1Git for CVS users 2================= 3 4Ok, so you're a CVS user. That's ok, it's a treatable condition, and the 5first step to recovery is admitting you have a problem. The fact that 6you are reading this file means that you may be well on that path 7already. 8 9The thing about CVS is that it absolutely sucks as a source control 10manager, and you'll thus be happy with almost anything else. Git, 11however, may be a bit _too_ different (read: "good") for your taste, and 12does a lot of things differently. 13 14One particular suckage of CVS is very hard to work around: CVS is 15basically a tool for tracking _file_ history, while git is a tool for 16tracking _project_ history. This sometimes causes problems if you are 17used to doing very strange things in CVS, in particular if you're doing 18things like making branches of just a subset of the project. Git can't 19track that, since git never tracks things on the level of an individual 20file, only on the whole project level. 21 22The good news is that most people don't do that, and in fact most sane 23people think it's a bug in CVS that makes it tag (and check in changes) 24one file at a time. So most projects you'll ever see will use CVS 25_as_if_ it was sane. In which case you'll find it very easy indeed to 26move over to Git. 27 28First off: this is not a git tutorial. See Documentation/tutorial.txt 29for how git actually works. This is more of a random collection of 30gotcha's and notes on converting from CVS to git. 31 32Second: CVS has the notion of a "repository" as opposed to the thing 33that you're actually working in (your working directory, or your 34"checked out tree"). Git does not have that notion at all, and all git 35working directories _are_ the repositories. However, you can easily 36emulate the CVS model by having one special "global repository", which 37people can synchronize with. See details later, but in the meantime 38just keep in mind that with git, every checked out working tree will 39have a full revision control history of its own. 40 41 42Importing a CVS archive 43----------------------- 44 45Ok, you have an old project, and you want to at least give git a chance 46to see how it performs. The first thing you want to do (after you've 47gone through the git tutorial, and generally familiarized yourself with 48how to commit stuff etc in git) is to create a git'ified version of your 49CVS archive. 50 51Happily, that's very easy indeed. Git will do it for you, although git 52will need the help of a program called "cvsps": 53 54 http://www.cobite.com/cvsps/ 55 56which is not actually related to git at all, but which makes CVS usage 57look almost sane (ie you almost certainly want to have it even if you 58decide to stay with CVS). However, git will want at _least_ version 2.1 59of cvsps (available at the address above), and in fact will currently 60refuse to work with anything else. 61 62Once you've gotten (and installed) cvsps, you may or may not want to get 63any more familiar with it, but make sure it is in your path. After that, 64the magic command line is 65 66 git cvsimport <cvsroot> <module> 67 68which will do exactly what you'd think it does: it will create a git 69archive of the named CVS module. The new archive will be created in a 70subdirectory named <module>. 71 72It can take some time to actually do the conversion for a large archive 73since it involves checking out from CVS every revision of every file, 74and the conversion script can be reasonably chatty, but on some not very 75scientific tests it averaged about eight revisions per second, so a 76medium-sized project should not take more than a couple of minutes. For 77larger projects or remote repositories, the process may take longer. 78 79 80Emulating CVS behaviour 81----------------------- 82 83 84FIXME! Talk about setting up several repositories, and pulling and 85pushing between them. Talk about merging, and branches. Some of this 86needs to be in the tutorial too. 87 88 89 90CVS annotate 91------------ 92 93So, something has gone wrong, and you don't know whom to blame, and 94you're an ex-CVS user and used to do "cvs annotate" to see who caused 95the breakage. You're looking for the "git annotate", and it's just 96claiming not to find such a script. You're annoyed. 97 98Yes, that's right. Core git doesn't do "annotate", although it's 99technically possible, and there are at least two specialized scripts out 100there that can be used to get equivalent information (see the git 101mailing list archives for details). 102 103Git has a couple of alternatives, though, that you may find sufficient 104or even superior depending on your use. One is called "git-whatchanged" 105(for obvious reasons) and the other one is called "pickaxe" ("a tool for 106the software archeologist"). 107 108The "git-whatchanged" script is a truly trivial script that can give you 109a good overview of what has changed in a file or a directory (or an 110arbitrary list of files or directories). The "pickaxe" support is an 111additional layer that can be used to further specify exactly what you're 112looking for, if you already know the specific area that changed. 113 114Let's step back a bit and think about the reason why you would 115want to do "cvs annotate a-file.c" to begin with. 116 117You would use "cvs annotate" on a file when you have trouble 118with a function (or even a single "if" statement in a function) 119that happens to be defined in the file, which does not do what 120you want it to do. And you would want to find out why it was 121written that way, because you are about to modify it to suit 122your needs, and at the same time you do not want to break its 123current callers. For that, you are trying to find out why the 124original author did things that way in the original context. 125 126Many times, it may be enough to see the commit log messages of 127commits that touch the file in question, possibly along with the 128patches themselves, like this: 129 130 $ git-whatchanged -p a-file.c 131 132This will show log messages and patches for each commit that 133touches a-file. 134 135This, however, may not be very useful when this file has many 136modifications that are not related to the piece of code you are 137interested in. You would see many log messages and patches that 138do not have anything to do with the piece of code you are 139interested in. As an example, assuming that you have this piece 140code that you are interested in in the HEAD version: 141 142 if (frotz) { 143 nitfol(); 144 } 145 146you would use git-rev-list and git-diff-tree like this: 147 148 $ git-rev-list HEAD | 149 git-diff-tree --stdin -v -p -S'if (frotz) { 150 nitfol(); 151 }' 152 153We have already talked about the "--stdin" form of git-diff-tree 154command that reads the list of commits and compares each commit 155with its parents. The git-whatchanged command internally runs 156the equivalent of the above command, and can be used like this: 157 158 $ git-whatchanged -p -S'if (frotz) { 159 nitfol(); 160 }' 161 162When the -S option is used, git-diff-tree command outputs 163differences between two commits only if one tree has the 164specified string in a file and the corresponding file in the 165other tree does not. The above example looks for a commit that 166has the "if" statement in it in a file, but its parent commit 167does not have it in the same shape in the corresponding file (or 168the other way around, where the parent has it and the commit 169does not), and the differences between them are shown, along 170with the commit message (thanks to the -v flag). It does not 171show anything for commits that do not touch this "if" statement. 172 173Also, in the original context, the same statement might have 174appeared at first in a different file and later the file was 175renamed to "a-file.c". CVS annotate would not help you to go 176back across such a rename, but GIT would still help you in such 177a situation. For that, you can give the -C flag to 178git-diff-tree, like this: 179 180 $ git-whatchanged -p -C -S'if (frotz) { 181 nitfol(); 182 }' 183 184When the -C flag is used, file renames and copies are followed. 185So if the "if" statement in question happens to be in "a-file.c" 186in the current HEAD commit, even if the file was originally 187called "o-file.c" and then renamed in an earlier commit, or if 188the file was created by copying an existing "o-file.c" in an 189earlier commit, you will not lose track. If the "if" statement 190did not change across such rename or copy, then the commit that 191does rename or copy would not show in the output, and if the 192"if" statement was modified while the file was still called 193"o-file.c", it would find the commit that changed the statement 194when it was in "o-file.c". 195 196[ BTW, the current versions of "git-diff-tree -C" is not eager 197 enough to find copies, and it will miss the fact that a-file.c 198 was created by copying o-file.c unless o-file.c was somehow 199 changed in the same commit.] 200 201You can use the --pickaxe-all flag in addition to the -S flag. 202This causes the differences from all the files contained in 203those two commits, not just the differences between the files 204that contain this changed "if" statement: 205 206 $ git-whatchanged -p -C -S'if (frotz) { 207 nitfol(); 208 }' --pickaxe-all 209 210[ Side note. This option is called "--pickaxe-all" because -S 211 option is internally called "pickaxe", a tool for software 212 archaeologists.]