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# Handling binary files

There are two issues with using CVS to store binary files. The first is that CVS by default convert 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. If you are using an old version of RCS without this option, and you are using an operating system, such as unix, which terminates lines with linefeeds only, you can use ``-ko'` instead; if you are on another operating system, upgrade to a version of RCS, such as 5.7 or later, which supports ``-kb'`.

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
    $ cvs commit -m "make it binary" kotest  # For non-unix systems

When you check in the file ``kotest'` the keywords are expanded. (Try the above example, and do a `cat kotest` after every command). 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. The easiest way to get the unexpanded version of ``kotest'` is `cvs update -A`. If you need to cope with line endings (that is, you are using a CVS client 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.

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.

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