CS253: Software Development with C++

Spring 2018

Subversion

Subversion (svn) Lab

Chill

Yes, there are newer systems than Subversion. They’re probably better. It doesn’t matter. The goal is to understand how such systems work. They're all essentially the same. Don’t get hung up on details.

Description

In the bad old days, it was difficult to keep track of source code when several people were working on the large project. Generally, a master copy of the source was kept somewhere, and you just had to be careful when you made changes. You had to make sure that Bill’s latest change didn’t replace Elizabeth’s recent bug fix. What if you made a bad change? You hoped that you had a backup tape. It wasn’t a very good system.

In this lab, we will use Subversion, which is a system of source code management. It’s used to maintain the history of software changes (or any other file, for that matter), and to permit multiple developers to collaborate on a large project.

Think of it this way: somebody creates an svn repository, somewhere. It contains a number of files and directories. Often, this will be a large open-source software project. Using svn, you check out a copy of these files (like checking out books from a library, except that this is a copy). You can also:

You access this repository in a variety of ways: using ssh, using local file access, etc.

Subversion clients are free, and exist for Windows, Linux, Mac, you-name-it.

Subversion commands are generally like this:

svn subcommand optional-filename

Using a remote svn repository via https

First, we will use svn to examine the svn repository that holds the source code for the svn command itself. These operations may be slow, depending on how full the intertubes are at the moment.

  1. Make an empty directory somewhere
  2. cd into it
  3. Check out a small subdirectory of the svn repository:
    svn co https://svn.apache.org/repos/asf/subversion/trunk/doc/
    This will create the directory doc, which will contain a number of files, and another directory.
  4. cd doc
  5. ls -l
  6. See the history of the file README:
    svn log README | more

Using a local svn repository

Instructor, recreate ~cs253/pub/svntest as needed:

    cd ~cs253/pub
    rm -rf svntest
    tar -xvpf svntest.txz

Let’s use a local svn repository, for the sake of speed. I’ve created one in a subdirectory of cs253’s home directory: /s/bach/a/class/cs253/pub/svntest

Everybody, do these steps:

  1. Make a different empty directory somewhere
  2. cd into it
  3. Check out the repository:
    svn co file:///s/bach/a/class/cs253/pub/svntest/calc
  4. cd calc
  5. ls -l
  6. svn log README

The instructor will now change a file in the repository:

Now, everybody update their own copies:

You ought to see something like this:

U    README
Updated to revision <number>.

Notice how you haven’t had to specify that awful file:///s/bach/… path since first checking out the repository. Hooray!

What about conflicting changes?

When you do svn ci, it will attempt to check in any files that you’ve modified. If somebody else has changed the repository version of that file after you checked yours out, then svi ci or svi update will give you an error message, and present a number of options.

With the help of a student, the instructor will now create such a situation:

  1. Student does svn update
  2. instructor does svn update
  3. Student changes a file, and does svn ci
  4. Instructor changes a file, and tries to do svi ci.

See https://svnbook.red-bean.com/nightly/en/svn.tour.cycle.html#svn.tour.cycle.resolve for more information on how conflict resolution works.

Create & use your own repository

  1. Break up into groups of three.
  2. The first student should do these commands to create a repository:
    CommandExplanation
    hostnameWhat system am I running on?
    svnadmin create /tmp/rep Use some other name if /tmp/rep already exists
    chmod -R a=rwx /tmp/rep  allow all users to modify the repository
  3. The second student should do these commands from another computer to add a file to the repository:
    CommandExplanation
    cd $(mktemp -d)go into a temporary directory
    svn co svn+ssh://host///tmp/repInstead of host, use the hostname discovered above
    cd repgo into that directory
    date >nowcreate a data file
    svn add nowadd it to the repository
    svn ci nowcheck in the current version
    svn log nowSee what changes have been made to now
  4. The third student should do these commands from a third computer to change that new file:
    CommandExplanation
    cd $(mktemp -d)go into a temporary directory
    svn co svn+ssh://host///tmp/repInstead of host, use the hostname discovered above
    cd repgo into that directory
    gedit nowchange now using an editor you like
    svn ci nowcheck in the current version
    svn log nowSee what changes have been made to now
    Repeat until you’re comfortable with adding and modifying files. Use svn update to get your copy of the repository up to date after another student makes a change.
  5. When you’re done, clean up: rm -rf /tmp/rep

What else?

There are many aspects to svn that haven’t been covered. Do svn help for an overview, and svn help subcommand for information on any of the svn subcommands. Some of my favorites:

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Modified: 2018-04-14T21:53

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