In any given working copy there is a good chance that alongside all those versioned files and directories are other files and directories which are neither versioned nor intended to be. Text editors litter directories with backup files. Software compilers generate intermediate—or even final—files which you typically wouldn't bother to version. And users themselves drop various other files and directories wherever they see fit, often in version control working copies.

It's ludicrous to expect Subversion working copies to be somehow impervious to this kind of clutter and impurity. In fact, Subversion counts it as a feature that its working copies are just typical directories, just like unversioned trees. But these not-to-be-versioned files and directories can cause some annoyance for Subversion users. For example, because the svn add and svn import commands act recursively by default, and don't know which files in a given tree you do and don't wish to version, it's easy to accidentally add stuff to version control that you didn't mean to. And because svn status reports, by default, every item of interest in a working copy—including unversioned files and directories—its output can get quite noisy where many of these things exist.

So Subversion provides two ways for telling it which files you would prefer that it simply disregard. One of the ways involves the use of Subversion's runtime configuration system (see the section called “Runtime Configuration Area”), and therefore applies to all the Subversion operations which make use of that runtime configuration, generally those performed on a particular computer, or by a particular user of a computer. The other way makes use of Subversion's directory property support, is more tightly bound to the versioned tree itself, and therefore affects everyone who has a working copy of that tree. Both of the mechanisms use file patterns.

The Subversion runtime configuration system provides an option, global-ignores, whose value is a whitespace-delimited collection of file patterns (also known as globs). The Subversion client checks these patterns against the names of the files which are candidates for addition to version control, as well as to unversioned files which the svn status command notices. If any file's name matches one of the patterns, Subversion will basically act as if the file didn't exist at all. This is really useful for the kinds of files that you almost never want to version, such as editor backup files like Emacs' *~ and .*~ files.

When found on a versioned directory, the svn:ignore property is expected to contain a list of newline-delimited file patterns which Subversion should use to determine ignorable objects in that same directory. These patterns do not override those found in the global-ignores runtime configuration option, but are instead appended to that list. And it's worth noting again that, unlike the global-ignores option, the patterns found in the svn:ignore property apply only to the directory on which that property is set, and not to any of its subdirectories. The svn:ignore property is a good way to tell Subversion to ignore files that are likely to be present in every user's working copy of that directory, such as compiler output or—to use an example more appropriate to this book—the HTML, PDF, or PostScript files generated as the result of a conversion of some source DocBook XML files to a more legible output format.

$ svn propset svn:ignore -F .cvsignore .
property 'svn:ignore' set on '.'
$

The global list of ignore patterns tends to be more a matter of personal taste, and tied more closely to a user's particular tool chain than to the details of any particular working copy's needs. So, the rest of this section will focus on the svn:ignore property and its uses.

Say you have the following output from svn status:

$ svn status calc
 M     calc/button.c
?      calc/calculator
?      calc/data.c
?      calc/debug_log
?      calc/debug_log.1
?      calc/debug_log.2.gz
?      calc/debug_log.3.gz

In this example, you have made some property modifications to button.c, but in your working copy you also have some unversioned files: the latest calculator program that you've compiled from your source code, a source file named data.c, and a set of debugging output log files. Now, you know that your build system always results in the calculator program being generated. ^[13] And you know that your test suite always leaves those debugging log files lying around. These facts are true for all working copies of this project, not just your own. And you know that you aren't interested in seeing those things every time you run svn status, and pretty sure that nobody else is interested in them either. So you use svn propedit svn:ignore calc to add some ignore patterns to the calc directory. For example, you might add this as the new value of the svn:ignore property:

calculator
debug_log*

After you've added this property, you will now have a local property modification on the calc directory. But notice what else is different about your svn status output:

$ svn status
 M     calc
 M     calc/button.c
?      calc/data.c

Now, all that cruft is missing from the output! Of course, your calculator compiled program and all those logfiles are still in your working copy. Subversion is simply not reminding you that they are present and unversioned. And now with all the uninteresting noise removed from the display, you are left with more interesting items—such as that source code file data.c that you probably forgot to add to version control.

Of course, this less-verbose report of your working copy status isn't the only one available. If you actually want to see the ignored files as part of the status report, you can pass the --no-ignore option to Subversion:

$ svn status --no-ignore
 M     calc
 M     calc/button.c
I      calc/calculator
?      calc/data.c
I      calc/debug_log
I      calc/debug_log.1
I      calc/debug_log.2.gz
I      calc/debug_log.3.gz

As mentioned earlier, the list of file patterns to ignore is also used by svn add and svn import. Both of these operations involve asking Subversion to begin managing some set of files and directories. Rather than force the user to pick and choose which files in a tree she wishes to start versioning, Subversion uses the ignore patterns—both the global and the per-directory lists—to determine which files should not be swept into the version control system as part of a larger recursive addition or import operation. And here again, you can use the --no-ignore option to tell Subversion ignore its ignores list and operate on all the files and directories present.