Changes for page Git

Last modified by Richard Kreissig on 2025/01/30 12:03

From version < 36.1 >

edited by msp
on 2012/10/16 14:34

To version < 43.1 >

edited by msp
on 2012/10/16 16:41

Change comment: There is no comment for this version

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@@ -2,14 +2,16 @@
  More in-depth Git documentation can be found on the [[official home page>>url:http://git-scm.com/documentation||shape="rect"]], which mentions books, videos, and links to other tutorials and references. Furthermore, the shell command {{code language="none"}}git help{{/code}} lists the most commonly used Git commands, and {{code language="none"}}git help <command>{{/code}} gives very detailed documentation for the specified Git command.
--==== Contents ====
++=== Contents ===
--{{toc style="circle" maxLevel="3"/}}
++{{toc style="circle" maxLevel="2"/}}
  = Creating Commits =
++Most steps of this tutorial are done by typing shell commands. The grey boxes contain the commands you should enter, preceded by a {{code language="none"}}${{/code}} symbol, and followed by their output. While you may copy & paste these commands, some of them may require modifications to adapt them to your own projects. The output will be slightly different for many commands when you enter them, since it also depends on parameters such as the user name and time of execution.
++
 . Read the [[Git for Computer Scientists>>url:http://eagain.net/articles/git-for-computer-scientists/||shape="rect"]] introduction (skip this if you are already familiar with Git).
 . For Linux, Git is available in its own package. Windows users can install [[msysGit>>url:http://msysgit.github.com/||shape="rect"]]. For Mac OSX, Git is available as part of [[Xcode>>url:https://developer.apple.com/xcode/||shape="rect"]]; if you cannot install that, use [[Git for OSX>>url:http://code.google.com/p/git-osx-installer/||shape="rect"]].
 . (((
@@ -126,11 +126,11 @@
  + * The head is controlled by a finite state machine
  {{/noformat}}
--Note that each commit is identified by a looong hash value, but it is possible to use only a prefix when referencing them (if the prefix is not ambiguous): the example above uses {{code language="none"}}52e2d49{{/code}} to identify the second commit. The commit hashes in your repository will be different from those seen in this tutorial, because the name of the author and the exact time of committing is also considered in the hash calculation. Also try the command {{code language="none"}}gitk{{/code}} to get an overview of your commits (a better alternative available for MacOS is [[GitX>>url:http://gitx.frim.nl/||shape="rect"]]).
++Note that each commit is identified by a looong hash value, but it is possible to use only a prefix when referencing them (if the prefix is not ambiguous): the example above uses {{code language="none"}}52e2d49{{/code}} to identify the second commit. The commit hashes in your repository will be different from those seen in this tutorial, because the name of the author and the exact time of committing is also considered in the hash calculation. Also try the command {{code language="none"}}gitk{{/code}} to get an overview of your commits (a better alternative available for Mac OSX is [[GitX>>url:http://gitx.frim.nl/||shape="rect"]]).
  = Branching and Merging =
--In the previous section you have created two commits on the default branch, which is named {{code language="none"}}master{{/code}}. Now you will create a new branch and commit there, thus adding complexity to the commit graph.
++In the previous section you have created two commits on the default branch, which is named {{code language="none"}}master{{/code}}. Now you will create a new branch and commit there, thus adding complexity to the commit graph. In general, you may create as many local branches as you like, since they are simple to use and can be a great tool to structure your work.
 . (((
  Create a branch with name //sketches//:
@@ -203,7 +203,7 @@
  {{/noformat}}
  )))
 . (((
--Switch back to the {{code language="none"}}sketches{{/code}} branch and commit something there. Note that the {{code language="none"}}checkout{{/code}} command modifies your working copy, hence you have to update your text editor's content if you opened one of the files.
++Switch back to the {{code language="none"}}sketches{{/code}} branch and modify it as shown below. Note that the {{code language="none"}}checkout{{/code}} command modifies your working copy, hence you have to update your text editor's content if you opened one of the files.
  {{noformat}}
  $ git checkout sketches
@@ -219,7 +219,7 @@
 files changed, 5 insertions(+), 0 deletions(-)
  {{/noformat}}
--Now our two branches have //diverged//, which means that they cannot be fast-forwarded anymore.
++Now your two branches have //diverged//, which means that they cannot be fast-forwarded anymore.
  )))
 . (((
  Merge the {{code language="none"}}master{{/code}} branch into {{code language="none"}}sketches{{/code}}:
@@ -243,8 +243,8 @@
   * The finite state machine has an initial state and one or more final states
  {{/noformat}}
  )))
--1. Commit the change to {{code language="none"}}notes.txt{{/code}}.
--1. Check out {{code language="none"}}sketches{{/code}} (make sure to refresh your text editor so {{code language="none"}}notes.txt{{/code}} is reset to its previous state, without the change made above).
++1. Commit the change of {{code language="none"}}notes.txt{{/code}}.
++1. Check out {{code language="none"}}sketches{{/code}} (make sure to refresh your text editor so that {{code language="none"}}notes.txt{{/code}} is reset to its previous state, without the change made above).
 . (((
  Insert the following line after line 4 of {{code language="none"}}notes.txt{{/code}}:
@@ -252,7 +252,7 @@
   * Each state transition can trigger head movement and data read/write
  {{/noformat}}
  )))
--1. Commit the change to {{code language="none"}}notes.txt{{/code}}.
++1. Commit the change of {{code language="none"}}notes.txt{{/code}}.
  )))
 . (((
  Merge the {{code language="none"}}master{{/code}} branch into the current branch ({{code language="none"}}sketches{{/code}}):
@@ -332,6 +332,8 @@
  In the previous sections you have worked only with a local repository. The next step is to share this content with a remote repository. Later we will use [[Stash>>url:https://www.atlassian.com/software/stash/overview||shape="rect"]] for repository management, but we need to create group accounts for you first, thus you will use another system called [[Gitorious>>url:https://git.rtsys.informatik.uni-kiel.de/||shape="rect"]] for now.
++Usually it is sufficient to have only one local copy of a Git repository. However, in this tutorial you will create a second copy in order to "simulate" what can happen if two users access the same remote repository: imagine the directories {{code language="none"}}turing{{/code}} and {{code language="none"}}turing2{{/code}} are each managed by a different user. You will simulate the resulting interference by switching your working directory between these two.
++
 . Register to the Gitorious system: [[https:~~/~~/git.rtsys.informatik.uni-kiel.de/>>url:https://git.rtsys.informatik.uni-kiel.de/||shape="rect"]] (use your //Institut für Informatik// login name and email address)
 . Go to your //Dashboard// → //Manage SSH keys// → //Add SSH key//
 . Copy & paste the content of your public SSH key.\\
@@ -338,7 +338,8 @@
 *. If you don't have an SSH key: use the shell command {{code language="none"}}ssh-keygen{{/code}}, confirm the default destination file {{code language="none"}}~/.ssh/id_rsa{{/code}}, and choose whether to give a passphrase. If you have a passphrase, you need to enter it whenever you use your SSH key for the first time in a session. You can omit the passphrase, but that makes the key less secure. As result, the tool generates a private key {{code language="none"}}~/.ssh/id_rsa{{/code}}, which has to be kept secret, and a public key {{code language="none"}}~/.ssh/id_rsa.pub{{/code}}.
 . Go to //Projects// → //Create a new project// and call it "personal-<login>", replacing <login> with your own login name.
 . On the next page, create a repository named "turing" (or select //Add repository// on your project page).
--1. Once you are on the repository page, copy the URL shown in //Clone & push urls//.
++1. On the repository page, go to //Manage collaborators// → //Add collaborators// and add the user msp.
++1. Once you are back on the repository page, copy the URL shown in //Clone & push urls//.
 . Email the copied URL to [[msp@informatik.uni-kiel.de>>mailto:msp@informatik.uni-kiel.de||shape="rect"]]. This will serve as proof for your work on this tutorial.
 . (((
  Transfer your {{code language="none"}}master{{/code}} branch to the new server-side repository. Replace the URL in the following command by the one copied from Gitorious:
@@ -373,7 +373,7 @@
  $ cd turing2
  {{/noformat}}
--The {{code language="none"}}clone{{/code}} command automatically creates a remote named {{code language="none"}}origin{{/code}} in the new local repository, which is set to the given URL.
++The {{code language="none"}}clone{{/code}} command automatically creates a remote named {{code language="none"}}origin{{/code}} in the new local repository, which is set to the given URL. You will use this second clone to simulate another user with access to the repository.
  )))
 . Edit the file {{code language="none"}}examples.txt{{/code}} in the new clone ({{code language="none"}}turing2{{/code}}): replace {{code language="none"}}"a"{{/code}} in line 6 by {{code language="none"}}"c"{{/code}} and correct the tape representations in lines 9, 14, and 19 accordingly. Commit the change.
 . (((
@@ -540,10 +540,10 @@
 f686..b58ded7  master -> master
  {{/noformat}}
--While {{code language="none"}}pull{{/code}} performs a {{code language="none"}}fetch{{/code}} and a {{code language="none"}}merge{{/code}}, {{code language="none"}}push{{/code}} transfers the new merged branch to the server. Note that during the merge operation conflicts can occur. In that case you have to resolve them and commit the changes before you can push.
++While {{code language="none"}}pull{{/code}} performs a {{code language="none"}}fetch{{/code}} and a {{code language="none"}}merge{{/code}}, {{code language="none"}}push{{/code}} transfers the new merged branch to the server. Note that during the merge operation conflicts can occur. In that case you have to resolve them and commit the changes before you can push. When used without parameters like shown above, {{code language="none"}}pull{{/code}} lookes in {{code language="none"}}.git/config{{/code}} to determine which branches to pull from which remotes.
  )))
 . (((
--In order to check out the {{code language="none"}}sketches{{/code}} branch, which was previously pushed to the server, simply type the following command:
++In order to check out the {{code language="none"}}sketches{{/code}} branch locally, which was previously pushed to the server, simply type the following command:
  {{noformat}}
  $ git checkout sketches
@@ -551,7 +551,7 @@
  Switched to a new branch 'sketches'
  {{/noformat}}
--This branch can be pushed and pulled with the server in the same way as you did for the {{code language="none"}}master{{/code}} branch.
++This branch can be pushed and pulled with the server in the same way as you did for the {{code language="none"}}master{{/code}} branch. Never check out {{code language="none"}}origin/sketches{{/code}}, since that is a remote tracking branch!
  )))
  The {{code language="none"}}master{{/code}} branch should look like this:
@@ -558,4 +558,116 @@
  [[image:attach:turing-graph-02.png]]
--
++= Other Useful Commands =
++
++This section contains optional steps that you don't need to push online, but can be useful for you to learn.
++
++=== Ignoring Files ===
++
++While working on his Machine, Alan Turing has produced a temporary file {{code language="none"}}experiments.tmp{{/code}}, which he does not want to commit in the repository:
++
++{{noformat}}
++$ git status
++# On branch master
++# Untracked files:
++#   (use "git add <file>..." to include in what will be committed)
++#
++#       experiments.tmp
++nothing added to commit but untracked files present (use "git add" to track)
++{{/noformat}}
++
++Since the extra mention of that file can make Git's status reports unnecessarily cluttered, Alan wants to ignore it permanently. Help him by adding a {{code language="none"}}.gitignore{{/code}} file to the repository:
++
++{{noformat}}
++$ echo "*.tmp" > .gitignore
++$ git add .gitignore
++$ git commit -m "added ignore file"
++[master 738ce4c] added ignore file
++ 1 files changed, 1 insertions(+), 0 deletions(-)
++ create mode 100644 .gitignore
++$ git status
++# On branch master
++# Your branch is ahead of 'origin/master' by 1 commit.
++#
++nothing to commit (working directory clean)
++{{/noformat}}
++
++Now the experiments.tmp{{code language="none"}}{{/code}} file is not considered when viewing the status. You can add arbitrary file name patterns to the {{code language="none"}}.gitignore{{/code}} file; for example it is a good idea to ignore {{code language="none"}}*.class{{/code}}, which are binary files generated for Java projects.
++
++=== Discarding Changes ===
++
++While working on his Machine, Alan Turing has made some changes to notes.txt that he later found out to be nonsense:
++
++{{noformat}}
++$ git status
++# On branch master
++# Changed but not updated:
++#   (use "git add <file>..." to update what will be committed)
++#   (use "git checkout -- <file>..." to discard changes in working directory)
++#
++#       modified:   notes.txt
++#
++no changes added to commit (use "git add" and/or "git commit -a")
++{{/noformat}}
++
++Help Alan by restoring the last committed state of that file:
++
++{{noformat}}
++$ git checkout HEAD notes.txt
++$ git status
++# On branch master
++nothing to commit (working directory clean)
++{{/noformat}}
++
++Instead of HEAD, which is the last commit on the current branch, you can also name any other branch or commit hash. In that case you would have to commit the change to make it permanent. While resolving conflicts it is possible to use {{code language="none"}}--theirs{{/code}} or {{code language="none"}}--ours{{/code}} instead of HEAD, which replaces the whole content of the respective file by their version (the one on the remote branch) or our version (the one on the current branch).
++
++A more brute-force option is using the {{code language="none"}}reset{{/code}} command:
++
++{{noformat}}
++$ git reset --hard
++HEAD is now at b58ded7 Merge branch 'master' of git.rtsys.informatik.uni-kiel.de:personal-msp/turing
++{{/noformat}}
++
++This resets //all// changes to the working copy to the head of the current branch, so use it with caution! However, {{code language="none"}}reset{{/code}} does not remove unstaged files. In order to do that in one command, use {{code language="none"}}clean{{/code}}:
++
++{{noformat}}
++$ git status
++# On branch master
++# Untracked files:
++#   (use "git add <file>..." to include in what will be committed)
++#
++#       test1.tmp
++#       test2.tmp
++nothing added to commit but untracked files present (use "git add" to track)
++$ git clean -f
++Removing test1.tmp
++Removing test2.tmp
++{{/noformat}}
++
++=== Rebasing ===
++
++Consider the following situation:
++
++[[image:attach:turing-graph-03.png]]
++
++If you want to merge the changes made on the {{code language="none"}}master{{/code}} branch into the {{code language="none"}}sketches{{/code}} branch, the normal way is to use the {{code language="none"}}merge{{/code}} command and create a merge commit. However, the {{code language="none"}}rebase{{/code}} command gives an interesting alternative to that: it reapplies all commits done in the current branch starting from a given reference.
++
++{{noformat}}
++$ git rebase master
++First, rewinding head to replay your work on top of it...
++Applying: added another example
++Applying: state transitions
++Using index info to reconstruct a base tree...
++Falling back to patching base and 3-way merge...
++Auto-merging notes.txt
++{{/noformat}}
++
++Afterwards the commit graph looks like this:
++
++[[image:attach:turing-graph-04.png]]
++
++The two commits made in {{code language="none"}}sketches{{/code}} are reapplied starting from the head of the {{code language="none"}}master{{/code}} branch. The resulting structure of commits is much cleaner than before. It is even possible to squeeze multiple commits into one using {{code language="none"}}rebase{{/code}}. Note that in this example a merge conflict had to be resolved in the same way as it was done in Section "Branching and Merging"; instead of committing the resolved file, the rebase command is resumed with {{code language="none"}}git rebase --continue{{/code}}.
++
++{{warning}}
++Never rebase a branch that is already pushed online! Due to the structural change the rebased branch is no longer compatible with the previous one, and pushing it will fail, since fast-forward merge is not possible.
++{{/warning}}

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@@ -1,1 +1,1 @@
--2982155
++2982168

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@@ -1,1 +1,1 @@
--https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/WS12EclPract/pages/2982155/Git
++https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/WS12EclPract/pages/2982168/Git

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