done
153 remote: Total 15 (delta 2), reused 15 (delta remote: 2)
154 Indexing 15 objects...
156 Resolving 2 deltas...
159 If for some reason you are prevented from talking on the git: port,
160 then there is also the capability to clone a repository (less
161 efficiently) over http:
163 $ git clone http://cworth.org/git/hello
164 Initialized empty Git repository in /tmp/hello/.git/
165 Getting alternates list for http://cworth.org/git/hello
166 Getting pack list for http://cworth.org/git/hello
167 Getting index for pack 04ecb061314ecbd60fa0610ecf55a1cbf85ea294
168 Getting pack 04ecb061314ecbd60fa0610ecf55a1cbf85ea294
169 which contains a1a0e8b392b17caf50325498df54802fe3c03710
170 walk a1a0e8b392b17caf50325498df54802fe3c03710
171 walk 72d4f10e4a27dbb09ace1503c20dbac1912ee451
172 walk 13ed136b983a9c439eddeea8a1c2076cffbb685f
173 walk 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
174 walk db7117a9dd9a6e57e8632ea5848e1101eee0fbde
176 If our clone succeeded, we should now have a local directory called
177 hello. This directory will contain some files.
181 drwxr-xr-x 3 cworth cworth 4096 2007-09-27 16:40 hello
185 These files have the same contents and history in our repository as
186 they do in the repository we cloned.
188 Every git repository is complete, self-contained, and
189 independent. It contains its own private copy of a project’s files and
190 history. A cloned repository remembers the location of the repository
191 it was cloned from, but it does not communicate with that repository,
192 or any other, unless you tell it to.
194 What this means for now is that we’re free to experiment with our
195 repository, safe in the knowledge that it’s a private “sandbox” that
196 won’t affect anyone else.
198 #### 2.3.2 What’s in a repository?
200 When we take a more detailed look inside a repository, we can see that
201 it contains a directory named .git. This is where git keeps all
202 of its metadata for the repository.
206 . .. .git hello.c Makefile
208 The contents of the .git directory and its subdirectories are private
209 to git. Every other file and directory in the repository is
210 yours to do with as you please.
212 To introduce a little terminology, the .git directory is the “real”
213 repository, and all of the files and directories that coexist with it
214 are said to live in the working directory. An easy way to remember the
215 distinction is that the repository contains the history of your
216 project, while the working directory contains a snapshot of your
217 project at a particular point in history.
219 ### 2.4 A tour through history
221 One of the first things we might want to do with a new, unfamiliar
222 repository is understand its history. The “git log” command gives us a
226 commit a1a0e8b392b17caf50325498df54802fe3c03710
227 Author: Bryan O'Sullivan <bos@serpentine.com>
228 Date: Tue Sep 6 15:43:07 2005 -0700
232 commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
233 Author: Bryan O'Sullivan <bos@serpentine.com>
234 Date: Tue Sep 6 13:15:58 2005 -0700
236 Get make to generate the final binary from a .o file.
238 commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
239 Author: Bryan O'Sullivan <bos@serpentine.com>
240 Date: Tue Sep 6 13:15:43 2005 -0700
242 Introduce a typo into hello.c.
244 commit 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
245 Author: Bryan O'Sullivan <mpm@selenic.com>
246 Date: Fri Aug 26 01:21:28 2005 -0700
250 commit db7117a9dd9a6e57e8632ea5848e1101eee0fbde
251 Author: Bryan O'Sullivan <mpm@selenic.com>
252 Date: Fri Aug 26 01:20:50 2005 -0700
254 Create a standard "hello, world" program
256 By default, this command prints a brief paragraph of output for each
257 change to the project that was recorded. In git terminology, we
258 call each of these recorded events a commit.
260 The fields in a record of output from “git log” are as follows.
262 * commit This field consists of a string of 40 hexadecimal characters.
263 This is a unique identifier for referring to particular commits.
264 * Author The identity of the person who authored the commit. This
265 field consist of two sub-fields for the user's name and email
266 address, (or at least an email-like idenitifer). Note that git
267 stores a separate "Committer" field for the person who commited
268 the change, (since often an author will email a change to a
269 maintainer that commits it). The "git log" command doesn't display
270 the Committer, but other git tools do.
271 * Date The date and time on which the commit was authored, (again
272 stored separately from the date the change was committed).
273 timezone in which it was created. (The date and time are displayed
274 in the timezone of the person who created the commit.)
275 * commit message The text message that the creator of the commit
276 entered to describe the commit, (generally a one-line summary
277 followed by more supporting text).
279 The default output printed by “git log” is purely a summary; it is
280 missing a lot of detail.
282 Figure [2.1][8] provides a graphical representation of the history of
283 the hello repository, to make it a little easier to see which
284 direction history is “flowing” in. We’ll be returning to this figure
285 several times in this chapter and the chapter that follows.
292 Graphical history of the hello repository
296 #### 2.4.1 Commits, revisions, and talking to other people
298 As English is a notoriously sloppy language, and computer science has
299 a hallowed history of terminological confusion (why use one term when
300 four will do?), revision control has a variety of words and phrases
301 that mean the same thing. If you are talking about git history
302 with other people, you will find that what we have called a “commit”
303 is often called a "revision". In other systems, a similar notion
304 is referred to as a "changeset". You might even see abbreviations of
305 these terms such as "rev", "change", or even "cset".
307 While it may not matter much what word you use to refer to the concept
308 of “a commit”, it's important to know how to name “a specific
309 commit”. We have already seen one means of referring to a particular
310 commit, the 40-character hexadecimal string shown by "git log". These
311 commit identifiers are powerful because they are permanent, unique
312 identifiers that always identify the same commit in any copy of a
313 repository. If two users are examining a working directory associated
314 with the same commit identifier, then those two users have precisely
315 the same contents in all files, and exactly the same history leading
318 So there are places where it is often important to archive the
319 complete commit identifier, (perhaps in bug-tracking systems to
320 indicate a specific commit that fixes a bug, for example). But often,
321 in more casual settings, it's more convenient to use abbreviated
322 commit identifiers. Git accept any unique prefix of a commit
323 identifier, (and for reasonably-sized project the first 8 or 10
324 characters are almost always unique).
326 And unlike the permanent commit identifiers, git also provides
327 transient means of identifying commits. In fact, in day-to-day use of
328 git, you will probably use these names more than commit
329 identifiers. One example is branch names, (such as the default
330 "master" branch in any git repository), or any project-specific branch
331 names such as "stable", "experimental", or "crazy-insane-changes". Git
332 also provides a special name "HEAD" which always refers to the current
335 #### 2.4.2 Naming related commits
337 Git offers simple ways to name revisions that are related to
338 particular revisions in the history. One syntax is the ~ suffix which
339 refers to the parent of a commit, or if followed by a number, to the
340 Nth parent. For example, since "HEAD" refers to the most recent commit
341 in the current branch, "HEAD~", refers to the previous commit, and
342 "HEAD~2" refers to two commits back in the history.
344 Another useful syntax is .. which can be used to specify a range of
345 commits. So "origin..master" specifies everything that has been
346 committed to master since it derived from origin.
348 #### 2.4.3 Viewing specific revisions
350 You can use "git log" to explore the range syntax just introduced. For
351 example, to see a list of the most recent 3 revisions you can use
352 "HEAD~3..", (the destination of the range is implicitly HEAD in this
356 commit a1a0e8b392b17caf50325498df54802fe3c03710
357 Author: Bryan O'Sullivan <bos@serpentine.com>
358 Date: Tue Sep 6 15:43:07 2005 -0700
362 commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
363 Author: Bryan O'Sullivan <bos@serpentine.com>
364 Date: Tue Sep 6 13:15:58 2005 -0700
366 Get make to generate the final binary from a .o file.
368 commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
369 Author: Bryan O'Sullivan <bos@serpentine.com>
370 Date: Tue Sep 6 13:15:43 2005 -0700
372 Introduce a typo into hello.c.
374 #### 2.4.4 Other log filters
376 Besides filtering by commit identifiers, git allows you to easily
377 filter the log output according to which files (or directories) are
378 modified by listing them after "--" wihch is necessary to distinguish
379 commit names from file names:
381 $ git log -- Makefile
382 commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
383 Author: Bryan O'Sullivan <bos@serpentine.com>
384 Date: Tue Sep 6 13:15:58 2005 -0700
386 Get make to generate the final binary from a .o file.
388 commit 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
389 Author: Bryan O'Sullivan <mpm@selenic.com>
390 Date: Fri Aug 26 01:21:28 2005 -0700
394 And "git log" can also filter based on the dates at which commits were
397 $ git log --since="2 weeks ago" --until="yesterday"
399 Another useful option is -n or --max-count which, unsurprisingly,
400 limits the maximum number of commits to be displayed.
402 #### 2.4.3 More detailed information
404 While the default information printed by “git log” is useful if you
405 already know what you’re looking for, you may need to see more details
406 of the change, such as the "diffstat" information with --stat:
408 $ git log --stat --max-count=3
409 commit a1a0e8b392b17caf50325498df54802fe3c03710
410 Author: Bryan O'Sullivan <bos@serpentine.com>
411 Date: Tue Sep 6 15:43:07 2005 -0700
416 1 files changed, 2 insertions(+), 6 deletions(-)
418 commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
419 Author: Bryan O'Sullivan <bos@serpentine.com>
420 Date: Tue Sep 6 13:15:58 2005 -0700
422 Get make to generate the final binary from a .o file.
425 1 files changed, 2 insertions(+), 0 deletions(-)
427 commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
428 Author: Bryan O'Sullivan <bos@serpentine.com>
429 Date: Tue Sep 6 13:15:43 2005 -0700
431 Introduce a typo into hello.c.
434 1 files changed, 1 insertions(+), 1 deletions(-)
436 Or perhaps you'd like to see the actual patch content of each change,
437 which you can get with -p. That commit with the word typo in its name
438 looks suspicous, so let's tak a closer look. Remember that we can name
439 it as master~3, HEAD~3, or any prefix of its commit identifier, (such
442 $ git log -p -n 1 13ed136b
443 commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
444 Author: Bryan O'Sullivan <bos@serpentine.com>
445 Date: Tue Sep 6 13:15:43 2005 -0700
447 Introduce a typo into hello.c.
449 diff --git a/hello.c b/hello.c
450 index ed55ec0..80b260c 100644
455 int main(int argc, char **argv)
457 - printf("hello, world!\n");
458 + printf("hello, world!\");
462 Of course, wanting to see all this information for a single commit is
463 such a common operation that it's given its own name in git, "git
464 show". So "git show 13ed136b" is a much easier way to get exactly the
468 commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
469 Author: Bryan O'Sullivan <bos@serpentine.com>
470 Date: Tue Sep 6 13:15:43 2005 -0700
472 Introduce a typo into hello.c.
474 diff --git a/hello.c b/hello.c
475 index ed55ec0..80b260c 100644
480 int main(int argc, char **argv)
482 - printf("hello, world!\n");
483 + printf("hello, world!\");
487 ### 2.5 All about command options
489 Let’s take a brief break from exploring Mercurial commands to discuss
490 a pattern in the way that they work; you may find this useful to keep
491 in mind as we continue our tour.
493 Mercurial has a consistent and straightforward approach to dealing
494 with the options that you can pass to commands. It follows the
495 conventions for options that are common to modern Linux and Unix
498 * Every option has a long name. For example, as we’ve already seen,
499 the “hg log” command accepts a --rev option.
500 * Most options have short names, too. Instead of --rev, we can use
501 -r. (The reason that some options don’t have short names is that
502 the options in question are rarely used.)
503 * Long options start with two dashes (e.g. --rev), while short
504 options start with one (e.g. -r).
505 * Option naming and usage is consistent across commands. For
506 example, every command that lets you specify a changeset ID or
507 revision number accepts both -r and --rev arguments.
509 In the examples throughout this book, I use short options instead of
510 long. This just reflects my own preference, so don’t read anything
513 Most commands that print output of some kind will print more output
514 when passed a -v (or --verbose) option, and less when passed -q (or
517 ### 2.6 Making and reviewing changes
519 Now that we have a grasp of viewing history in Mercurial, let’s take a
520 look at making some changes and examining them.
522 The first thing we’ll do is isolate our experiment in a repository of
523 its own. We use the “hg clone” command, but we don’t need to clone a
524 copy of the remote repository. Since we already have a copy of it
525 locally, we can just clone that instead. This is much faster than
526 cloning over the network, and cloning a local repository uses less
527 disk space in most cases, too.
530 $ hg clone hello my-hello
531 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
534 As an aside, it’s often good practice to keep a “pristine” copy of a
535 remote repository around, which you can then make temporary clones of
536 to create sandboxes for each task you want to work on. This lets you
537 work on multiple tasks in parallel, each isolated from the others
538 until it’s complete and you’re ready to integrate it back. Because
539 local clones are so cheap, there’s almost no overhead to cloning and
540 destroying repositories whenever you want.
542 In our my-hello repository, we have a file hello.c that contains the
543 classic “hello, world” program. Let’s use the ancient and venerable
544 sed command to edit this file so that it prints a second line of
545 output. (I’m only using sed to do this because it’s easy to write a
546 scripted example this way. Since you’re not under the same constraint,
547 you probably won’t want to use sed; simply use your preferred text
548 editor to do the same thing.)
550 $ sed -i '/printf/a∖∖tprintf("hello again!∖∖n");' hello.c
552 Mercurial’s “hg status” command will tell us what Mercurial knows
553 about the files in the repository.
560 The “hg status” command prints no output for some files, but a line
561 starting with “M” for hello.c. Unless you tell it to, “hg status” will
562 not print any output for files that have not been modified.
564 The “M” indicates that Mercurial has noticed that we modified
565 hello.c. We didn’t need to inform Mercurial that we were going to
566 modify the file before we started, or that we had modified the file
567 after we were done; it was able to figure this out itself.
569 It’s a little bit helpful to know that we’ve modified hello.c, but we
570 might prefer to know exactly what changes we’ve made to it. To do
571 this, we use the “hg diff” command.
574 diff -r b57f9a090b62 hello.c
575 --- a/hello.c Tue Sep 06 15:43:07 2005 -0700
576 +++ b/hello.c Sun Jun 17 18:05:50 2007 +0000
577 @@ -8,5 +8,6 @@ int main(int argc, char ⋆⋆argv)
578 int main(int argc, char ⋆⋆argv)
580 printf("hello, world!∖");
581 + printf("hello again!∖n");
585 ### 2.7 Recording changes in a new changeset
587 We can modify files, build and test our changes, and use “hg status”
588 and “hg diff” to review our changes, until we’re satisfied with what
589 we’ve done and arrive at a natural stopping point where we want to
590 record our work in a new changeset.
592 The “hg commit” command lets us create a new changeset; we’ll usually
593 refer to this as “making a commit” or “committing”.
595 #### 2.7.1 Setting up a username
597 When you try to run “hg commit” for the first time, it is not
598 guaranteed to succeed. Mercurial records your name and address with
599 each change that you commit, so that you and others will later be able
600 to tell who made each change. Mercurial tries to automatically figure
601 out a sensible username to commit the change with. It will attempt
602 each of the following methods, in order:
604 1. If you specify a -u option to the “hg commit” command on the
605 command line, followed by a username, this is always given the
607 2. If you have set the HGUSER environment variable, this is checked next.
608 3. If you create a file in your home directory called .hgrc, with a
609 username entry, that will be used next. To see what the contents
610 of this file should look like, refer to section [2.7.1][11]
612 4. If you have set the EMAIL environment variable, this will be used
614 5. Mercurial will query your system to find out your local user name
615 and host name, and construct a username from these
616 components. Since this often results in a username that is not
617 very useful, it will print a warning if it has to do this.
619 If all of these mechanisms fail, Mercurial will fail, printing an
620 error message. In this case, it will not let you commit until you set
623 You should think of the HGUSER environment variable and the -u option
624 to the “hg commit” command as ways to override Mercurial’s default
625 selection of username. For normal use, the simplest and most robust
626 way to set a username for yourself is by creating a .hgrc file; see
629 ##### Creating a Mercurial configuration file
631 To set a user name, use your favourite editor to create a file called
632 .hgrc in your home directory. Mercurial will use this file to look up
633 your personalised configuration settings. The initial contents of your
634 .hgrc should look like this.
636 # This is a Mercurial configuration file.
638 username = Firstname Lastname <email.address@domain.net>
640 The “[ui]” line begins a section of the config file, so you can read
641 the “username = ...” line as meaning “set the value of the username
642 item in the ui section”. A section continues until a new section
643 begins, or the end of the file. Mercurial ignores empty lines and
644 treats any text from “#” to the end of a line as a comment.
646 ##### Choosing a user name
648 You can use any text you like as the value of the username config
649 item, since this information is for reading by other people, but for
650 interpreting by Mercurial. The convention that most people follow is
651 to use their name and email address, as in the example above.
653 Note: Mercurial’s built-in web server obfuscates email addresses, to
654 make it more difficult for the email harvesting tools that spammers
655 use. This reduces the likelihood that you’ll start receiving more junk
656 email if you publish a Mercurial repository on the web.
658 #### 2.7.2 Writing a commit message
660 When we commit a change, Mercurial drops us into a text editor, to
661 enter a message that will describe the modifications we’ve made in
662 this changeset. This is called the commit message. It will be a record
663 for readers of what we did and why, and it will be printed by “hg log”
664 after we’ve finished committing.
668 The editor that the “hg commit” command drops us into will contain an
669 empty line, followed by a number of lines starting with “HG:”.
674 Mercurial ignores the lines that start with “HG:”; it uses them only
675 to tell us which files it’s recording changes to. Modifying or
676 deleting these lines has no effect.
678 #### 2.7.3 Writing a good commit message
680 Since “hg log” only prints the first line of a commit message by
681 default, it’s best to write a commit message whose first line stands
682 alone. Here’s a real example of a commit message that doesn’t follow
683 this guideline, and hence has a summary that is not readable.
685 changeset: 73:584af0e231be
686 user: Censored Person <censored.person@example.org>
687 date: Tue Sep 26 21:37:07 2006 -0700
688 summary: include buildmeister/commondefs. Add an exports and install
690 As far as the remainder of the contents of the commit message are
691 concerned, there are no hard-and-fast rules. Mercurial itself doesn’t
692 interpret or care about the contents of the commit message, though
693 your project may have policies that dictate a certain kind of
696 My personal preference is for short, but informative, commit messages
697 that tell me something that I can’t figure out with a quick glance at
698 the output of “hg log --patch”.
700 #### 2.7.4 Aborting a commit
702 If you decide that you don’t want to commit while in the middle of
703 editing a commit message, simply exit from your editor without saving
704 the file that it’s editing. This will cause nothing to happen to
705 either the repository or the working directory.
707 If we run the “hg commit” command without any arguments, it records
708 all of the changes we’ve made, as reported by “hg status” and “hg
711 #### 2.7.5 Admiring our new handiwork
713 Once we’ve finished the commit, we can use the “hg tip” command to
714 display the changeset we just created. This command produces output
715 that is identical to “hg log”, but it only displays the newest
716 revision in the repository.
719 changeset: 5:fa1321bf0c80
721 user: Bryan O'Sullivan <bos@serpentine.com>
722 date: Sun Jun 17 18:05:50 2007 +0000
725 Added an extra line of output
728 diff -r b57f9a090b62 -r fa1321bf0c80 hello.c
729 --- a/hello.c Tue Sep 06 15:43:07 2005 -0700
730 +++ b/hello.c Sun Jun 17 18:05:50 2007 +0000
731 @@ -8,5 +8,6 @@ int main(int argc, char ⋆⋆argv)
732 int main(int argc, char ⋆⋆argv)
734 printf("hello, world!∖");
735 + printf("hello again!∖n");
740 We refer to the newest revision in the repository as the tip revision,
743 ### 2.8 Sharing changes
745 We mentioned earlier that repositories in Mercurial are
746 self-contained. This means that the changeset we just created exists
747 only in our my-hello repository. Let’s look at a few ways that we can
748 propagate this change into other repositories.
750 #### 2.8.1 Pulling changes from another repository
752 To get started, let’s clone our original hello repository, which does
753 not contain the change we just committed. We’ll call our temporary
754 repository hello-pull.
757 $ hg clone hello hello-pull
758 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
760 We’ll use the “hg pull” command to bring changes from my-hello into
761 hello-pull. However, blindly pulling unknown changes into a repository
762 is a somewhat scary prospect. Mercurial provides the “hg incoming”
763 command to tell us what changes the “hg pull” command would pull into
764 the repository, without actually pulling the changes in.
767 $ hg incoming ../my-hello
768 comparing with ../my-hello
769 searching for changes
770 changeset: 5:fa1321bf0c80
772 user: Bryan O'Sullivan <bos@serpentine.com>
773 date: Sun Jun 17 18:05:50 2007 +0000
774 summary: Added an extra line of output
777 (Of course, someone could cause more changesets to appear in the
778 repository that we ran “hg incoming” in, before we get a chance to “hg
779 pull” the changes, so that we could end up pulling changes that we
782 Bringing changes into a repository is a simple matter of running the
783 “hg pull” command, and telling it which repository to pull from.
786 changeset: 4:b57f9a090b62
788 user: Bryan O'Sullivan <bos@serpentine.com>
789 date: Tue Sep 06 15:43:07 2005 -0700
790 summary: Trim comments.
792 $ hg pull ../my-hello
793 pulling from ../my-hello
794 searching for changes
798 added 1 changesets with 1 changes to 1 files
799 (run 'hg update' to get a working copy)
801 changeset: 5:fa1321bf0c80
803 user: Bryan O'Sullivan <bos@serpentine.com>
804 date: Sun Jun 17 18:05:50 2007 +0000
805 summary: Added an extra line of output
808 As you can see from the before-and-after output of “hg tip”, we have
809 successfully pulled changes into our repository. There remains one
810 step before we can see these changes in the working directory.
812 #### 2.8.2 Updating the working directory
814 We have so far glossed over the relationship between a repository and
815 its working directory. The “hg pull” command that we ran in
816 section [2.8.1][12] brought changes into the repository, but if we
817 check, there’s no sign of those changes in the working directory. This
818 is because “hg pull” does not (by default) touch the working
819 directory. Instead, we use the “hg update” command to do this.
821 $ grep printf hello.c
822 printf("hello, world!∖");
824 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
825 $ grep printf hello.c
826 printf("hello, world!∖");
827 printf("hello again!∖n");
829 It might seem a bit strange that “hg pull” doesn’t update the working
830 directory automatically. There’s actually a good reason for this: you
831 can use “hg update” to update the working directory to the state it
832 was in at any revision in the history of the repository. If you had
833 the working directory updated to an old revision—to hunt down the
834 origin of a bug, say—and ran a “hg pull” which automatically updated
835 the working directory to a new revision, you might not be terribly
838 However, since pull-then-update is such a common thing to do,
839 Mercurial lets you combine the two by passing the -u option to “hg
844 If you look back at the output of “hg pull” in section [2.8.1][12]
845 when we ran it without -u, you can see that it printed a helpful
846 reminder that we’d have to take an explicit step to update the working
849 (run 'hg update' to get a working copy)
851 To find out what revision the working directory is at, use the “hg
855 changeset: 5:fa1321bf0c80
857 user: Bryan O'Sullivan <bos@serpentine.com>
858 date: Sun Jun 17 18:05:50 2007 +0000
859 summary: Added an extra line of output
862 If you look back at figure [2.1][8], you’ll see arrows connecting each
863 changeset. The node that the arrow leads from in each case is a
864 parent, and the node that the arrow leads to is its child. The working
865 directory has a parent in just the same way; this is the changeset
866 that the working directory currently contains.
868 To update the working directory to a particular revision, give a
869 revision number or changeset ID to the “hg update” command.
872 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
874 changeset: 2:057d3c2d823c
875 user: Bryan O'Sullivan <bos@serpentine.com>
876 date: Tue Sep 06 13:15:43 2005 -0700
877 summary: Introduce a typo into hello.c.
880 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
882 If you omit an explicit revision, “hg update” will update to the tip
883 revision, as shown by the second call to “hg update” in the example
886 #### 2.8.3 Pushing changes to another repository
888 Mercurial lets us push changes to another repository, from the
889 repository we’re currently visiting. As with the example of “hg pull”
890 above, we’ll create a temporary repository to push our changes into.
893 $ hg clone hello hello-push
894 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
896 The “hg outgoing” command tells us what changes would be pushed into
900 $ hg outgoing ../hello-push
901 comparing with ../hello-push
902 searching for changes
903 changeset: 5:fa1321bf0c80
905 user: Bryan O'Sullivan <bos@serpentine.com>
906 date: Sun Jun 17 18:05:50 2007 +0000
907 summary: Added an extra line of output
910 And the “hg push” command does the actual push.
912 $ hg push ../hello-push
913 pushing to ../hello-push
914 searching for changes
918 added 1 changesets with 1 changes to 1 files
920 As with “hg pull”, the “hg push” command does not update the working
921 directory in the repository that it’s pushing changes into. (Unlike
922 “hg pull”, “hg push” does not provide a -u option that updates the
923 other repository’s working directory.)
925 What happens if we try to pull or push changes and the receiving
926 repository already has those changes? Nothing too exciting.
928 $ hg push ../hello-push
929 pushing to ../hello-push
930 searching for changes
933 #### 2.8.4 Sharing changes over a network
935 The commands we have covered in the previous few sections are not
936 limited to working with local repositories. Each works in exactly the
937 same fashion over a network connection; simply pass in a URL instead
940 $ hg outgoing http://hg.serpentine.com/tutorial/hello
941 comparing with http://hg.serpentine.com/tutorial/hello
942 searching for changes
943 changeset: 5:fa1321bf0c80
945 user: Bryan O'Sullivan <bos@serpentine.com>
946 date: Sun Jun 17 18:05:50 2007 +0000
947 summary: Added an extra line of output
950 In this example, we can see what changes we could push to the remote
951 repository, but the repository is understandably not set up to let
952 anonymous users push to it.
954 $ hg push http://hg.serpentine.com/tutorial/hello
955 pushing to http://hg.serpentine.com/tutorial/hello
956 searching for changes
959 [1]: http://hgbook.red-bean.com/hgbookch3.html
960 [2]: http://hgbook.red-bean.com/hgbookch1.html
961 [3]: http://hgbook.red-bean.com/hgbookch1.html#tailhgbookch1.html
962 [4]: #tailhgbookch2.html
963 [5]: http://hgbook.red-bean.com/hgbook.html#hgbookch2.html
964 [6]: http://mercurial.berkwood.com/
965 [7]: http://hgbook.red-bean.com/hgbookli4.html#Xweb:macpython
967 [9]: hgbookch2_files/tour-history.png
968 [10]: http://hgbook.red-bean.com/hgbookch12.html#x16-27100012.4
971 [13]: http://hgbook.red-bean.com/hgbookch2.html
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