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4 A tour of Mercurial: the basics
6 ### 2.1 Installing Mercurial on your system
8 Prebuilt binary packages of Mercurial are available for every popular operating system. These make it easy to start using Mercurial on your computer immediately.
12 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 the person is who maintains the package for your distribution.
14 To keep things simple, I will focus on installing Mercurial 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.
18 1 apt-get install mercurial
22 1 yum install mercurial
30 1 yum install mercurial
32 * Ubuntu Ubuntu’s Mercurial package is based on Debian’s. To install it, run the following command.
34 1 apt-get install mercurial
36 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.
44 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.
48 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”.
50 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.
52 ### 2.2 Getting started
54 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.
57 2 Mercurial Distributed SCM (version 2937d0dbfab0)
59 4 Copyright (C) 2005, 2006 Matt Mackall <mpm@selenic.com>
60 5 This is free software; see the source for copying conditions. There is NO
61 6 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
63 #### 2.2.1 Built-in help
65 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.
68 2 hg init [-e CMD] [--remotecmd CMD] [DEST]
70 4 create a new repository in the given directory
72 6 Initialize a new repository in the given directory. If the given
73 7 directory does not exist, it is created.
75 9 If no directory is given, the current directory is used.
77 11 It is possible to specify an ssh:// URL as the destination.
78 12 Look at the help text for the pull command for important details
83 17 -e --ssh specify ssh command to use
84 18 --remotecmd specify hg command to run on the remote side
86 20 use "hg -v help init" to show global options
88 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.
90 ### 2.3 Working with a repository
92 In Mercurial, 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.
94 There’s nothing particularly magical about a repository; it is simply a directory tree in your filesystem that Mercurial treats as special. You can rename or delete a repository any time you like, using either the command line or your file browser.
96 #### 2.3.1 Making a local copy of a repository
98 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.
100 1 $ hg clone http://hg.serpentine.com/tutorial/hello
101 2 destination directory: hello
102 3 requesting all changes
105 6 adding file changes
106 7 added 5 changesets with 5 changes to 2 files
107 8 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
109 If our clone succeeded, we should now have a local directory called hello. This directory will contain some files.
113 3 drwxrwxr-x 3 bos bos 4096 Jun 17 18:05 hello
117 These files have the same contents and history in our repository as they do in the repository we cloned.
119 Every Mercurial 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, or any other, unless you tell it to.
121 What this means for now is that we’re free to experiment with our repository, safe in the knowledge that it’s a private “sandbox” that won’t affect anyone else.
123 #### 2.3.2 What’s in a repository?
125 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 of its metadata for the repository.
129 3 . .. .hg Makefile hello.c
131 The contents of the .hg directory and its subdirectories are private to Mercurial. Every other file and directory in the repository is yours to do with as you please.
133 To introduce a little terminology, the .hg 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 project, while the working directory contains a snapshot of your project at a particular point in history.
135 ### 2.4 A tour through history
137 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 view of history.
140 2 changeset: 4:b57f9a090b62
142 4 user: Bryan O'Sullivan <bos@serpentine.com>
143 5 date: Tue Sep 06 15:43:07 2005 -0700
144 6 summary: Trim comments.
146 8 changeset: 3:ff5d7b70a2a9
147 9 user: Bryan O'Sullivan <bos@serpentine.com>
148 10 date: Tue Sep 06 13:15:58 2005 -0700
149 11 summary: Get make to generate the final binary from a .o file.
151 13 changeset: 2:057d3c2d823c
152 14 user: Bryan O'Sullivan <bos@serpentine.com>
153 15 date: Tue Sep 06 13:15:43 2005 -0700
154 16 summary: Introduce a typo into hello.c.
156 18 changeset: 1:82e55d328c8c
157 19 user: mpm@selenic.com
158 20 date: Fri Aug 26 01:21:28 2005 -0700
159 21 summary: Create a makefile
161 23 changeset: 0:0a04b987be5a
162 24 user: mpm@selenic.com
163 25 date: Fri Aug 26 01:20:50 2005 -0700
164 26 summary: Create a standard "hello, world" program
167 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.
169 The fields in a record of output from “hg log” are as follows.
171 * 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.
172 * 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.
173 * 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.)
174 * summary The first line of the text message that the creator of the changeset entered to describe the changeset.
176 The default output printed by “hg log” is purely a summary; it is missing a lot of detail.
178 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.
186 Graphical history of the hello repository
190 #### 2.4.1 Changesets, revisions, and talking to other people
192 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”.
194 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.
196 * The revision number is only valid in that repository,
197 * while the hex string is the permanent, unchanging identifier that will always identify that exact changeset in every copy of the repository.
199 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.
201 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.
203 #### 2.4.2 Viewing specific revisions
205 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.
208 2 changeset: 3:ff5d7b70a2a9
209 3 user: Bryan O'Sullivan <bos@serpentine.com>
210 4 date: Tue Sep 06 13:15:58 2005 -0700
211 5 summary: Get make to generate the final binary from a .o file.
213 7 $ hg log -r ff5d7b70a2a9
214 8 changeset: 3:ff5d7b70a2a9
215 9 user: Bryan O'Sullivan <bos@serpentine.com>
216 10 date: Tue Sep 06 13:15:58 2005 -0700
217 11 summary: Get make to generate the final binary from a .o file.
219 13 $ hg log -r 1 -r 4
220 14 changeset: 1:82e55d328c8c
221 15 user: mpm@selenic.com
222 16 date: Fri Aug 26 01:21:28 2005 -0700
223 17 summary: Create a makefile
225 19 changeset: 4:b57f9a090b62
227 21 user: Bryan O'Sullivan <bos@serpentine.com>
228 22 date: Tue Sep 06 15:43:07 2005 -0700
229 23 summary: Trim comments.
232 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”.
235 2 changeset: 2:057d3c2d823c
236 3 user: Bryan O'Sullivan <bos@serpentine.com>
237 4 date: Tue Sep 06 13:15:43 2005 -0700
238 5 summary: Introduce a typo into hello.c.
240 7 changeset: 3:ff5d7b70a2a9
241 8 user: Bryan O'Sullivan <bos@serpentine.com>
242 9 date: Tue Sep 06 13:15:58 2005 -0700
243 10 summary: Get make to generate the final binary from a .o file.
245 12 changeset: 4:b57f9a090b62
247 14 user: Bryan O'Sullivan <bos@serpentine.com>
248 15 date: Tue Sep 06 15:43:07 2005 -0700
249 16 summary: Trim comments.
252 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.
254 #### 2.4.3 More detailed information
256 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.
259 2 changeset: 3:ff5d7b70a2a9
260 3 user: Bryan O'Sullivan <bos@serpentine.com>
261 4 date: Tue Sep 06 13:15:58 2005 -0700
264 7 Get make to generate the final binary from a .o file.
268 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).
270 1 $ hg log -v -p -r 2
271 2 changeset: 2:057d3c2d823c
272 3 user: Bryan O'Sullivan <bos@serpentine.com>
273 4 date: Tue Sep 06 13:15:43 2005 -0700
276 7 Introduce a typo into hello.c.
279 10 diff -r 82e55d328c8c -r 057d3c2d823c hello.c
280 11 --- a/hello.c Fri Aug 26 01:21:28 2005 -0700
281 12 +++ b/hello.c Tue Sep 06 13:15:43 2005 -0700
284 15 int main(int argc, char ⋆⋆argv)
286 17 - printf("hello, world!∖n");
287 18 + printf("hello, world!∖");
292 ### 2.5 All about command options
294 Let’s take a brief break from exploring Mercurial 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.
296 Mercurial 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.
298 * Every option has a long name. For example, as we’ve already seen, the “hg log” command accepts a --rev option.
299 * 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.)
300 * Long options start with two dashes (e.g. --rev), while short options start with one (e.g. -r).
301 * 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.
303 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.
305 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).
307 ### 2.6 Making and reviewing changes
309 Now that we have a grasp of viewing history in Mercurial, let’s take a look at making some changes and examining them.
311 The first thing we’ll do is isolate our experiment in a repository of its own. We use the “hg clone” command, but we don’t need to clone a copy of the remote repository. Since we already have a copy of it locally, we can just clone that instead. This is much faster than cloning over the network, and cloning a local repository uses less disk space in most cases, too.
314 2 $ hg clone hello my-hello
315 3 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
318 As an aside, it’s often good practice to keep a “pristine” copy of a remote repository around, which you can then make temporary clones of to create sandboxes for each task you want to work on. This lets you work on multiple tasks in parallel, each isolated from the others until it’s complete and you’re ready to integrate it back. Because local clones are so cheap, there’s almost no overhead to cloning and destroying repositories whenever you want.
320 In our my-hello repository, we have a file hello.c that contains the classic “hello, world” program. Let’s use the ancient and venerable sed command to edit this file so that it prints a second line of output. (I’m only using sed to do this because it’s easy to write a scripted example this way. Since you’re not under the same constraint, you probably won’t want to use sed; simply use your preferred text editor to do the same thing.)
322 1 $ sed -i '/printf/a∖∖tprintf("hello again!∖∖n");' hello.c
324 Mercurial’s “hg status” command will tell us what Mercurial knows about the files in the repository.
331 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.
333 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.
335 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.
338 2 diff -r b57f9a090b62 hello.c
339 3 --- a/hello.c Tue Sep 06 15:43:07 2005 -0700
340 4 +++ b/hello.c Sun Jun 17 18:05:50 2007 +0000
341 5 @@ -8,5 +8,6 @@ int main(int argc, char ⋆⋆argv)
342 6 int main(int argc, char ⋆⋆argv)
344 8 printf("hello, world!∖");
345 9 + printf("hello again!∖n");
349 ### 2.7 Recording changes in a new changeset
351 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 we’ve done and arrive at a natural stopping point where we want to record our work in a new changeset.
353 The “hg commit” command lets us create a new changeset; we’ll usually refer to this as “making a commit” or “committing”.
355 #### 2.7.1 Setting up a username
357 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:
359 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.
360 2. If you have set the HGUSER environment variable, this is checked next.
361 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.
362 4. If you have set the EMAIL environment variable, this will be used next.
363 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.
365 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.
367 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.
369 ##### Creating a Mercurial configuration file
371 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.
373 1 # This is a Mercurial configuration file.
375 3 username = Firstname Lastname <email.address@domain.net>
377 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.
379 ##### Choosing a user name
381 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.
383 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.
385 #### 2.7.2 Writing a commit message
387 When we commit a change, Mercurial 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” after we’ve finished committing.
391 The editor that the “hg commit” command drops us into will contain an empty line, followed by a number of lines starting with “HG:”.
394 2 HG: changed hello.c
396 Mercurial ignores the lines that start with “HG:”; it uses them only to tell us which files it’s recording changes to. Modifying or deleting these lines has no effect.
398 #### 2.7.3 Writing a good commit message
400 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 this guideline, and hence has a summary that is not readable.
402 1 changeset: 73:584af0e231be
403 2 user: Censored Person <censored.person@example.org>
404 3 date: Tue Sep 26 21:37:07 2006 -0700
405 4 summary: include buildmeister/commondefs. Add an exports and install
407 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 interpret or care about the contents of the commit message, though your project may have policies that dictate a certain kind of formatting.
409 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”.
411 #### 2.7.4 Aborting a commit
413 If you decide that you don’t want to commit while in the middle of editing a commit message, simply exit from your editor without saving the file that it’s editing. This will cause nothing to happen to either the repository or the working directory.
415 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”.
417 #### 2.7.5 Admiring our new handiwork
419 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.
422 2 changeset: 5:fa1321bf0c80
424 4 user: Bryan O'Sullivan <bos@serpentine.com>
425 5 date: Sun Jun 17 18:05:50 2007 +0000
428 8 Added an extra line of output
431 11 diff -r b57f9a090b62 -r fa1321bf0c80 hello.c
432 12 --- a/hello.c Tue Sep 06 15:43:07 2005 -0700
433 13 +++ b/hello.c Sun Jun 17 18:05:50 2007 +0000
434 14 @@ -8,5 +8,6 @@ int main(int argc, char ⋆⋆argv)
435 15 int main(int argc, char ⋆⋆argv)
437 17 printf("hello, world!∖");
438 18 + printf("hello again!∖n");
443 We refer to the newest revision in the repository as the tip revision, or simply the tip.
445 ### 2.8 Sharing changes
447 We mentioned earlier that repositories in Mercurial are self-contained. This means that the changeset we just created exists only in our my-hello repository. Let’s look at a few ways that we can propagate this change into other repositories.
449 #### 2.8.1 Pulling changes from another repository
451 To get started, let’s clone our original hello repository, which does not contain the change we just committed. We’ll call our temporary repository hello-pull.
454 2 $ hg clone hello hello-pull
455 3 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
457 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.
460 2 $ hg incoming ../my-hello
461 3 comparing with ../my-hello
462 4 searching for changes
463 5 changeset: 5:fa1321bf0c80
465 7 user: Bryan O'Sullivan <bos@serpentine.com>
466 8 date: Sun Jun 17 18:05:50 2007 +0000
467 9 summary: Added an extra line of output
470 (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.)
472 Bringing changes into a repository is a simple matter of running the “hg pull” command, and telling it which repository to pull from.
475 2 changeset: 4:b57f9a090b62
477 4 user: Bryan O'Sullivan <bos@serpentine.com>
478 5 date: Tue Sep 06 15:43:07 2005 -0700
479 6 summary: Trim comments.
481 8 $ hg pull ../my-hello
482 9 pulling from ../my-hello
483 10 searching for changes
486 13 adding file changes
487 14 added 1 changesets with 1 changes to 1 files
488 15 (run 'hg update' to get a working copy)
490 17 changeset: 5:fa1321bf0c80
492 19 user: Bryan O'Sullivan <bos@serpentine.com>
493 20 date: Sun Jun 17 18:05:50 2007 +0000
494 21 summary: Added an extra line of output
497 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.
499 #### 2.8.2 Updating the working directory
501 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.
503 1 $ grep printf hello.c
504 2 printf("hello, world!∖");
506 4 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
507 5 $ grep printf hello.c
508 6 printf("hello, world!∖");
509 7 printf("hello again!∖n");
511 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.
513 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”.
517 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:
519 1 (run 'hg update' to get a working copy)
521 To find out what revision the working directory is at, use the “hg parents” command.
524 2 changeset: 5:fa1321bf0c80
526 4 user: Bryan O'Sullivan <bos@serpentine.com>
527 5 date: Sun Jun 17 18:05:50 2007 +0000
528 6 summary: Added an extra line of output
531 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.
533 To update the working directory to a particular revision, give a revision number or changeset ID to the “hg update” command.
536 2 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
538 4 changeset: 2:057d3c2d823c
539 5 user: Bryan O'Sullivan <bos@serpentine.com>
540 6 date: Tue Sep 06 13:15:43 2005 -0700
541 7 summary: Introduce a typo into hello.c.
544 10 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
546 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.
548 #### 2.8.3 Pushing changes to another repository
550 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.
553 2 $ hg clone hello hello-push
554 3 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
556 The “hg outgoing” command tells us what changes would be pushed into another repository.
559 2 $ hg outgoing ../hello-push
560 3 comparing with ../hello-push
561 4 searching for changes
562 5 changeset: 5:fa1321bf0c80
564 7 user: Bryan O'Sullivan <bos@serpentine.com>
565 8 date: Sun Jun 17 18:05:50 2007 +0000
566 9 summary: Added an extra line of output
569 And the “hg push” command does the actual push.
571 1 $ hg push ../hello-push
572 2 pushing to ../hello-push
573 3 searching for changes
576 6 adding file changes
577 7 added 1 changesets with 1 changes to 1 files
579 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.)
581 What happens if we try to pull or push changes and the receiving repository already has those changes? Nothing too exciting.
583 1 $ hg push ../hello-push
584 2 pushing to ../hello-push
585 3 searching for changes
588 #### 2.8.4 Sharing changes over a network
590 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.
592 1 $ hg outgoing http://hg.serpentine.com/tutorial/hello
593 2 comparing with http://hg.serpentine.com/tutorial/hello
594 3 searching for changes
595 4 changeset: 5:fa1321bf0c80
597 6 user: Bryan O'Sullivan <bos@serpentine.com>
598 7 date: Sun Jun 17 18:05:50 2007 +0000
599 8 summary: Added an extra line of output
602 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.
604 1 $ hg push http://hg.serpentine.com/tutorial/hello
605 2 pushing to http://hg.serpentine.com/tutorial/hello
606 3 searching for changes
609 [[next][1]] [[prev][2]] [[prev-tail][3]] [[front][13]] [[up][5]]
611 [1]: http://hgbook.red-bean.com/hgbookch3.html
612 [2]: http://hgbook.red-bean.com/hgbookch1.html
613 [3]: http://hgbook.red-bean.com/hgbookch1.html#tailhgbookch1.html
614 [4]: #tailhgbookch2.html
615 [5]: http://hgbook.red-bean.com/hgbook.html#hgbookch2.html
616 [6]: http://mercurial.berkwood.com/
617 [7]: http://hgbook.red-bean.com/hgbookli4.html#Xweb:macpython
619 [9]: hgbookch2_files/tour-history.png
620 [10]: http://hgbook.red-bean.com/hgbookch12.html#x16-27100012.4
623 [13]: http://hgbook.red-bean.com/hgbookch2.html