### 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
- 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.
+ Trim comments.
- changeset: 2:057d3c2d823c
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:43 2005 -0700
- summary: Introduce a typo into hello.c.
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 2005 -0700
- changeset: 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: 0:0a04b987be5a
- user: mpm@selenic.com
- date: Fri Aug 26 01:20:50 2005 -0700
- summary: Create a standard "hello, world" program
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
+ Introduce a typo into hello.c.
+
+ commit 0a633bf58b45fcf1a8299d3c82cd1fd26d3f48f2
+ Author: Bryan O'Sullivan <mpm@selenic.com>
+ Date: Fri Aug 26 01:21:28 2005 -0700
+
+ Create a makefile
+
+ 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 git 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
+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
* * *
-#### 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 derived 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
- $ 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.
+ Trim comments.
- $ 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
+ commit 72d4f10e4a27dbb09ace1503c20dbac1912ee451
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:58 2005 -0700
- changeset: 4:b57f9a090b62
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 15:43:07 2005 -0700
- summary: Trim comments.
+ Get make to generate the final binary from a .o file.
+
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
+ Introduce a typo into hello.c.
-If you want to see 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”.
+#### 2.4.4 Other log filters
- $ 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.
+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:
+
+ $ 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
-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.
+And "git log" can also filter based on the dates at which commits were
+created:
+
+ $ git log --since="2 weeks ago" --until="yesterday"
+
+Another useful option is -n or --max-count which, unsurprisingly,
+limits the maximum number of commits to be displayed.
#### 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.
+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:
- $ 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.
+ $ 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
+
+ Get make to generate the final binary from a .o file.
+
+ 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 -r 82e55d328c8c -r 057d3c2d823c hello.c
- --- a/hello.c Fri Aug 26 01:21:28 2005 -0700
- +++ b/hello.c Tue Sep 06 13:15:43 2005 -0700
- @@ -11,6 +11,6 @@
+ diff --git a/hello.c b/hello.c
+ index ed55ec0..80b260c 100644
+ --- a/hello.c
+ +++ b/hello.c
+ @@ -11,6 +11,6 @@
+
+ int main(int argc, char **argv)
+ {
+ - printf("hello, world!\n");
+ + printf("hello, world!\");
+ return 0;
+ }
+
+Of course, wanting to see all this information for a single commit is
+such a common operation that it's given its own name in git, "git
+show". So "git show 13ed136b" is a much easier way to get exactly the
+same output:
+
+ $ git show 13ed136b
+ commit 13ed136b983a9c439eddeea8a1c2076cffbb685f
+ Author: Bryan O'Sullivan <bos@serpentine.com>
+ Date: Tue Sep 6 13:15:43 2005 -0700
- int main(int argc, char ⋆⋆argv)
- {
- - printf("hello, world!∖n");
- + printf("hello, world!∖");
- return 0;
- }
+ Introduce a typo into hello.c.
+ 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 /home/cworth/src/hgbook-git/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
-
-Mercurial’s “hg status” command will tell us what Mercurial knows
-about the files in the repository.
+ $ sed -i '/printf/a\\tprintf("hello again!\\n");' hello.c
- $ ls
- Makefile hello.c
- $ hg status
- M hello.c
+The “git status” command will tell us what git knows about the files
+in the repository.
-The “hg status” command prints no output for some files, but a line
-starting with “M” for hello.c. Unless you tell it to, “hg status” will
-not print any output for files that have not been modified.
-
-The “M” indicates that Mercurial has noticed that we modified
-hello.c. We didn’t need to inform Mercurial that we were going to
-modify the file before we started, or that we had modified the file
-after we were done; it was able to figure this out itself.
+ $ 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")
+
+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.
+
+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 all changes
+to tracked files. Without this, "git commit" will only commit changes
+that have been previously staged for committing with "git add
+file". The most common usage is to commit with "git commit -a" and
+only use "git add file; git commit" when there is a need to commit
+only some subset of changes that have been made.
+
+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.
+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):
- $ 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
+ $ 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
projects / hgbook-git / blobdiff