9.2 How to store binary files

There are two issues with using CVS to store binary files. The first is that CVS by default converts line endings between the canonical form in which they are stored in the repository (linefeed only), and the form appropriate to the operating system in use on the client (for example, carriage return followed by line feed for Windows NT).

The second is that a binary file might happen to contain data which looks like a keyword (see section Keyword substitution), so keyword expansion must be turned off.

The ‘-kb’ option available with some CVS commands insures that neither line ending conversion nor keyword expansion will be done.

Here is an example of how you can create a new file using the ‘-kb’ flag:

$ echo '$Id$' > kotest
$ cvs add -kb -m"A test file" kotest
$ cvs ci -m"First checkin; contains a keyword" kotest

If a file accidentally gets added without ‘-kb’, one can use the cvs admin command to recover. For example:

$ echo '$Id$' > kotest
$ cvs add -m"A test file" kotest
$ cvs ci -m"First checkin; contains a keyword" kotest
$ cvs admin -kb kotest
$ cvs update -A kotest
# For non-unix systems:
# Copy in a good copy of the file from outside CVS
$ cvs commit -m "make it binary" kotest

When you check in the file ‘kotest’ the file is not preserved as a binary file, because you did not check it in as a binary file. The cvs admin -kb command sets the default keyword substitution method for this file, but it does not alter the working copy of the file that you have. If you need to cope with line endings (that is, you are using CVS on a non-unix system), then you need to check in a new copy of the file, as shown by the cvs commit command above. On unix, the cvs update -A command suffices. (Note that you can use cvs log to determine the default keyword substitution method for a file and cvs status to determine the keyword substitution method for a working copy.)

However, in using cvs admin -k to change the keyword expansion, be aware that the keyword expansion mode is not version controlled. This means that, for example, that if you have a text file in old releases, and a binary file with the same name in new releases, CVS provides no way to check out the file in text or binary mode depending on what version you are checking out. There is no good workaround for this problem.

You can also set a default for whether cvs add and cvs import treat a file as binary based on its name; for example you could say that files who names end in ‘.exe’ are binary. See section The cvswrappers file. There is currently no way to have CVS detect whether a file is binary based on its contents. The main difficulty with designing such a feature is that it is not clear how to distinguish between binary and non-binary files, and the rules to apply would vary considerably with the operating system.