2.2 Git ขั้นพื้นฐาน - การบันทึกการแก้ไขใน Repository

การบันทึกการแก้ไขใน Repository

หลังจากทำการคัดลอง repository และได้แฟ้มต่าง ๆ มา คุณสามารถทำการแก้ไขและ commit เพื่อจัดเก็บการแก้ไขเข้าไปใน repository เมื่อคุณต้องการ

ขอให้จำไว้ว่าแฟ้มแต่ละแฟ้มใน working directory มีสถานะอยู่สองสถานะ คือ tracked หรือ untracked แฟ้มที่อยู่ในสถานะ tracked คือแฟ้มที่อยู่ใน snapshot ล่าสุด เป็นแฟ้มที่คุณสามารถกู้เนื้อหากลับมา แก้ไข หรือ stage ได้ ส่วนแฟ้มที่อยู่ในสถานะ untracked คือแฟ้มที่ไม่อยู่ใน snapshot ล่าสุดและไม่อยู่ใน staging area หลักจากคุณ clone repository แฟ้มทั้งหมดจะอยู่ในสถานะ tracked เพราะคุณเพิ่ง check out ออกมา

เมื่อคุณทำการแก้ไข แฟ้มที่ถูกแก้ไขจะอยู่ในสถานะถูกแก้ไขเพราะเนื้อหาได้ถูกเปลี่ยนไป ถ้าคุณต้องการจัดเก็บการแก้ไข คุณต้อง stage แฟ้มเหล่านั้นและ commit สิ่งที่คุณ stage เอาไว้ ตามรูป 2-1

รูปที่ 2-1. วงจรสถานะของแฟ้ม

การตรวจสอบสถานะของแฟ้ม

เครื่องมือหลักในการตรวจสอบสถานะของแฟ้มคือคำสั่ง git status ถ้าคุณใช้คำสั่งนี้ทันทีหลังจาก clone repository คุณจะเห็นผลลัพธ์ประมาณนี้:

$ git status
# On branch master
nothing to commit, working directory clean

ผลลัพธ์ด้านบนหมายความว่าไดเรกทอรีของคุณยังสะอาดอยู่ นั่นก็คือไม่มีการแก้ไขแฟ้มที่ถูก track และ ไม่มีแฟ้มที่อยู่ในสถานะ untracked ในไดเรกทอรี นอกจากนั้นคำสั่งนี้ยังบอกว่าคุณอยู่ใน branch ชื่อ master ซึ่งเป็น branch เริ่มต้นอยู่แล้ว เราจะลงรายละเอียดเกี่ยวกับ branch และ reference ในบทถัดไป

สมมุติว่าคุณสร้างแฟ้มข้อมูลใหม่ เช่น README ซึ่งไม่เคยมีมาก่อน เมื่อคุณใช้คำสั่ง git status คุณจะเห็นสถานะของแฟ้มเป็น untracked:

$ vim README
$ git status
# On branch master
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#   README
nothing added to commit but untracked files present (use "git add" to track)

คุณจะเห็นว่าแฟ้ม README อยู่ในสถานะ untracked เพราะว่ามันอยู่ภายใต้หัวข้อ "Untracked files" ในผลลัพธ์ของคำสั่ง ความหมายของ untracked คือแฟ้มข้อมูลนี้ไม่อยู่ใน snapshot (commit) ล่าสุด และ Git จะไม่รวมแฟ้มข้อมูลนี้ใน commit ถัดไปนอกเสียจากว่าคุณบอกให้ Git ทำ เหตุผลที่ Git ทำงานแบบนี้ก็เพื่อป้องกันไม่ให้แฟ้มไบนารีหรือแฟ้มข้อมูลอื่น ๆ ถูกเพิ่มเข้าไปใน repository โดยไม่ได้ตั้งใจ ในกรณีนี้เนื่องจากคุณต้องการเพิ่มแฟ้ม README อ่านวิธีการเพิ่มแฟ้มใหม่ในส่วนถัดไปได้เลย

การเพิ่มแฟ้มข้อมูลใหม่

คุณสามารถเพิ่มแฟ้มข้อมูลใหม่โดยใช้คำสั่ง git add:

$ git add README

ถ้าคุณใช้คำสั่ง status อีกครั้ง คุณจะเห็นว่าแฟ้ม README มีสถานะเป็น tracked และถูก staged เรียบร้อย:

$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   README
#

You can tell that it’s staged because it’s under the “Changes to be committed” heading. If you commit at this point, the version of the file at the time you ran git add is what will be in the historical snapshot. You may recall that when you ran git init earlier, you then ran git add (files) — that was to begin tracking files in your directory. The git add command takes a path name for either a file or a directory; if it’s a directory, the command adds all the files in that directory recursively.

การ Stage แฟ้มที่ถูกแก้ไข

Let’s change a file that was already tracked. If you change a previously tracked file called benchmarks.rband then run your status command again, you get something that looks like this:

$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   README
#
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#
#   modified:   benchmarks.rb
#

The benchmarks.rb file appears under a section named “Changes not staged for commit” — which means that a file that is tracked has been modified in the working directory but not yet staged. To stage it, you run the git add command (it’s a multipurpose command — you use it to begin tracking new files, to stage files, and to do other things like marking merge-conflicted files as resolved). Let’s run git add now to stage the benchmarks.rb file, and then run git status again:

$ git add benchmarks.rb
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   README
#   modified:   benchmarks.rb
#

Both files are staged and will go into your next commit. At this point, suppose you remember one little change that you want to make in benchmarks.rb before you commit it. You open it again and make that change, and you’re ready to commit. However, let’s run git status one more time:

$ vim benchmarks.rb 
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   README
#   modified:   benchmarks.rb
#
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#
#   modified:   benchmarks.rb
#

What the heck? Now benchmarks.rb is listed as both staged and unstaged. How is that possible? It turns out that Git stages a file exactly as it is when you run the git add command. If you commit now, the version of benchmarks.rb as it was when you last ran the git add command is how it will go into the commit, not the version of the file as it looks in your working directory when you run git commit. If you modify a file after you run git add, you have to run git add again to stage the latest version of the file:

$ git add benchmarks.rb
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   README
#   modified:   benchmarks.rb
#

Ignoring Files

Often, you’ll have a class of files that you don’t want Git to automatically add or even show you as being untracked. These are generally automatically generated files such as log files or files produced by your build system. In such cases, you can create a file listing patterns to match them named .gitignore. Here is an example .gitignore file:

$ cat .gitignore
*.[oa]
*~

The first line tells Git to ignore any files ending in .o or .a — object and archive files that may be the product of building your code. The second line tells Git to ignore all files that end with a tilde (~), which is used by many text editors such as Emacs to mark temporary files. You may also include a log, tmp, or pid directory; automatically generated documentation; and so on. Setting up a .gitignore file before you get going is generally a good idea so you don’t accidentally commit files that you really don’t want in your Git repository.

The rules for the patterns you can put in the .gitignore file are as follows:

• Blank lines or lines starting with # are ignored.
• Standard glob patterns work.
• You can end patterns with a forward slash (/) to specify a directory.
• You can negate a pattern by starting it with an exclamation point (!).

Glob patterns are like simplified regular expressions that shells use. An asterisk (*) matches zero or more characters; [abc] matches any character inside the brackets (in this case a, b, or c); a question mark (?) matches a single character; and brackets enclosing characters separated by a hyphen([0-9]) matches any character between them (in this case 0 through 9) .

Here is another example .gitignore file:

# a comment – this is ignored
# no .a files
*.a
# but do track lib.a, even though you're ignoring .a files above
!lib.a
# only ignore the root TODO file, not subdir/TODO
/TODO
# ignore all files in the build/ directory
build/
# ignore doc/notes.txt, but not doc/server/arch.txt
doc/*.txt

Viewing Your Staged and Unstaged Changes

If the git status command is too vague for you — you want to know exactly what you changed, not just which files were changed — you can use the git diff command. We’ll cover git diff in more detail later; but you’ll probably use it most often to answer these two questions: What have you changed but not yet staged? And what have you staged that you are about to commit? Although git status answers those questions very generally, git diff shows you the exact lines added and removed — the patch, as it were.

Let’s say you edit and stage the README file again and then edit the benchmarks.rb file without staging it. If you run your status command, you once again see something like this:

$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   README
#
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#
#   modified:   benchmarks.rb
#

To see what you’ve changed but not yet staged, type git diff with no other arguments:

$ git diff
diff --git a/benchmarks.rb b/benchmarks.rb
index 3cb747f..da65585 100644
--- a/benchmarks.rb
+++ b/benchmarks.rb
@@ -36,6 +36,10 @@ def main
           @commit.parents[0].parents[0].parents[0]
         end

+        run_code(x, 'commits 1') do
+          git.commits.size
+        end
+
         run_code(x, 'commits 2') do
           log = git.commits('master', 15)
           log.size

That command compares what is in your working directory with what is in your staging area. The result tells you the changes you’ve made that you haven’t yet staged.

If you want to see what you’ve staged that will go into your next commit, you can use git diff –-cached. (In Git versions 1.6.1 and later, you can also use git diff –-staged, which may be easier to remember.) This command compares your staged changes to your last commit:

$ git diff --cached
diff --git a/README b/README
new file mode 100644
index 0000000..03902a1
--- /dev/null
+++ b/README2
@@ -0,0 +1,5 @@
+grit
+ by Tom Preston-Werner, Chris Wanstrath
+ http://github.com/mojombo/grit
+
+Grit is a Ruby library for extracting information from a Git repository

It’s important to note that git diff by itself doesn’t show all changes made since your last commit — only changes that are still unstaged. This can be confusing, because if you’ve staged all of your changes, git diff will give you no output.

For another example, if you stage the benchmarks.rb file and then edit it, you can use git diff to see the changes in the file that are staged and the changes that are unstaged:

$ git add benchmarks.rb
$ echo '# test line' >> benchmarks.rb
$ git status
# On branch master
#
# Changes to be committed:
#
#   modified:   benchmarks.rb
#
# Changes not staged for commit:
#
#   modified:   benchmarks.rb
#

Now you can use git diff to see what is still unstaged

$ git diff 
diff --git a/benchmarks.rb b/benchmarks.rb
index e445e28..86b2f7c 100644
--- a/benchmarks.rb
+++ b/benchmarks.rb
@@ -127,3 +127,4 @@ end
 main()

 ##pp Grit::GitRuby.cache_client.stats 
+# test line

and git diff --cached to see what you’ve staged so far:

$ git diff --cached
diff --git a/benchmarks.rb b/benchmarks.rb
index 3cb747f..e445e28 100644
--- a/benchmarks.rb
+++ b/benchmarks.rb
@@ -36,6 +36,10 @@ def main
          @commit.parents[0].parents[0].parents[0]
        end

+        run_code(x, 'commits 1') do
+          git.commits.size
+        end
+              
        run_code(x, 'commits 2') do
          log = git.commits('master', 15)
          log.size

Committing Your Changes

Now that your staging area is set up the way you want it, you can commit your changes. Remember that anything that is still unstaged — any files you have created or modified that you haven’t run git add on since you edited them — won’t go into this commit. They will stay as modified files on your disk. In this case, the last time you ran git status, you saw that everything was staged, so you’re ready to commit your changes. The simplest way to commit is to type git commit:

$ git commit

Doing so launches your editor of choice. (This is set by your shell’s $EDITOR environment variable — usually vim or emacs, although you can configure it with whatever you want using the git config --global core.editor command as you saw in Chapter 1).

The editor displays the following text (this example is a Vim screen):

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       new file:   README
#       modified:   benchmarks.rb 
~
~
~
".git/COMMIT_EDITMSG" 10L, 283C

You can see that the default commit message contains the latest output of the git status command commented out and one empty line on top. You can remove these comments and type your commit message, or you can leave them there to help you remember what you’re committing. (For an even more explicit reminder of what you’ve modified, you can pass the -v option to git commit. Doing so also puts the diff of your change in the editor so you can see exactly what you did.) When you exit the editor, Git creates your commit with that commit message (with the comments and diff stripped out).

Alternatively, you can type your commit message inline with the commit command by specifying it after a -m flag, like this:

$ git commit -m "Story 182: Fix benchmarks for speed"
[master]: created 463dc4f: "Fix benchmarks for speed"
 2 files changed, 3 insertions(+), 0 deletions(-)
 create mode 100644 README

Now you’ve created your first commit! You can see that the commit has given you some output about itself: which branch you committed to (master), what SHA-1 checksum the commit has (463dc4f), how many files were changed, and statistics about lines added and removed in the commit.

Remember that the commit records the snapshot you set up in your staging area. Anything you didn’t stage is still sitting there modified; you can do another commit to add it to your history. Every time you perform a commit, you’re recording a snapshot of your project that you can revert to or compare to later.

Skipping the Staging Area

Although it can be amazingly useful for crafting commits exactly how you want them, the staging area is sometimes a bit more complex than you need in your workflow. If you want to skip the staging area, Git provides a simple shortcut. Providing the -a option to the git commit command makes Git automatically stage every file that is already tracked before doing the commit, letting you skip the git add part:

$ git status
# On branch master
#
# Changes not staged for commit:
#
#   modified:   benchmarks.rb
#
$ git commit -a -m 'added new benchmarks'
[master 83e38c7] added new benchmarks
 1 files changed, 5 insertions(+), 0 deletions(-)

Notice how you don’t have to run git add on the benchmarks.rb file in this case before you commit.

Removing Files

To remove a file from Git, you have to remove it from your tracked files (more accurately, remove it from your staging area) and then commit. The git rm command does that and also removes the file from your working directory so you don’t see it as an untracked file next time around.

If you simply remove the file from your working directory, it shows up under the “Changes not staged for commit” (that is, unstaged) area of your git status output:

$ rm grit.gemspec
$ git status
# On branch master
#
# Changes not staged for commit:
#   (use "git add/rm <file>..." to update what will be committed)
#
#       deleted:    grit.gemspec
#

Then, if you run git rm, it stages the file’s removal:

$ git rm grit.gemspec
rm 'grit.gemspec'
$ git status
# On branch master
#
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       deleted:    grit.gemspec
#

The next time you commit, the file will be gone and no longer tracked. If you modified the file and added it to the index already, you must force the removal with the -f option. This is a safety feature to prevent accidental removal of data that hasn’t yet been recorded in a snapshot and that can’t be recovered from Git.

Another useful thing you may want to do is to keep the file in your working tree but remove it from your staging area. In other words, you may want to keep the file on your hard drive but not have Git track it anymore. This is particularly useful if you forgot to add something to your .gitignore file and accidentally added it, like a large log file or a bunch of .a compiled files. To do this, use the --cachedoption:

$ git rm --cached readme.txt

You can pass files, directories, and file-glob patterns to the git rm command. That means you can do things such as

$ git rm log/\*.log

Note the backslash (\) in front of the *. This is necessary because Git does its own filename expansion in addition to your shell’s filename expansion. This command removes all files that have the .log extension in the log/ directory. Or, you can do something like this:

$ git rm \*~

This command removes all files that end with ~.

Moving Files

Unlike many other VCS systems, Git doesn’t explicitly track file movement. If you rename a file in Git, no metadata is stored in Git that tells it you renamed the file. However, Git is pretty smart about figuring that out after the fact — we’ll deal with detecting file movement a bit later.

Thus it’s a bit confusing that Git has a mv command. If you want to rename a file in Git, you can run something like

$ git mv file_from file_to

and it works fine. In fact, if you run something like this and look at the status, you’ll see that Git considers it a renamed file:

$ git mv README.txt README
$ git status
# On branch master
# Your branch is ahead of 'origin/master' by 1 commit.
#
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       renamed:    README.txt -> README
#

However, this is equivalent to running something like this:

$ mv README.txt README
$ git rm README.txt
$ git add README

Git figures out that it’s a rename implicitly, so it doesn’t matter if you rename a file that way or with the mvcommand. The only real difference is that mv is one command instead of three — it’s a convenience function. More important, you can use any tool you like to rename a file, and address the add/rm later, before you commit.