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(cvsbook.info)Checking Out A Working Copy

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Checking Out A Working Copy
---------------------------

The command to check out a project is exactly what you think it is:

     floss$ cvs checkout myproj
     cvs checkout: Updating myproj
     U myproj/README.txt
     U myproj/hello.c
     cvs checkout: Updating myproj/a-subdir
     U myproj/a-subdir/whatever.c
     cvs checkout: Updating myproj/a-subdir/subsubdir
     U myproj/a-subdir/subsubdir/fish.c
     cvs checkout: Updating myproj/b-subdir
     U myproj/b-subdir/random.c
     
     floss$ ls
     myproj/      was_myproj/
     floss$ cd myproj
     floss$ ls
     CVS/        README.txt  a-subdir/   b-subdir/   hello.c
     floss$

Behold - your first working copy! Its contents are exactly the same as
what you imported, with the addition of a subdirectory named "CVS".
That's where CVS stores version control information.  Actually, each
directory in the project has a CVS subdirectory:

     floss$ ls a-subdir
     CVS/        subsubdir/  whatever.c
     floss$ ls a-subdir/subsubdir/
     CVS/    fish.c
     floss$ ls b-subdir
     CVS/      random.c

The fact that CVS keeps its revision information in subdirectories named
CVS means that your project can never contain subdirectories of its own
named CVS.  In practice, I've never heard of this being a problem.

Before editing any files, let's take a peek inside the black box:

     floss$ cd CVS
     floss$ ls
     Entries     Repository  Root
     floss$ cat Root
     /usr/local/cvs
     floss$ cat Repository
     myproj
     floss$

Nothing too mysterious there.  The Root file points to repository, and
the Repository file points to a project inside the repository.  If
that's a little confusing, let me explain.

There is a longstanding confusion about terminology in CVS.  The word
"repository" is used to refer to two different things.  Sometimes, it
means the root directory of a repository (for example, /usr/local/cvs),
which can contain many projects; this is what the Root file refers to.
But other times, it means one particular project-specific subdirectory
within a repository root (for example, /usr/local/cvs/myproj,
/usr/local/cvs/yourproj, or /usr/local/cvs/fish).  The Repository file
inside a CVS subdirectory takes the latter meaning.

In this book, "repository" generally means Root (that is, the top-level
repository), although it may occasionally be used to mean a
project-specific subdirectory.  If the intended sense can't be figured
out from the context, there will be clarifying text.  Note that the
Repository file may sometimes contain an absolute path to the project
name instead of a relative path.  This can make it slightly redundant
with the Root file:

     floss$ cd CVS
     floss$ cat Root
     :pserver:jrandom@cvs.foobar.com:/usr/local/cvs
     floss$ cat Repository
     /usr/local/cvs/myproj
     floss$

The Entries file stores information about the individual files in the
project.  Each line deals with one file, and there are only lines for
files or subdirectories in the immediate parent directory.  Here's the
top-level CVS/Entries file in myproj:

     floss$ cat Entries
     /README.txt/1.1.1.1/Sun Apr 18 18:18:22 1999//
     /hello.c/1.1.1.1/Sun Apr 18 18:18:22 1999//
     D/a-subdir////
     D/b-subdir////

The format of each line is

     /filename/revision number/last modification date//

and the directory lines are prefixed with "D". (CVS doesn't really keep
a change history for directories, so the fields for revision number and
datestamp are empty.)

The datestamps record the date and time of the last update (in Universal
Time, not local time) of the files in the working copy.  That way, CVS
can easily tell whether a file has been modified since the last
checkout, update, or commit.  If the file system timestamp differs from
the timestamp in the CVS/Entries file, CVS knows (without even having to
consult the repository) that the file was probably modified.

If you take a look at the CVS/* files in one of the subdirectories

     floss$ cd a-subdir/CVS
     floss$ cat Root
     /usr/local/cvs
     floss$ cat Repository
     myproj/a-subdir
     floss$ cat Entries
     /whatever.c/1.1.1.1/Sun Apr 18 18:18:22 1999//
     D/subsubdir////
     floss$

you can see that the root repository has not changed, but the Repository
file spells out the location of this subdirectory of the project, and
the Entries file contains different lines.

Immediately after import, the revision number of every file in the
project is shown as 1.1.1.1.  This initial revision number is a bit of a
special case, so we won't examine it in detail just yet; we'll take a
closer look at revision numbers after we've committed some changes.