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 doign 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 be 39a full revision control 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, 73and the conversion script can be reasonably chatty, but on some not very 74scientific tests it averaged about eight revisions per second, so a 75medium-sized project should not take more than a couple of minutes. 76 77 78Emulating CVS behaviour 79----------------------- 80 81 82FIXME! Talk about setting up several repositories, and pulling and 83pushing between them. Talk about merging, and branches. Some of this 84needs to be in the tutorial too. 85 86 87 88CVS annotate 89------------ 90 91So, something has gone wrong, and you don't know whom to blame, and 92you're an ex-CVS user and used to do "cvs annotate" to see who caused 93the breakage. You're looking for the "git annotate", and it's just 94claiming not to find such a script. You're annoyed. 95 96Yes, that's right. Core git doesn't do "annotate", although it's 97technically possible, and there are at least two specialized scripts out 98there that can be used to get equivalent information (see the git 99mailing list archives for details). 100 101Git has a couple of alternatives, though, that you may find sufficient 102or even superior depending on your use. One is called "git-whatchanged" 103(for obvious reasons) and the other one is called "pickaxe" ("a tool for 104the software archeologist"). 105 106The "git-whatchanged" script is a truly trivial script that can give you 107a good overview of what has changed in a file or a directory (or an 108arbitrary list of files or directories). The "pickaxe" support is an 109additional layer that can be used to further specify exactly what you're 110looking for, if you already know the specific area that changed. 111 112Let's step back a bit and think about the reason why you would 113want to do "cvs annotate a-file.c" to begin with. 114 115You would use "cvs annotate" on a file when you have trouble 116with a function (or even a single "if" statement in a function) 117that happens to be defined in the file, which does not do what 118you want it to do. And you would want to find out why it was 119written that way, because you are about to modify it to suit 120your needs, and at the same time you do not want to break its 121current callers. For that, you are trying to find out why the 122original author did things that way in the original context. 123 124Many times, it may be enough to see the commit log messages of 125commits that touch the file in question, possibly along with the 126patches themselves, like this: 127 128 $ git-whatchanged -p a-file.c 129 130This will show log messages and patches for each commit that 131touches a-file. 132 133This, however, may not be very useful when this file has many 134modifications that are not related to the piece of code you are 135interested in. You would see many log messages and patches that 136do not have anything to do with the piece of code you are 137interested in. As an example, assuming that you have this piece 138code that you are interested in in the HEAD version: 139 140 if (frotz) { 141 nitfol(); 142 } 143 144you would use git-rev-list and git-diff-tree like this: 145 146 $ git-rev-list HEAD | 147 git-diff-tree --stdin -v -p -S'if (frotz) { 148 nitfol(); 149 }' 150 151We have already talked about the "--stdin" form of git-diff-tree 152command that reads the list of commits and compares each commit 153with its parents. The git-whatchanged command internally runs 154the equivalent of the above command, and can be used like this: 155 156 $ git-whatchanged -p -S'if (frotz) { 157 nitfol(); 158 }' 159 160When the -S option is used, git-diff-tree command outputs 161differences between two commits only if one tree has the 162specified string in a file and the corresponding file in the 163other tree does not. The above example looks for a commit that 164has the "if" statement in it in a file, but its parent commit 165does not have it in the same shape in the corresponding file (or 166the other way around, where the parent has it and the commit 167does not), and the differences between them are shown, along 168with the commit message (thanks to the -v flag). It does not 169show anything for commits that do not touch this "if" statement. 170 171Also, in the original context, the same statement might have 172appeared at first in a different file and later the file was 173renamed to "a-file.c". CVS annotate would not help you to go 174back across such a rename, but GIT would still help you in such 175a situation. For that, you can give the -C flag to 176git-diff-tree, like this: 177 178 $ git-whatchanged -p -C -S'if (frotz) { 179 nitfol(); 180 }' 181 182When the -C flag is used, file renames and copies are followed. 183So if the "if" statement in question happens to be in "a-file.c" 184in the current HEAD commit, even if the file was originally 185called "o-file.c" and then renamed in an earlier commit, or if 186the file was created by copying an existing "o-file.c" in an 187earlier commit, you will not lose track. If the "if" statement 188did not change across such rename or copy, then the commit that 189does rename or copy would not show in the output, and if the 190"if" statement was modified while the file was still called 191"o-file.c", it would find the commit that changed the statement 192when it was in "o-file.c". 193 194[ BTW, the current versions of "git-diff-tree -C" is not eager 195 enough to find copies, and it will miss the fact that a-file.c 196 was created by copying o-file.c unless o-file.c was somehow 197 changed in the same commit.] 198 199You can use the --pickaxe-all flag in addition to the -S flag. 200This causes the differences from all the files contained in 201those two commits, not just the differences between the files 202that contain this changed "if" statement: 203 204 $ git-whatchanged -p -C -S'if (frotz) { 205 nitfol(); 206 }' --pickaxe-all 207 208[ Side note. This option is called "--pickaxe-all" because -S 209 option is internally called "pickaxe", a tool for software 210 archaeologists.]