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diff --git a/Documentation/tutorial-2.txt b/Documentation/tutorial-2.txt deleted file mode 100644 index af8d43bd12..0000000000 --- a/Documentation/tutorial-2.txt +++ /dev/null @@ -1,403 +0,0 @@ -A tutorial introduction to git: part two -======================================== - -You should work through link:tutorial.html[A tutorial introduction to -git] before reading this tutorial. - -The goal of this tutorial is to introduce two fundamental pieces of -git's architecture--the object database and the index file--and to -provide the reader with everything necessary to understand the rest -of the git documentation. - -The git object database ------------------------ - -Let's start a new project and create a small amount of history: - ------------------------------------------------- -$ mkdir test-project -$ cd test-project -$ git init -Initialized empty Git repository in .git/ -$ echo 'hello world' > file.txt -$ git add . -$ git commit -a -m "initial commit" -Created initial commit 54196cc2703dc165cbd373a65a4dcf22d50ae7f7 - create mode 100644 file.txt -$ echo 'hello world!' >file.txt -$ git commit -a -m "add emphasis" -Created commit c4d59f390b9cfd4318117afde11d601c1085f241 ------------------------------------------------- - -What are the 40 digits of hex that git responded to the commit with? - -We saw in part one of the tutorial that commits have names like this. -It turns out that every object in the git history is stored under -such a 40-digit hex name. That name is the SHA1 hash of the object's -contents; among other things, this ensures that git will never store -the same data twice (since identical data is given an identical SHA1 -name), and that the contents of a git object will never change (since -that would change the object's name as well). - -It is expected that the content of the commit object you created while -following the example above generates a different SHA1 hash than -the one shown above because the commit object records the time when -it was created and the name of the person performing the commit. - -We can ask git about this particular object with the cat-file -command. Don't copy the 40 hex digits from this example but use those -from your own version. Note that you can shorten it to only a few -characters to save yourself typing all 40 hex digits: - ------------------------------------------------- -$ git-cat-file -t 54196cc2 -commit -$ git-cat-file commit 54196cc2 -tree 92b8b694ffb1675e5975148e1121810081dbdffe -author J. Bruce Fields <bfields@puzzle.fieldses.org> 1143414668 -0500 -committer J. Bruce Fields <bfields@puzzle.fieldses.org> 1143414668 -0500 - -initial commit ------------------------------------------------- - -A tree can refer to one or more "blob" objects, each corresponding to -a file. In addition, a tree can also refer to other tree objects, -thus creating a directory hierarchy. You can examine the contents of -any tree using ls-tree (remember that a long enough initial portion -of the SHA1 will also work): - ------------------------------------------------- -$ git ls-tree 92b8b694 -100644 blob 3b18e512dba79e4c8300dd08aeb37f8e728b8dad file.txt ------------------------------------------------- - -Thus we see that this tree has one file in it. The SHA1 hash is a -reference to that file's data: - ------------------------------------------------- -$ git cat-file -t 3b18e512 -blob ------------------------------------------------- - -A "blob" is just file data, which we can also examine with cat-file: - ------------------------------------------------- -$ git cat-file blob 3b18e512 -hello world ------------------------------------------------- - -Note that this is the old file data; so the object that git named in -its response to the initial tree was a tree with a snapshot of the -directory state that was recorded by the first commit. - -All of these objects are stored under their SHA1 names inside the git -directory: - ------------------------------------------------- -$ find .git/objects/ -.git/objects/ -.git/objects/pack -.git/objects/info -.git/objects/3b -.git/objects/3b/18e512dba79e4c8300dd08aeb37f8e728b8dad -.git/objects/92 -.git/objects/92/b8b694ffb1675e5975148e1121810081dbdffe -.git/objects/54 -.git/objects/54/196cc2703dc165cbd373a65a4dcf22d50ae7f7 -.git/objects/a0 -.git/objects/a0/423896973644771497bdc03eb99d5281615b51 -.git/objects/d0 -.git/objects/d0/492b368b66bdabf2ac1fd8c92b39d3db916e59 -.git/objects/c4 -.git/objects/c4/d59f390b9cfd4318117afde11d601c1085f241 ------------------------------------------------- - -and the contents of these files is just the compressed data plus a -header identifying their length and their type. The type is either a -blob, a tree, a commit, or a tag. - -The simplest commit to find is the HEAD commit, which we can find -from .git/HEAD: - ------------------------------------------------- -$ cat .git/HEAD -ref: refs/heads/master ------------------------------------------------- - -As you can see, this tells us which branch we're currently on, and it -tells us this by naming a file under the .git directory, which itself -contains a SHA1 name referring to a commit object, which we can -examine with cat-file: - ------------------------------------------------- -$ cat .git/refs/heads/master -c4d59f390b9cfd4318117afde11d601c1085f241 -$ git cat-file -t c4d59f39 -commit -$ git cat-file commit c4d59f39 -tree d0492b368b66bdabf2ac1fd8c92b39d3db916e59 -parent 54196cc2703dc165cbd373a65a4dcf22d50ae7f7 -author J. Bruce Fields <bfields@puzzle.fieldses.org> 1143418702 -0500 -committer J. Bruce Fields <bfields@puzzle.fieldses.org> 1143418702 -0500 - -add emphasis ------------------------------------------------- - -The "tree" object here refers to the new state of the tree: - ------------------------------------------------- -$ git ls-tree d0492b36 -100644 blob a0423896973644771497bdc03eb99d5281615b51 file.txt -$ git cat-file blob a0423896 -hello world! ------------------------------------------------- - -and the "parent" object refers to the previous commit: - ------------------------------------------------- -$ git-cat-file commit 54196cc2 -tree 92b8b694ffb1675e5975148e1121810081dbdffe -author J. Bruce Fields <bfields@puzzle.fieldses.org> 1143414668 -0500 -committer J. Bruce Fields <bfields@puzzle.fieldses.org> 1143414668 -0500 - -initial commit ------------------------------------------------- - -The tree object is the tree we examined first, and this commit is -unusual in that it lacks any parent. - -Most commits have only one parent, but it is also common for a commit -to have multiple parents. In that case the commit represents a -merge, with the parent references pointing to the heads of the merged -branches. - -Besides blobs, trees, and commits, the only remaining type of object -is a "tag", which we won't discuss here; refer to gitlink:git-tag[1] -for details. - -So now we know how git uses the object database to represent a -project's history: - - * "commit" objects refer to "tree" objects representing the - snapshot of a directory tree at a particular point in the - history, and refer to "parent" commits to show how they're - connected into the project history. - * "tree" objects represent the state of a single directory, - associating directory names to "blob" objects containing file - data and "tree" objects containing subdirectory information. - * "blob" objects contain file data without any other structure. - * References to commit objects at the head of each branch are - stored in files under .git/refs/heads/. - * The name of the current branch is stored in .git/HEAD. - -Note, by the way, that lots of commands take a tree as an argument. -But as we can see above, a tree can be referred to in many different -ways--by the SHA1 name for that tree, by the name of a commit that -refers to the tree, by the name of a branch whose head refers to that -tree, etc.--and most such commands can accept any of these names. - -In command synopses, the word "tree-ish" is sometimes used to -designate such an argument. - -The index file --------------- - -The primary tool we've been using to create commits is "git commit --a", which creates a commit including every change you've made to -your working tree. But what if you want to commit changes only to -certain files? Or only certain changes to certain files? - -If we look at the way commits are created under the cover, we'll see -that there are more flexible ways creating commits. - -Continuing with our test-project, let's modify file.txt again: - ------------------------------------------------- -$ echo "hello world, again" >>file.txt ------------------------------------------------- - -but this time instead of immediately making the commit, let's take an -intermediate step, and ask for diffs along the way to keep track of -what's happening: - ------------------------------------------------- -$ git diff ---- a/file.txt -+++ b/file.txt -@@ -1 +1,2 @@ - hello world! -+hello world, again -$ git add file.txt -$ git diff ------------------------------------------------- - -The last diff is empty, but no new commits have been made, and the -head still doesn't contain the new line: - ------------------------------------------------- -$ git-diff HEAD -diff --git a/file.txt b/file.txt -index a042389..513feba 100644 ---- a/file.txt -+++ b/file.txt -@@ -1 +1,2 @@ - hello world! -+hello world, again ------------------------------------------------- - -So "git diff" is comparing against something other than the head. -The thing that it's comparing against is actually the index file, -which is stored in .git/index in a binary format, but whose contents -we can examine with ls-files: - ------------------------------------------------- -$ git ls-files --stage -100644 513feba2e53ebbd2532419ded848ba19de88ba00 0 file.txt -$ git cat-file -t 513feba2 -blob -$ git cat-file blob 513feba2 -hello world! -hello world, again ------------------------------------------------- - -So what our "git add" did was store a new blob and then put -a reference to it in the index file. If we modify the file again, -we'll see that the new modifications are reflected in the "git-diff" -output: - ------------------------------------------------- -$ echo 'again?' >>file.txt -$ git diff -index 513feba..ba3da7b 100644 ---- a/file.txt -+++ b/file.txt -@@ -1,2 +1,3 @@ - hello world! - hello world, again -+again? ------------------------------------------------- - -With the right arguments, git diff can also show us the difference -between the working directory and the last commit, or between the -index and the last commit: - ------------------------------------------------- -$ git diff HEAD -diff --git a/file.txt b/file.txt -index a042389..ba3da7b 100644 ---- a/file.txt -+++ b/file.txt -@@ -1 +1,3 @@ - hello world! -+hello world, again -+again? -$ git diff --cached -diff --git a/file.txt b/file.txt -index a042389..513feba 100644 ---- a/file.txt -+++ b/file.txt -@@ -1 +1,2 @@ - hello world! -+hello world, again ------------------------------------------------- - -At any time, we can create a new commit using "git commit" (without -the -a option), and verify that the state committed only includes the -changes stored in the index file, not the additional change that is -still only in our working tree: - ------------------------------------------------- -$ git commit -m "repeat" -$ git diff HEAD -diff --git a/file.txt b/file.txt -index 513feba..ba3da7b 100644 ---- a/file.txt -+++ b/file.txt -@@ -1,2 +1,3 @@ - hello world! - hello world, again -+again? ------------------------------------------------- - -So by default "git commit" uses the index to create the commit, not -the working tree; the -a option to commit tells it to first update -the index with all changes in the working tree. - -Finally, it's worth looking at the effect of "git add" on the index -file: - ------------------------------------------------- -$ echo "goodbye, world" >closing.txt -$ git add closing.txt ------------------------------------------------- - -The effect of the "git add" was to add one entry to the index file: - ------------------------------------------------- -$ git ls-files --stage -100644 8b9743b20d4b15be3955fc8d5cd2b09cd2336138 0 closing.txt -100644 513feba2e53ebbd2532419ded848ba19de88ba00 0 file.txt ------------------------------------------------- - -And, as you can see with cat-file, this new entry refers to the -current contents of the file: - ------------------------------------------------- -$ git cat-file blob 8b9743b2 -goodbye, world ------------------------------------------------- - -The "status" command is a useful way to get a quick summary of the -situation: - ------------------------------------------------- -$ git status -# On branch master -# Changes to be committed: -# (use "git reset HEAD <file>..." to unstage) -# -# new file: closing.txt -# -# Changed but not updated: -# (use "git add <file>..." to update what will be committed) -# -# modified: file.txt -# ------------------------------------------------- - -Since the current state of closing.txt is cached in the index file, -it is listed as "Changes to be committed". Since file.txt has -changes in the working directory that aren't reflected in the index, -it is marked "changed but not updated". At this point, running "git -commit" would create a commit that added closing.txt (with its new -contents), but that didn't modify file.txt. - -Also, note that a bare "git diff" shows the changes to file.txt, but -not the addition of closing.txt, because the version of closing.txt -in the index file is identical to the one in the working directory. - -In addition to being the staging area for new commits, the index file -is also populated from the object database when checking out a -branch, and is used to hold the trees involved in a merge operation. -See the link:core-tutorial.html[core tutorial] and the relevant man -pages for details. - -What next? ----------- - -At this point you should know everything necessary to read the man -pages for any of the git commands; one good place to start would be -with the commands mentioned in link:everyday.html[Everyday git]. You -should be able to find any unknown jargon in the -link:glossary.html[Glossary]. - -The link:cvs-migration.html[CVS migration] document explains how to -import a CVS repository into git, and shows how to use git in a -CVS-like way. - -For some interesting examples of git use, see the -link:howto-index.html[howtos]. - -For git developers, the link:core-tutorial.html[Core tutorial] goes -into detail on the lower-level git mechanisms involved in, for -example, creating a new commit. |