02 -- Managing Files with FileLists

Chapter 2—Managing Files with FileLists

Handling Common Actions

Rake is a tool for controlling builds. In this part of the Rake tutorial, we see how to organize the Rake actions to apply to many similar tasks.

In the previous chapter, we talked about the basics of specifying dependencies and associating actions to build the files. We ended up with a nice Rakefile that built our simple C program, but with some duplication in the build rules.

But First, Some Extra Rake Targets

But before we get into all that, lets add some convience targets to our Rakefile. First of all, it would be nice to have a default target that is invoked when we don’t give any explicit task names to rake. The default target looks like this:

Rakefile Fragment

1 task :default => ["hello"]

Until now, the only kind of task we have seen in Rake are file tasks. File tasks are knowledgable about time stamps on files. A file task will not execute its action unless the file it represents doesn’t exist, or is older than any of its prerequisites.

A non-file task (or just plain “task”) does not represent the creation of a file. Since there is no timestamp for comparison, non-file tasks always execute their actions (if they have any). Since the default task does not represent a file named “default”, we use a regular non-file task for this purpose. Non-file tasks just use the task keyword (instead of the file keyword).

Here are a couple of other really useful tasks that I almost always include in a Rakefile.

Remove temporary files created during the build process.

Remove all files generated during the build process.

clean tidies up the directories and removes any files that generated as part of the build process, but are not the final goal of the build process. For example, the .o files used to link up the final executable hello program would fall in this category. After the executable program is built, the .o files are no longer needed and will be removed by saying “rake clean”.

clobber is like clean, but even more aggressive. “rake clobber” will remove all files that are not part of the original package. It should return a project to the “just checked out of CVS” state. So it removes the final executable program as well as the files removed by clean.

In fact, these tasks are so common, Rake comes with a predefined library that implements clean and clobber.

But every project is different, how do we specify which files are to be cleaned and clobbered on a per project basis?

The answer is File lists.

File Lists to the Rescue

A file list is simply a list of file names. Since a lot of what Rake does involves files and lists of those files, a file list has some special features to make manipulating file names rather easy.

Suppose you want a list of all the C files in your project. You could add this to your rake file:

Rakefile Fragment

1 SRC = FileList['*.c']

This will collect all the files ending in ”.c” in the top level directory of your project. File lists understand glob patterns (i.e. things like ".c") and will find all the matching files.

Rakefile Fragment*

1 CLEAN = FileList['*.o']

(CLEAN is the file list associated with the clean task. I’ll let you guess the name of the file list associated with clobber).