Wiki source code of Git

Last modified by Richard Kreissig on 2023/09/14 09:16
Hide last authors
uru 3.1 1 This tutorial will address the source code management (SCM) tool named [[Git>>url:http://git-scm.com/||shape="rect"]]. By following these steps you should learn about the basic usage of Git. Furthermore, Git is a great SCM tool, and it's good to know how to use it. During this tutorial, we will follow Alan Turing's thoughts towards developing the [[Turing Machine>>url:http://en.wikipedia.org/wiki/Turing_machine||shape="rect"]].
uru 1.1 2
3 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.
4
5 === Contents ===
6
7
8
9 {{toc style="circle" maxLevel="2"/}}
10
11 = Creating Commits =
12
13 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.
14
15 1. 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).
16 1. 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"]].
17 1. (((
18 Configure your name and email address (will be included in all commits you create):
19
Richard Kreissig 5.1 20 {{code}}
uru 1.1 21 $ git config --global --add user.name "Your Name"
22 $ git config --global --add user.email "<login>@informatik.uni-kiel.de"
Richard Kreissig 5.1 23 {{/code}}
uru 1.1 24 )))
25 1. (((
26 Create a local repository for the "//Turing Project//":
27
Richard Kreissig 5.1 28 {{code}}
uru 1.1 29 $ mkdir turing
30 $ cd turing
31 $ git init
32 Initialized empty Git repository in ~/turing/.git/
Richard Kreissig 5.1 33 {{/code}}
uru 1.1 34
35 The {{code language="none"}}.git{{/code}} subdirectory contains all history and metadata of the repository. You should not modify it. The {{code language="none"}}turing{{/code}} directory contains the //working copy//, that is the currently checked-out snapshot. You work by modifying your working copy and committing the modifications to the repository (contained in {{code language="none"}}.git{{/code}}).
36 )))
37 1. (((
38 Add and commit some content: copy [[attach:notes.txt]]{{code language="none"}}{{/code}} to your {{code language="none"}}turing{{/code}} directory.
39
Richard Kreissig 5.1 40 {{code}}
uru 1.1 41 $ git add notes.txt
42 $ git commit -m "wrote some first notes"
43 [master (root-commit) 2e73b34] wrote some first notes
44 1 files changed, 5 insertions(+), 0 deletions(-)
45 create mode 100644 notes.txt
Richard Kreissig 5.1 46 {{/code}}
uru 1.1 47
48 The file is now stored in the local history of your repository.
49 )))
Richard Kreissig 5.1 50 1. Edit {{code language="none"}}notes.txt{{/code}}:
uru 1.1 51 11. Replace "fixed" with "infinite" in line 1.
52 11. Replace "... (TODO)" with "a finite state machine" in line 4.
53 1. (((
54 View the status of your current working copy:
55
Richard Kreissig 5.1 56 {{code}}
uru 1.1 57 $ git status
58 # On branch master
59 # Changed but not updated:
60 # (use "git add <file>..." to update what will be committed)
61 # (use "git checkout -- <file>..." to discard changes in working directory)
62 #
63 # modified: notes.txt
64 #
65 no changes added to commit (use "git add" and/or "git commit -a")
Richard Kreissig 5.1 66 {{/code}}
uru 1.1 67 )))
68 1. (((
69 Mark the modified file to include it in the next commit, then view the status again and compare with the previous output:
70
Richard Kreissig 5.1 71 {{code}}
uru 1.1 72 $ git add notes.txt
73 $ git status
74 # On branch master
75 # Changes to be committed:
76 # (use "git reset HEAD <file>..." to unstage)
77 #
78 # modified: notes.txt
79 #
Richard Kreissig 5.1 80 {{/code}}
uru 1.1 81 )))
82 1. (((
83 Commit the modified content to your local repository and view the status:
84
Richard Kreissig 5.1 85 {{code}}
uru 1.1 86 $ git commit -m "modified tape length, found a controller for tape head"
87 [master 52e2d49] modified tape length, found a controller for tape head
88 1 files changed, 2 insertions(+), 2 deletions(-)
89 $ git status
90 # On branch master
91 nothing to commit (working directory clean)
Richard Kreissig 5.1 92 {{/code}}
uru 1.1 93 )))
94
95 After the preceding steps you have two commits in your local repository, each with one file in the index. You have different commands for viewing these commits:
96
Richard Kreissig 5.1 97 {{code}}
uru 1.1 98 $ git log
99 commit 52e2d4946791c2725015853e5e261ce143c6fe8a
100 Author: Miro Spoenemann <msp@informatik.uni-kiel.de>
101 Date: Mon Oct 15 15:00:14 2012 +0200
102
103 modified tape length, found a controller for tape head
104
105 commit 2e73b34ac44480773fc0e52875b7353a087d8c6d
106 Author: Miro Spoenemann <msp@informatik.uni-kiel.de>
107 Date: Mon Oct 15 12:14:06 2012 +0200
108
109 wrote some first notes
110  
111 $ git show 52e2d49
112 commit 52e2d4946791c2725015853e5e261ce143c6fe8a
113 Author: Miro Spoenemann <msp@informatik.uni-kiel.de>
114 Date: Mon Oct 15 15:00:14 2012 +0200
115
116 modified tape length, found a controller for tape head
117
118 diff --git a/notes.txt b/notes.txt
119 index 4ded2b3..bd422b3 100644
120 --- a/notes.txt
121 +++ b/notes.txt
122 @@ -1,5 +1,5 @@
123 - * A tape with fixed length
124 + * A tape with infinite length
125 * Tape head can read or write data
126 * Tape head can move left or right
127 - * The head is controlled by ... (TODO)
128 + * The head is controlled by a finite state machine
Richard Kreissig 5.1 129 {{/code}}
uru 1.1 130
131 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"]]).
132
133 = Branching and Merging =
134
135 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.
136
137 1. (((
138 Create a branch with name //sketches//:
139
Richard Kreissig 5.1 140 {{code}}
uru 1.1 141 $ git branch sketches
Richard Kreissig 5.1 142 {{/code}}
uru 1.1 143 )))
144 1. (((
145 View the list of branches:
146
Richard Kreissig 5.1 147 {{code}}
uru 1.1 148 $ git branch
149 * master
150 sketches
Richard Kreissig 5.1 151 {{/code}}
uru 1.1 152
153 The star reveals that you are still on the old {{code language="none"}}master{{/code}} branch.
154 )))
155 1. (((
156 Switch to the new branch:
157
Richard Kreissig 5.1 158 {{code}}
uru 1.1 159 $ git checkout sketches
160 Switched to branch 'sketches'
161 $ git branch
162 master
163 * sketches
Richard Kreissig 5.1 164 {{/code}}
uru 1.1 165
166 It is also possible to create a branch and switch immediately to it using the option {{code language="none"}}-b{{/code}} of {{code language="none"}}git checkout{{/code}}.
167 )))
168 1. (((
169 Download and add the new file [[attach:examples.txt]]{{code language="none"}}{{/code}}:
170
Richard Kreissig 5.1 171 {{code}}
uru 1.1 172 $ git add examples.txt
173 $ git commit -m "wrote first examples"
174 [sketches cd63135] wrote first examples
175 1 files changed, 20 insertions(+), 0 deletions(-)
176 create mode 100644 examples.txt
Richard Kreissig 5.1 177 {{/code}}
uru 1.1 178
179 Inspecting the commit graph with {{code language="none"}}gitk{{/code}} (or another graphical viewer) you see that the {{code language="none"}}sketches{{/code}} branch now has three commits, while {{code language="none"}}master{{/code}} is still at the second commit.
180 )))
181 1. (((
182 Merging the {{code language="none"}}sketches{{/code}} branch into {{code language="none"}}master{{/code}} means that all changes that have been made in {{code language="none"}}sketches{{/code}} are also applied to {{code language="none"}}master{{/code}}. In order to perform this merge, we have to check out the {{code language="none"}}master{{/code}} branch first:
183
Richard Kreissig 5.1 184 {{code}}
uru 1.1 185 $ git checkout master
186 Switched to branch 'master'
187 $ git merge sketches
188 Updating 52e2d49..cd63135
189 Fast-forward
190 examples.txt | 20 ++++++++++++++++++++
191 1 files changed, 20 insertions(+), 0 deletions(-)
192 create mode 100644 examples.txt
Richard Kreissig 5.1 193 {{/code}}
uru 1.1 194
195 This was a //fast-forward// merge: since the {{code language="none"}}master{{/code}} branch was completely contained in the {{code language="none"}}sketches{{/code}} branch, the merge could be done by simply changing the head pointer of {{code language="none"}}master{{/code}} to be the same as the head of {{code language="none"}}sketches{{/code}}.
196 )))
197 1. (((
198 Now add the line "{{code language="none"}}see some examples in 'examples.txt'{{/code}}" to the file {{code language="none"}}notes.txt{{/code}} and commit this change in the current branch:
199
Richard Kreissig 5.1 200 {{code}}
uru 1.1 201 $ git add notes.txt
202 $ git commit -m "added reference to the new examples"
203 [master a5e244f] added reference to the new examples
204 1 files changed, 2 insertions(+), 1 deletions(-)
Richard Kreissig 5.1 205 {{/code}}
uru 1.1 206 )))
207 1. (((
208 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.
209
Richard Kreissig 5.1 210 {{code}}
uru 1.1 211 $ git checkout sketches
212 Switched to branch 'sketches'
Richard Kreissig 5.1 213 {{/code}}
uru 1.1 214
215 Add the line "{{code language="none"}}Move one step left:{{/code}}" followed by an accordingly updated version of the tape with tape head at the end of the file {{code language="none"}}examples.txt{{/code}}, then commit.
216
Richard Kreissig 5.1 217 {{code}}
uru 1.1 218 $ git add examples.txt
219 $ git commit -m "added another example"
220 [sketches 55a9cb1] added another example
221 1 files changed, 5 insertions(+), 0 deletions(-)
Richard Kreissig 5.1 222 {{/code}}
uru 1.1 223
224 Now your two branches have //diverged//, which means that they cannot be fast-forwarded anymore.
225 )))
226 1. (((
227 Merge the {{code language="none"}}master{{/code}} branch into {{code language="none"}}sketches{{/code}}:
228
Richard Kreissig 5.1 229 {{code}}
uru 1.1 230 $ git merge master
231 Merge made by recursive.
232 notes.txt | 3 ++-
233 1 files changed, 2 insertions(+), 1 deletions(-)
Richard Kreissig 5.1 234 {{/code}}
uru 1.1 235
236 Using {{code language="none"}}gitk{{/code}} you can see that a new commit was created that has two parent commits. Such a commit is called //merge// commit and is done automatically when a non-fast-forward merge is applied. See how both the change to {{code language="none"}}notes.txt{{/code}} done in the {{code language="none"}}master{{/code}} branch and the change to {{code language="none"}}examples.txt{{/code}} done in the {{code language="none"}}sketches{{/code}} branch are now contained in the repository state that results from the merge.
237 )))
238 1. (((
239 Add a commit in each of the two branches using the commands you have already learned.
Richard Kreissig 5.1 240
uru 1.1 241 1. Check out {{code language="none"}}master{{/code}}.
242 1. (((
243 Insert the following line after line 4 of {{code language="none"}}notes.txt{{/code}}:
244
Richard Kreissig 5.1 245 {{code nopanel="true"}}
uru 1.1 246 * The finite state machine has an initial state and one or more final states
Richard Kreissig 5.1 247 {{/code}}
uru 1.1 248 )))
249 1. Commit the change of {{code language="none"}}notes.txt{{/code}}.
250 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).
251 1. (((
252 Insert the following line after line 4 of {{code language="none"}}notes.txt{{/code}}:
253
Richard Kreissig 5.1 254 {{code nopanel="true"}}
uru 1.1 255 * Each state transition can trigger head movement and data read/write
Richard Kreissig 5.1 256 {{/code}}
uru 1.1 257 )))
258 1. Commit the change of {{code language="none"}}notes.txt{{/code}}.
259 )))
260 1. (((
261 Merge the {{code language="none"}}master{{/code}} branch into the current branch ({{code language="none"}}sketches{{/code}}):
262
Richard Kreissig 5.1 263 {{code}}
uru 1.1 264 $ git merge master
265 Auto-merging notes.txt
266 CONFLICT (content): Merge conflict in notes.txt
267 Automatic merge failed; fix conflicts and then commit the result.
Richard Kreissig 5.1 268 {{/code}}
uru 1.1 269
270 As expected, the branches could not be merged automatically, since both branches modified the same line in the same file.
271 )))
272 1. (((
273 Use the {{code language="none"}}status{{/code}} command to see the list of affected files:
274
Richard Kreissig 5.1 275 {{code}}
uru 1.1 276 $ git status
277 # On branch sketches
278 # Unmerged paths:
279 # (use "git add/rm <file>..." as appropriate to mark resolution)
280 #
281 # both modified: notes.txt
282 #
283 no changes added to commit (use "git add" and/or "git commit -a")
Richard Kreissig 5.1 284 {{/code}}
uru 1.1 285 )))
286 1. (((
287 The modified {{code language="none"}}notes.txt{{/code}} should now contain the following text:
288
Richard Kreissig 5.1 289 {{code nopanel="true"}}
uru 1.1 290 <<<<<<< HEAD
291 * Each state transition can trigger head movement and data read/write
292 =======
293 * The finite state machine has an initial state and one or more final states
294 >>>>>>> master
Richard Kreissig 5.1 295 {{/code}}
uru 1.1 296
297 The upper line is the one committed to {{code language="none"}}sketches{{/code}}, while the lower line was committed to {{code language="none"}}master{{/code}}. You have to resolve the conflict by editing the file. In this case the conflict is resolved by keeping both lines in arbitrary order, that means you should just remove the conflict markers (lines 5, 7, and 9 in {{code language="none"}}notes.txt{{/code}}).
298 )))
299 1. (((
300 Use the {{code language="none"}}add{{/code}} command to mark {{code language="none"}}notes.txt{{/code}} as resolved. Entering {{code language="none"}}git commit{{/code}} without a message will open a text editor with an automatically created commit message. Just close the editor, and the merge commit is completed:
301
Richard Kreissig 5.1 302 {{code}}
uru 1.1 303 $ git commit
304 [sketches 21d5ddb] Merge branch 'master' into sketches
305 $ git show 21d5ddb
306 commit 21d5ddbbcba4e36464653a2a550dbf595ead921f
307 Merge: 17f75c7 8af2d50
308 Author: Miro Spoenemann <msp@informatik.uni-kiel.de>
309 Date: Tue Oct 16 10:44:09 2012 +0200
310
311 Merge branch 'master' into sketches
312
313 Conflicts:
314 notes.txt
315
316 diff --cc notes.txt
317 index 8f72873,bb81298..ba94a08
318 --- a/notes.txt
319 +++ b/notes.txt
320 @@@ -2,6 -2,6 +2,7 @@@
321 * Tape head can read or write data
322 * Tape head can move left or right
323 * The head is controlled by a finite state machine
324 + * Each state transition can trigger head movement and data read/write
325 + * The finite state machine has an initial state and one or more final states
326 see some examples in 'examples.txt'
Richard Kreissig 5.1 327 {{/code}}
uru 1.1 328 )))
329
330 The {{code language="none"}}gitk{{/code}} tool should now display this graph:
331
332 [[image:attach:turing-graph-01.png]]
333
334 = Remote Repositories =
335
Richard Kreissig 5.1 336 In the previous sections you have worked only with a local repository. The next step is to share this content with a remote repository, which we manage with [[Stash>>url:https://www.atlassian.com/software/stash/overview||shape="rect"]]. (% style="font-size:10.0pt; line-height:13.0pt" %)You will first have to configure your Stash account:
uru 1.1 337
338 1. Login to [[our Stash server>>url:http://git.rtsys.informatik.uni-kiel.de/||shape="rect"]] with your Rtsys account information. If you haven't received your password yet, either wait until you have that password or register yourself in Stash (but don't use your IfI login name – that one will be used later when we create your account).
339 1. Through the button in the top right corner, access your profile.
340 1. Switch to the //SSH keys// tab.
Richard Kreissig 5.1 341 1. Click //Add Key// and upload a public SSH key that you want to use to access the repository.
342 1*. (% style="font-size:10.0pt; line-height:13.0pt" %)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}}.
uru 1.1 343
344 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.
345
Richard Kreissig 5.1 346 1. (% style="font-size:10.0pt; line-height:13.0pt" %)Go to [[Stash>>url:http://git.rtsys.informatik.uni-kiel.de/||shape="rect"]] → //Create Project// and call it "personal-<login>", replacing <login> with your own login name. Use your uppercase login name as project key, e.g. "MSP".
uru 1.1 347 1. Go to the //Permissions// tab of the project page and add the user "msp" as observer.
348 1. On the project page, select //Create Repository// and name it "turing".
Richard Kreissig 5.1 349 1. (% style="font-size:10.0pt; line-height:13.0pt" %)Copy the SSH URL shown in the top right and email it to (%%)[[msp@informatik.uni-kiel.de>>mailto:msp@informatik.uni-kiel.de||shape="rect" style="font-size: 10.0pt;line-height: 13.0pt;"]](% style="font-size:10.0pt; line-height:13.0pt" %). This will serve as proof for your work on this tutorial.
uru 1.1 350 1. (((
351 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 Stash:
352
Richard Kreissig 5.1 353 {{code}}
uru 1.1 354 $ git remote add stash ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
355 $ git push stash master
356 Counting objects: 15, done.
357 Delta compression using up to 16 threads.
358 Compressing objects: 100% (13/13), done.
359 Writing objects: 100% (15/15), 1.54 KiB, done.
360 Total 15 (delta 3), reused 0 (delta 0)
361 To ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
362 * [new branch] master -> master
Richard Kreissig 5.1 363 {{/code}}
uru 1.1 364
365 The first command adds a //remote// named "stash" to your local repository, which is just a bookmark for the long URL. The second command transfers the {{code language="none"}}master{{/code}} branch to the server, which is called //pushing//. After that is done, reload the Stash page in your browser, and you see all changes that are transferred to the server-side repository.
366 )))
367 1. (((
368 Create a local clone of your remote repository (replace the URL accordingly):
369
Richard Kreissig 5.1 370 {{code}}
uru 1.1 371 $ cd ..
372 $ git clone ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git turing2
373 Initialized empty Git repository in /home/msp/tmp/turing2/.git/
374 remote: Counting objects: 15, done.
375 remote: Compressing objects: 100% (13/13), done.
376 remote: Total 15 (delta 3), reused 0 (delta 0)
377 Receiving objects: 100% (15/15), done.
378 Resolving deltas: 100% (3/3), done.
379 $ cd turing2
Richard Kreissig 5.1 380 {{/code}}
uru 1.1 381
382 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.
383 )))
384 1. 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.
385 1. (((
386 Push the new commit to the server:
387
Richard Kreissig 5.1 388 {{code}}
uru 1.1 389 $ git push
390 Counting objects: 5, done.
391 Delta compression using up to 16 threads.
392 Compressing objects: 100% (3/3), done.
393 Writing objects: 100% (3/3), 362 bytes, done.
394 Total 3 (delta 1), reused 0 (delta 0)
395 To ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
396 8af2d50..1d1577f master -> master
Richard Kreissig 5.1 397 {{/code}}
uru 1.1 398
399 In this case the push command can be used without arguments, which means that it pushes all branches as configured in {{code language="none"}}.git/config{{/code}}:
400
Richard Kreissig 5.1 401 {{code}}
uru 1.1 402 $ more .git/config
403 [core]
404 repositoryformatversion = 0
405 filemode = true
406 bare = false
407 logallrefupdates = true
408 [remote "origin"]
409 fetch = +refs/heads/*:refs/remotes/origin/*
410 url = ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
411 [branch "master"]
412 remote = origin
413 merge = refs/heads/master
Richard Kreissig 5.1 414 {{/code}}
uru 1.1 415
416 Here the branch {{code language="none"}}master{{/code}} is linked with the remote {{code language="none"}}origin{{/code}}, hence {{code language="none"}}git push{{/code}} does the same as {{code language="none"}}git push origin master{{/code}}.
417 )))
418 1. (((
419 Go back to the original local repository and check out the {{code language="none"}}master{{/code}} branch:
420
Richard Kreissig 5.1 421 {{code}}
uru 1.1 422 $ cd ../turing
423 $ git checkout master
424 Switched to branch 'master'
Richard Kreissig 5.1 425 {{/code}}
uru 1.1 426 )))
427 1. (((
428 Merge the {{code language="none"}}sketches{{/code}} branch into {{code language="none"}}master{{/code}}:
429
Richard Kreissig 5.1 430 {{code}}
uru 1.1 431 $ git merge sketches
432 Updating 8af2d50..21d5ddb
433 Fast-forward
434 examples.txt | 5 +++++
435 notes.txt | 1 +
436 2 files changed, 6 insertions(+), 0 deletions(-)
Richard Kreissig 5.1 437 {{/code}}
uru 1.1 438
439 Now your local {{code language="none"}}master{{/code}} branch and the one on the server-side repository have diverged
440 )))
441 1. (((
442 Fetch the server-side changes:
443
Richard Kreissig 5.1 444 {{code}}
uru 1.1 445 $ git fetch stash
446 remote: Counting objects: 5, done.
447 remote: Compressing objects: 100% (3/3), done.
448 remote: Total 3 (delta 1), reused 0 (delta 0)
449 Unpacking objects: 100% (3/3), done.
450 From ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
451 8af2d50..1d1577f master -> stash/master
Richard Kreissig 5.1 452 {{/code}}
uru 1.1 453
454 Now the change to {{code language="none"}}examples.txt{{/code}} that was previously committed in the {{code language="none"}}turing2{{/code}} repository is stored in a //remote tracking branch// named {{code language="none"}}stash/master{{/code}}:
455
Richard Kreissig 5.1 456 {{code}}
uru 1.1 457 $ git branch -a
458 * master
459 sketches
460 remotes/stash/master
Richard Kreissig 5.1 461 {{/code}}
uru 1.1 462
463 You can analyze the remote tracking branch using the {{code language="none"}}log{{/code}} and {{code language="none"}}show{{/code}} commands. However, you should never directly modify a remote tracking branch.
464 )))
465 1. (((
466 You can merge the remote changes into your local {{code language="none"}}master{{/code}} branch with the following command:
467
Richard Kreissig 5.1 468 {{code}}
uru 1.1 469 $ git merge stash/master
470 Auto-merging examples.txt
471 Merge made by recursive.
472 examples.txt | 8 ++++----
473 1 files changed, 4 insertions(+), 4 deletions(-)
Richard Kreissig 5.1 474 {{/code}}
uru 1.1 475
476 Since this combination of {{code language="none"}}fetch{{/code}} and {{code language="none"}}merge{{/code}} is used very often, Git offers a shortcut for it, namely the {{code language="none"}}pull{{/code}} command. In this case the according command would have been {{code language="none"}}git pull stash master{{/code}}.
477 )))
478 1. (((
479 Push the merged branch to the server, and then push the {{code language="none"}}sketches{{/code}} branch, which is not on the server yet:
480
Richard Kreissig 5.1 481 {{code}}
uru 1.1 482 $ git push stash master
483 Counting objects: 23, done.
484 Delta compression using up to 16 threads.
485 Compressing objects: 100% (14/14), done.
486 Writing objects: 100% (14/14), 1.65 KiB, done.
487 Total 14 (delta 4), reused 0 (delta 0)
488 To ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
489 1d1577f..957f686 master -> master
490 $ git push stash sketches
491 Total 0 (delta 0), reused 0 (delta 0)
492 To ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
493 * [new branch] sketches -> sketches
Richard Kreissig 5.1 494 {{/code}}
uru 1.1 495 )))
496 1. (((
497 As next step change your working directory to the second local repository {{code language="none"}}turing2{{/code}}, add the following line to the end of {{code language="none"}}notes.txt{{/code}} in the {{code language="none"}}turing2{{/code}} directory, and commit the change:
498
Richard Kreissig 5.1 499 {{code nopanel="true"}}
uru 1.1 500 TODO: formal definition
Richard Kreissig 5.1 501 {{/code}}
uru 1.1 502 )))
503 1. (((
504 Trying to push this commit to the server results in the following error message:
505
Richard Kreissig 5.1 506 {{code}}
uru 1.1 507 $ git push
508 To ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
509 ! [rejected] master -> master (non-fast-forward)
510 error: failed to push some refs to 'ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git'
511 To prevent you from losing history, non-fast-forward updates were rejected
512 Merge the remote changes before pushing again. See the 'Note about
513 fast-forwards' section of 'git push --help' for details.
Richard Kreissig 5.1 514 {{/code}}
uru 1.1 515
516 This is because you have modified the branch while working in the original {{code language="none"}}turing{{/code}} repository, and these changes have to be merged with the new commit you have just made for {{code language="none"}}notes.txt{{/code}}.
517 )))
518 1. (((
519 The solution is to apply the {{code language="none"}}pull{{/code}} command followed by the {{code language="none"}}push{{/code}} command:
520
Richard Kreissig 5.1 521 {{code}}
uru 1.1 522 $ git pull
523 remote: Counting objects: 23, done.
524 remote: Compressing objects: 100% (14/14), done.
525 remote: Total 14 (delta 4), reused 0 (delta 0)
526 Unpacking objects: 100% (14/14), done.
527 From ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
528 1d1577f..957f686 master -> origin/master
529 * [new branch] sketches -> origin/sketches
530 Auto-merging notes.txt
531 Merge made by recursive.
532 examples.txt | 5 +++++
533 notes.txt | 1 +
534 2 files changed, 6 insertions(+), 0 deletions(-)
535 $ git push
536 Counting objects: 10, done.
537 Delta compression using up to 16 threads.
538 Compressing objects: 100% (6/6), done.
539 Writing objects: 100% (6/6), 673 bytes, done.
540 Total 6 (delta 2), reused 0 (delta 0)
541 To ssh://git@git.rtsys.informatik.uni-kiel.de:7999/MSP/turing.git
542 957f686..b58ded7 master -> master
Richard Kreissig 5.1 543 {{/code}}
uru 1.1 544
545 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.
546 )))
547 1. (((
548 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:
549
Richard Kreissig 5.1 550 {{code}}
uru 1.1 551 $ git checkout sketches
552 Branch sketches set up to track remote branch sketches from origin.
553 Switched to a new branch 'sketches'
Richard Kreissig 5.1 554 {{/code}}
uru 1.1 555
556 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!
557 )))
558
559 The {{code language="none"}}master{{/code}} branch should look like this:
560
561 [[image:attach:turing-graph-02.png]]
562
563 = Other Useful Commands =
564
565 This section contains optional steps that you don't need to push online, but can be useful for you to learn.
566
567 === Ignoring Files ===
568
569 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:
570
Richard Kreissig 5.1 571 {{code}}
uru 1.1 572 $ git status
573 # On branch master
574 # Untracked files:
575 # (use "git add <file>..." to include in what will be committed)
576 #
577 # experiments.tmp
578 nothing added to commit but untracked files present (use "git add" to track)
Richard Kreissig 5.1 579 {{/code}}
uru 1.1 580
581 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:
582
Richard Kreissig 5.1 583 {{code}}
uru 1.1 584 $ echo "*.tmp" > .gitignore
585 $ git add .gitignore
586 $ git commit -m "added ignore file"
587 [master 738ce4c] added ignore file
588 1 files changed, 1 insertions(+), 0 deletions(-)
589 create mode 100644 .gitignore
590 $ git status
591 # On branch master
592 # Your branch is ahead of 'origin/master' by 1 commit.
593 #
594 nothing to commit (working directory clean)
Richard Kreissig 5.1 595 {{/code}}
uru 1.1 596
597 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.
598
599 === Discarding Changes ===
600
601 While working on his Machine, Alan Turing has made some changes to notes.txt that he later found out to be nonsense:
602
Richard Kreissig 5.1 603 {{code}}
uru 1.1 604 $ git status
605 # On branch master
606 # Changed but not updated:
607 # (use "git add <file>..." to update what will be committed)
608 # (use "git checkout -- <file>..." to discard changes in working directory)
609 #
610 # modified: notes.txt
611 #
612 no changes added to commit (use "git add" and/or "git commit -a")
Richard Kreissig 5.1 613 {{/code}}
uru 1.1 614
615 Help Alan by restoring the last committed state of that file:
616
Richard Kreissig 5.1 617 {{code}}
uru 1.1 618 $ git checkout HEAD notes.txt
619 $ git status
620 # On branch master
621 nothing to commit (working directory clean)
Richard Kreissig 5.1 622 {{/code}}
uru 1.1 623
624 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).
625
626 A more brute-force option is using the {{code language="none"}}reset{{/code}} command:
627
Richard Kreissig 5.1 628 {{code}}
uru 1.1 629 $ git reset --hard
630 HEAD is now at b58ded7 Merge branch 'master' of git.rtsys.informatik.uni-kiel.de:7999/MSP/turing
Richard Kreissig 5.1 631 {{/code}}
uru 1.1 632
633 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}}:
634
Richard Kreissig 5.1 635 {{code}}
uru 1.1 636 $ git status
637 # On branch master
638 # Untracked files:
639 # (use "git add <file>..." to include in what will be committed)
640 #
641 # test1.tmp
642 # test2.tmp
643 nothing added to commit but untracked files present (use "git add" to track)
644 $ git clean -f
645 Removing test1.tmp
646 Removing test2.tmp
Richard Kreissig 5.1 647 {{/code}}
uru 1.1 648
649 === Rebasing ===
650
651 Consider the following situation:
652
653 [[image:attach:turing-graph-03.png]]
654
655 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.
656
Richard Kreissig 5.1 657 {{code}}
uru 1.1 658 $ git rebase master
659 First, rewinding head to replay your work on top of it...
660 Applying: added another example
661 Applying: state transitions
662 Using index info to reconstruct a base tree...
663 Falling back to patching base and 3-way merge...
664 Auto-merging notes.txt
Richard Kreissig 5.1 665 {{/code}}
uru 1.1 666
667 Afterwards the commit graph looks like this:
668
669 [[image:attach:turing-graph-04.png]]
670
671 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. rebase{{code language="none"}}{{/code}} even allows to squeeze multiple commits into one. 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}}.
672
673 {{warning}}
674 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.
675 {{/warning}}
676
677 === Tagging ===
678
679 Finally Alan Turing has made a great success in the development of his Machine, and he would like to fix that stage as "Milestone 1". Help him by tagging the current state of the project:
680
Richard Kreissig 5.1 681 {{code}}
uru 1.1 682 $ git tag milestone1
Richard Kreissig 5.1 683 {{/code}}
uru 1.1 684
685 Then the head of the current branch is stored under the name {{code language="none"}}milestone1{{/code}}, so it can be found very easily at later stages of the project:
686
Richard Kreissig 5.1 687 {{code}}
uru 1.1 688 $ git tag
689 milestone1
690 $ git checkout milestone1
691 Note: checking out 'milestone1'.
692
693 You are in 'detached HEAD' state. You can look around, make experimental
694 changes and commit them, and you can discard any commits you make in this
695 state without impacting any branches by performing another checkout.
696
697 If you want to create a new branch to retain commits you create, you may
698 do so (now or later) by using -b with the checkout command again. Example:
699
700 git checkout -b new_branch_name
701
702 HEAD is now at 957f686... Merge remote branch 'stash/master'
Richard Kreissig 5.1 703 {{/code}}
uru 1.1 704
705 Tags can also be loaded to the server using the {{code language="none"}}push{{/code}} command.

Navigation

Quick Links

KIELER on GitHub
RTSYS Homepage