1A tutorial introduction to git 2============================== 3 4This tutorial explains how to import a new project into git, make 5changes to it, and share changes with other developers. 6 7First, note that you can get documentation for a command such as "git 8diff" with: 9 10------------------------------------------------ 11$ man git-diff 12------------------------------------------------ 13 14It is a good idea to introduce yourself to git before doing any 15operation. The easiest way to do so is: 16 17------------------------------------------------ 18$ cat >~/.gitconfig <<\EOF 19[user] 20 name = Your Name Comes Here 21 email = you@yourdomain.example.com 22EOF 23------------------------------------------------ 24 25 26Importing a new project 27----------------------- 28 29Assume you have a tarball project.tar.gz with your initial work. You 30can place it under git revision control as follows. 31 32------------------------------------------------ 33$ tar xzf project.tar.gz 34$ cd project 35$ git init-db 36------------------------------------------------ 37 38Git will reply 39 40------------------------------------------------ 41defaulting to local storage area 42------------------------------------------------ 43 44You've now initialized the working directory--you may notice a new 45directory created, named ".git". Tell git that you want it to track 46every file under the current directory with (notice the dot '.' 47that means the current directory): 48 49------------------------------------------------ 50$ git add . 51------------------------------------------------ 52 53Finally, 54 55------------------------------------------------ 56$ git commit 57------------------------------------------------ 58 59will prompt you for a commit message, then record the current state 60of all the files to the repository. 61 62Try modifying some files, then run 63 64------------------------------------------------ 65$ git diff 66------------------------------------------------ 67 68to review your changes. When you're done, 69 70------------------------------------------------ 71$ git commit file1 file2... 72------------------------------------------------ 73 74will again prompt your for a message describing the change, and then 75record the new versions of the files you listed. It is cumbersome 76to list all files and you can say `-a` (which stands for 'all') 77instead. 78 79------------------------------------------------ 80$ git commit -a 81------------------------------------------------ 82 83A note on commit messages: Though not required, it's a good idea to 84begin the commit message with a single short (less than 50 character) 85line summarizing the change, followed by a blank line and then a more 86thorough description. Tools that turn commits into email, for 87example, use the first line on the Subject line and the rest of the 88commit in the body. 89 90To add a new file, first create the file, then 91 92------------------------------------------------ 93$ git add path/to/new/file 94------------------------------------------------ 95 96then commit as usual. No special command is required when removing a 97file; just remove it, then tell `commit` about the file as usual. 98 99At any point you can view the history of your changes using 100 101------------------------------------------------ 102$ git log 103------------------------------------------------ 104 105If you also want to see complete diffs at each step, use 106 107------------------------------------------------ 108$ git log -p 109------------------------------------------------ 110 111Managing branches 112----------------- 113 114A single git repository can maintain multiple branches of 115development. To create a new branch named "experimental", use 116 117------------------------------------------------ 118$ git branch experimental 119------------------------------------------------ 120 121If you now run 122 123------------------------------------------------ 124$ git branch 125------------------------------------------------ 126 127you'll get a list of all existing branches: 128 129------------------------------------------------ 130 experimental 131* master 132------------------------------------------------ 133 134The "experimental" branch is the one you just created, and the 135"master" branch is a default branch that was created for you 136automatically. The asterisk marks the branch you are currently on; 137type 138 139------------------------------------------------ 140$ git checkout experimental 141------------------------------------------------ 142 143to switch to the experimental branch. Now edit a file, commit the 144change, and switch back to the master branch: 145 146------------------------------------------------ 147(edit file) 148$ git commit -a 149$ git checkout master 150------------------------------------------------ 151 152Check that the change you made is no longer visible, since it was 153made on the experimental branch and you're back on the master branch. 154 155You can make a different change on the master branch: 156 157------------------------------------------------ 158(edit file) 159$ git commit -a 160------------------------------------------------ 161 162at this point the two branches have diverged, with different changes 163made in each. To merge the changes made in experimental into master, run 164 165------------------------------------------------ 166$ git pull . experimental 167------------------------------------------------ 168 169If the changes don't conflict, you're done. If there are conflicts, 170markers will be left in the problematic files showing the conflict; 171 172------------------------------------------------ 173$ git diff 174------------------------------------------------ 175 176will show this. Once you've edited the files to resolve the 177conflicts, 178 179------------------------------------------------ 180$ git commit -a 181------------------------------------------------ 182 183will commit the result of the merge. Finally, 184 185------------------------------------------------ 186$ gitk 187------------------------------------------------ 188 189will show a nice graphical representation of the resulting history. 190 191If you develop on a branch crazy-idea, then regret it, you can always 192delete the branch with 193 194------------------------------------- 195$ git branch -D crazy-idea 196------------------------------------- 197 198Branches are cheap and easy, so this is a good way to try something 199out. 200 201Using git for collaboration 202--------------------------- 203 204Suppose that Alice has started a new project with a git repository in 205/home/alice/project, and that Bob, who has a home directory on the 206same machine, wants to contribute. 207 208Bob begins with: 209 210------------------------------------------------ 211$ git clone /home/alice/project myrepo 212------------------------------------------------ 213 214This creates a new directory "myrepo" containing a clone of Alice's 215repository. The clone is on an equal footing with the original 216project, possessing its own copy of the original project's history. 217 218Bob then makes some changes and commits them: 219 220------------------------------------------------ 221(edit files) 222$ git commit -a 223(repeat as necessary) 224------------------------------------------------ 225 226When he's ready, he tells Alice to pull changes from the repository 227at /home/bob/myrepo. She does this with: 228 229------------------------------------------------ 230$ cd /home/alice/project 231$ git pull /home/bob/myrepo 232------------------------------------------------ 233 234This actually pulls changes from the branch in Bob's repository named 235"master". Alice could request a different branch by adding the name 236of the branch to the end of the git pull command line. 237 238This merges Bob's changes into her repository; "git log" will 239now show the new commits. If Alice has made her own changes in the 240meantime, then Bob's changes will be merged in, and she will need to 241manually fix any conflicts. 242 243A more cautious Alice might wish to examine Bob's changes before 244pulling them. She can do this by creating a temporary branch just 245for the purpose of studying Bob's changes: 246 247------------------------------------- 248$ git fetch /home/bob/myrepo master:bob-incoming 249------------------------------------- 250 251which fetches the changes from Bob's master branch into a new branch 252named bob-incoming. (Unlike git pull, git fetch just fetches a copy 253of Bob's line of development without doing any merging). Then 254 255------------------------------------- 256$ git log -p master..bob-incoming 257------------------------------------- 258 259shows a list of all the changes that Bob made since he branched from 260Alice's master branch. 261 262After examining those changes, and possibly fixing things, Alice can 263pull the changes into her master branch: 264 265------------------------------------- 266$ git checkout master 267$ git pull . bob-incoming 268------------------------------------- 269 270The last command is a pull from the "bob-incoming" branch in Alice's 271own repository. 272 273Later, Bob can update his repo with Alice's latest changes using 274 275------------------------------------- 276$ git pull 277------------------------------------- 278 279Note that he doesn't need to give the path to Alice's repository; 280when Bob cloned Alice's repository, git stored the location of her 281repository in the file .git/remotes/origin, and that location is used 282as the default for pulls. 283 284Bob may also notice a branch in his repository that he didn't create: 285 286------------------------------------- 287$ git branch 288* master 289 origin 290------------------------------------- 291 292The "origin" branch, which was created automatically by "git clone", 293is a pristine copy of Alice's master branch; Bob should never commit 294to it. 295 296If Bob later decides to work from a different host, he can still 297perform clones and pulls using the ssh protocol: 298 299------------------------------------- 300$ git clone alice.org:/home/alice/project myrepo 301------------------------------------- 302 303Alternatively, git has a native protocol, or can use rsync or http; 304see gitlink:git-pull[1] for details. 305 306Git can also be used in a CVS-like mode, with a central repository 307that various users push changes to; see gitlink:git-push[1] and 308link:cvs-migration.html[git for CVS users]. 309 310Exploring history 311----------------- 312 313Git history is represented as a series of interrelated commits. We 314have already seen that the git log command can list those commits. 315Note that first line of each git log entry also gives a name for the 316commit: 317 318------------------------------------- 319$ git log 320commit c82a22c39cbc32576f64f5c6b3f24b99ea8149c7 321Author: Junio C Hamano <junkio@cox.net> 322Date: Tue May 16 17:18:22 2006 -0700 323 324 merge-base: Clarify the comments on post processing. 325------------------------------------- 326 327We can give this name to git show to see the details about this 328commit. 329 330------------------------------------- 331$ git show c82a22c39cbc32576f64f5c6b3f24b99ea8149c7 332------------------------------------- 333 334But there other ways to refer to commits. You can use any initial 335part of the name that is long enough to uniquely identify the commit: 336 337------------------------------------- 338$ git show c82a22c39c # the first few characters of the name are 339 # usually enough 340$ git show HEAD # the tip of the current branch 341$ git show experimental # the tip of the "experimental" branch 342------------------------------------- 343 344Every commit has at least one "parent" commit, which points to the 345previous state of the project: 346 347------------------------------------- 348$ git show HEAD^ # to see the parent of HEAD 349$ git show HEAD^^ # to see the grandparent of HEAD 350$ git show HEAD~4 # to see the great-great grandparent of HEAD 351------------------------------------- 352 353Note that merge commits may have more than one parent: 354 355------------------------------------- 356$ git show HEAD^1 # show the first parent of HEAD (same as HEAD^) 357$ git show HEAD^2 # show the second parent of HEAD 358------------------------------------- 359 360You can also give commits names of your own; after running 361 362------------------------------------- 363$ git-tag v2.5 1b2e1d63ff 364------------------------------------- 365 366you can refer to 1b2e1d63ff by the name "v2.5". If you intend to 367share this name with other people (for example, to identify a release 368version), you should create a "tag" object, and perhaps sign it; see 369gitlink:git-tag[1] for details. 370 371Any git command that needs to know a commit can take any of these 372names. For example: 373 374------------------------------------- 375$ git diff v2.5 HEAD # compare the current HEAD to v2.5 376$ git branch stable v2.5 # start a new branch named "stable" based 377 # at v2.5 378$ git reset --hard HEAD^ # reset your current branch and working 379 # directory to its state at HEAD^ 380------------------------------------- 381 382Be careful with that last command: in addition to losing any changes 383in the working directory, it will also remove all later commits from 384this branch. If this branch is the only branch containing those 385commits, they will be lost. (Also, don't use "git reset" on a 386publicly-visible branch that other developers pull from, as git will 387be confused by history that disappears in this way.) 388 389The git grep command can search for strings in any version of your 390project, so 391 392------------------------------------- 393$ git grep "hello" v2.5 394------------------------------------- 395 396searches for all occurrences of "hello" in v2.5. 397 398If you leave out the commit name, git grep will search any of the 399files it manages in your current directory. So 400 401------------------------------------- 402$ git grep "hello" 403------------------------------------- 404 405is a quick way to search just the files that are tracked by git. 406 407Many git commands also take sets of commits, which can be specified 408in a number of ways. Here are some examples with git log: 409 410------------------------------------- 411$ git log v2.5..v2.6 # commits between v2.5 and v2.6 412$ git log v2.5.. # commits since v2.5 413$ git log --since="2 weeks ago" # commits from the last 2 weeks 414$ git log v2.5.. Makefile # commits since v2.5 which modify 415 # Makefile 416------------------------------------- 417 418You can also give git log a "range" of commits where the first is not 419necessarily an ancestor of the second; for example, if the tips of 420the branches "stable-release" and "master" diverged from a common 421commit some time ago, then 422 423------------------------------------- 424$ git log stable..experimental 425------------------------------------- 426 427will list commits made in the experimental branch but not in the 428stable branch, while 429 430------------------------------------- 431$ git log experimental..stable 432------------------------------------- 433 434will show the list of commits made on the stable branch but not 435the experimental branch. 436 437The "git log" command has a weakness: it must present commits in a 438list. When the history has lines of development that diverged and 439then merged back together, the order in which "git log" presents 440those commits is meaningless. 441 442Most projects with multiple contributors (such as the linux kernel, 443or git itself) have frequent merges, and gitk does a better job of 444visualizing their history. For example, 445 446------------------------------------- 447$ gitk --since="2 weeks ago" drivers/ 448------------------------------------- 449 450allows you to browse any commits from the last 2 weeks of commits 451that modified files under the "drivers" directory. (Note: you can 452adjust gitk's fonts by holding down the control key while pressing 453"-" or "+".) 454 455Finally, most commands that take filenames will optionally allow you 456to precede any filename by a commit, to specify a particular version 457of the file: 458 459------------------------------------- 460$ git diff v2.5:Makefile HEAD:Makefile.in 461------------------------------------- 462 463You can also use "git cat-file -p" to see any such file: 464 465------------------------------------- 466$ git cat-file -p v2.5:Makefile 467------------------------------------- 468 469Next Steps 470---------- 471 472This tutorial should be enough to perform basic distributed revision 473control for your projects. However, to fully understand the depth 474and power of git you need to understand two simple ideas on which it 475is based: 476 477 * The object database is the rather elegant system used to 478 store the history of your project--files, directories, and 479 commits. 480 481 * The index file is a cache of the state of a directory tree, 482 used to create commits, check out working directories, and 483 hold the various trees involved in a merge. 484 485link:tutorial-2.html[Part two of this tutorial] explains the object 486database, the index file, and a few other odds and ends that you'll 487need to make the most of git. 488 489If you don't want to consider with that right away, a few other 490digressions that may be interesting at this point are: 491 492 * gitlink:git-format-patch[1], gitlink:git-am[1]: These convert 493 series of git commits into emailed patches, and vice versa, 494 useful for projects such as the linux kernel which rely heavily 495 on emailed patches. 496 497 * gitlink:git-bisect[1]: When there is a regression in your 498 project, one way to track down the bug is by searching through 499 the history to find the exact commit that's to blame. Git bisect 500 can help you perform a binary search for that commit. It is 501 smart enough to perform a close-to-optimal search even in the 502 case of complex non-linear history with lots of merged branches. 503 504 * link:everyday.html[Everyday GIT with 20 Commands Or So] 505 506 * link:cvs-migration.html[git for CVS users].