Chapter 7. Advanced Topics

If you've been reading this book chapter by chapter, from start to finish, you should by now have acquired enough knowledge to use the Subversion client to perform the most common version control operations. You understand how to checkout a working copy from a Subversion repository. You are comfortable with submitting and receiving changes using the svn commit and svn update functions. You've probably even developed a reflex which causes you to run the svn status command almost unconsciously. For all intents and purposes, you are ready to use Subversion in a typical environment.

But the Subversion feature set doesn't stop at “common version control operations”.

This chapter highlights some of Subversion's features that aren't quite so regularly used. In it, we will discuss Subversion's property (or “metadata”) support, and how to modify Subversion's default behaviors by tweaking its runtime configuration area. We will describe how you can use externals definitions to instruct Subversion to pull data from multiple repositories. We'll cover in detail some of the additional clientand server-side tools that are part of the Subversion distribution.

Before reading this chapter, you should be familiar with the basic file and directory versioning capabilities of Subversion. If you haven't already read about those, or if you need a refresher, we recommend that you check out Chap- ter 2, Basic Concepts and Chapter 3, Guided Tour. Once you've mastered the basics and consumed this chapter, you'll be a Subversion power-user!

Runtime Configuration Area

Subversion provides many optional behaviors that can be controlled by the user. Many of these options are of the kind that a user would wish to apply to all Subversion operations. So, rather than forcing users to remember com- mand-line arguments for specifying these options, and to use them for each and every operation they perform, Subversion uses configuration files, segregated into a Subversion configuration area.

The Subversion configuration area is a two-tiered hierarchy of option names and their values. Usually, this boils down to a special directory that contains configuration files (the first tier), which are just text files in standard INI format (with “sections” providing the second tier). These files can be easily edited using your favorite text editor (such as Emacs or vi), and contain directives read by the client to determine which of several optional behaviors the user prefers.

Configuration Area Layout

The first time that the svn command-line client is executed, it creates a per-user configuration area. On Unix-like systems, this area appears as a directory named .subversion in the user's home directory. On Win32 systems, Subversion creates a folder named Subversion, typically inside the Application Data area of the user's profile directory (which, by the way, is usually a hidden directory). However, on this platform the exact location differs from system to system, and is dictated by the Windows registry. 25 We will refer to the per-user configuration area using its Unix name, .subversion.

In addition to the per-user configuration area, Subversion also recognizes the existence of a system-wide configuration area. This gives system administrators the ability to establish defaults for all users on a given machine. Note that the system-wide configuration area does not alone dictate mandatory policy—the settings in the per-user configuration area override those in the system-wide one, and command-line arguments supplied to the svn program have the final word on behavior. On Unix-like platforms, the system-wide configuration area is expected to be the / etc/subversion directory; on Windows machines, it looks for a Subversion directory inside the common Application Data location (again, as specified by the Windows Registry). Unlike the per-user case, the svn program does not attempt to create the system-wide configuration area.

25The APPDATA environment variable points to the Application Data area, so you can always refer to this folder as

%APPDATA%\Subversion.

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Advanced Topics

The configuration area currently contains three files—two configuration files (config and servers), and a README.txt file which describes the INI format. At the time of their creation, the files contain default values for each of the supported Subversion options, mostly commented out and grouped with textual descriptions about how the values for the key affect Subversion's behavior. To change a certain behavior, you need only to load the appropriate configuration file into a text editor, and modify the desired option's value. If at any time you wish to have the default configuration settings restored, you can simply remove (or rename) your configuration directory and then run some innocuous svn command, such as svn --version. A new configuration directory with the default contents will be created.

The per-user configuration area also contains a cache of authentication data. The auth directory holds a set of subdirectories that contain pieces of cached information used by Subversion's various supported authentication methods. This directory is created in such a way that only the user herself has permission to read its contents.

Configuration and the Windows Registry

In addition to the usual INI-based configuration area, Subversion clients running on Windows platforms may also use the Windows registry to hold the configuration data. The option names and their values are the same as in the INI files. The “file/section” hierarchy is preserved as well, though addressed in a slightly different fashion—in this schema, files and sections are just levels in the registry key tree.

Subversion looks for system-wide configuration values under the

HKEY_LOCAL_MACHINE\Software\Tigris.org\Subversion key. For example, the global-ig- nores option, which is in the miscellany section of the config file, would be found at

HKEY_LOCAL_MACHINE\Software\Tigris.org\Subversion\Config\Miscellany\global-ign ores. Per-user configuration values should be stored under

HKEY_CURRENT_USER\Software\Tigris.org\Subversion.

Registry-based configuration options are parsed before their file-based counterparts, so are overridden by values found in the configuration files. In other words, configuration priority is granted in the following order on a Windows system:

1.Command-line options

2.The per-user INI files

3.The per-user Registry values

4.The system-wide INI files

5.The system-wide Registry values

Also, the Windows Registry doesn't really support the notion of something being “commented out”. However, Subversion will ignore any option key whose name begins with a hash (#) character. This allows you to effectively comment out a Subversion option without deleting the entire key from the Registry, obviously simplifying the process of restoring that option.

The svn command-line client never attempts to write to the Windows Registry, and will not attempt to create a default configuration area there. You can create the keys you need using the REGEDIT program. Alternatively, you can create a .reg file, and then double-click on that file from the Explorer shell, which will cause the data to be merged into your registry.

Example 7.1. Sample Registration Entries (.reg) File.

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