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The Fast Method Of Reverting

The fast, fancy way of reverting is to use the -j (for "join") flag to the update command. This flag is like -r in that it takes a revision number, and you can use up to two -j's at once. CVS calculates the difference between the two named revisions and applies that difference as a patch to the file in question (so the order in which you give the revisions is important).

Thus, assuming qsmith's copy is up to date, he can just do this:

     paste$ cvs update -j 1.4 -j 1.3 hello.c
     RCS file: /usr/local/cvs/myproj/hello.c,v
     retrieving revision 1.4
     retrieving revision 1.3
     Merging differences between 1.4 and 1.3 into hello.c
     paste$ cvs update
     cvs update: Updating .
     M hello.c
     cvs update: Updating a-subdir
     cvs update: Updating a-subdir/subsubdir
     cvs update: Updating b-subdir
     paste$ cvs ci -m "reverted to 1.3 code" hello.c
     Checking in hello.c;
     /usr/local/cvs/myproj/hello.c,v  <--  hello.c
     new revision: 1.5; previous revision: 1.4

When you only need to revert one file, there's not really much difference between the plodding and fast methods. Later in the book, you'll see how the fast method is much better for reverting multiple files at once. In the meantime, use whichever way you're more comfortable with.

Reverting Is Not A Substitute For Communication

In all likelihood, what qsmith did in our example was quite rude. When you're working on a real project with other people and you think that someone has committed a bad change, the first thing you should do is talk to him or her about it. Maybe there's a good reason for the change, or maybe he or she just didn't think things through. Either way, there's no reason to rush and revert. A full record of everything that happens is stored permanently in CVS, so you can always revert to a previous revision after consulting with whoever made the changes.

If you're a project maintainer facing a deadline or you feel you have the right and the need to revert the change unconditionally, then do so – but follow it immediately with an email to the author whose change was reverted, explaining why you did it and what needs to be fixed to recommit the change.

Karl Fogel wrote this book. Buy a printed copy via his homepage at

copyright  ©  January 18 2019 sean dreilinger url: