The coolness that is Rake

Rake is cool enough as a build tool, but wait until you check out its library.

First off, if you use make or ant, you owe it to yourself to look into Rake. The syntax is so much more readable than either, and you have a full-fledged programming language right there in your build script. The docs have a concise introduction to Rakefiles; Martin Fowler has a longer article called “Using the Rake Build Language“.

But wait! There’s more!

So Rake’s documentation is pretty sketchy. Mention is made of some cool libraries that ship with it, but no details. So I decided to RTFS, and I found much of coolness.

Coolness #1: All the coolness comes right out of the box. You don’t even need to require anything from your rakefile (unless you’re doing really fancy stuff). Just write a rakefile containing some tasks, run rake, and you’re off and running.

Coolness #2: They add an ext() method to the String class. Treats the string as a filename; returns a new filename with the extension changed to whatever you specify. Equivalent to Delphi’s ChangeFileExt() or .NET’s Path.ChangeExtension. Something that’s sorely lacking from Ruby out of the box.

Coolness #3: A built-in command to shell out to Ruby. They have a method to shell out, and another one specifically to shell out to another Ruby process.

When you want to shell out (e.g. to run your compiler), you should use the sh() and ruby() methods, which will automatically fail the task if the process returns a nonzero exit code. (By default, the value returned by a task block is ignored; if you want to fail the task, you need to do it explicitly with fail() or raise or some such, or call something like sh() that does it for you.)

rule '.rb' => ['.y'] do |t|
  sh "racc", t.source, "-o",
task :test do
  ruby "test_all.rb"

Coolness #4: Built-in support for running unit tests. I already wrote a test_all.rb, but if I’d looked at Rake, I wouldn’t have had to. This works just as well:

[Note: It turns out that this sample code isn’t the right way to do it; see this post for corrected code. Still the same number of lines, just better-behaved.]

require 'rake/runtest'
task :test do
  Rake.run_tests "**/*tests.rb"

If you follow their convention of having your tests in test/test*.rb, you don’t need to pass an argument to Rake.run_tests at all. I like my tests to be next to the files they’re testing, so the above example is what I prefer.

There’s also a TestTask if you want fancier options, like modifying your $LOAD_PATH before running the test. (TestTask actually launches a new Ruby process via the ruby() method; Rake.run_tests runs them in-process.)

Coolness #5: FileList.

FileList is a list of files, much like an array. But instead of giving it individual filenames, you can give it patterns, like ‘lib/**/*’, and it comes back as an array of matching filenames. (It can take both include and exclude patterns.) It lazy-initializes its contents, so if you create a FileList but then don’t run the task that uses it, it’s basically free. By default, it ignores CVS and .svn directories.

But coolest of all, FileList has shorthand methods: sub(), gsub(), ext(), egrep(). Want to return a new copy of a FileList with all the extensions changed? No sweat. Want to grep through every file in a FileList, and do something with each file whose contents match a given regex? egrep() to the rescue. I may never again have to write six whole lines of code to recursively grep through a directory tree of source files.

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