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+= Rakefile Format (as of version 0.8.7)
+
+First of all, there is no special format for a Rakefile. A Rakefile
+contains executable Ruby code. Anything legal in a ruby script is
+allowed in a Rakefile.
+
+Now that we understand there is no special syntax in a Rakefile, there
+are some conventions that are used in a Rakefile that are a little
+unusual in a typical Ruby program. Since a Rakefile is tailored to
+specifying tasks and actions, the idioms used in a Rakefile are
+designed to support that.
+
+So, what goes into a Rakefile?
+
+== Tasks
+
+Tasks are the main unit of work in a Rakefile. Tasks have a name
+(usually given as a symbol or a string), a list of prerequisites (more
+symbols or strings) and a list of actions (given as a block).
+
+=== Simple Tasks
+
+A task is declared by using the +task+ method. +task+ takes a single
+parameter that is the name of the task.
+
+ task :name
+
+=== Tasks with Prerequisites
+
+Any prerequisites are given as a list (enclosed in square brackets)
+following the name and an arrow (=>).
+
+ task :name => [:prereq1, :prereq2]
+
+<b>NOTE:</b> Although this syntax looks a little funky, it is legal
+Ruby. We are constructing a hash where the key is :name and the value
+for that key is the list of prerequisites. It is equivalent to the
+following ...
+
+ hash = Hash.new
+ hash[:name] = [:prereq1, :prereq2]
+ task(hash)
+
+=== Tasks with Actions
+
+Actions are defined by passing a block to the +task+ method. Any Ruby
+code can be placed in the block. The block may reference the task
+object via the block parameter.
+
+ task :name => [:prereq1, :prereq2] do |t|
+ # actions (may reference t)
+ end
+
+=== Multiple Definitions
+
+A task may be specified more than once. Each specification adds its
+prerequisites and actions to the existing definition. This allows one
+part of a rakefile to specify the actions and a different rakefile
+(perhaps separately generated) to specify the dependencies.
+
+For example, the following is equivalent to the single task
+specification given above.
+
+ task :name
+ task :name => [:prereq1]
+ task :name => [:prereq2]
+ task :name do |t|
+ # actions
+ end
+
+== File Tasks
+
+Some tasks are designed to create a file from one or more other files.
+Tasks that generate these files may be skipped if the file already
+exists. File tasks are used to specify file creation tasks.
+
+File tasks are declared using the +file+ method (instead of the +task+
+method). In addition, file tasks are usually named with a string
+rather than a symbol.
+
+The following file task creates a executable program (named +prog+)
+given two object files name <tt>a.o</tt> and <tt>b.o</tt>. The tasks
+for creating <tt>a.o</tt> and <tt>b.o</tt> are not shown.
+
+ file "prog" => ["a.o", "b.o"] do |t|
+ sh "cc -o #{t.name} #{t.prerequisites.join(' ')}"
+ end
+
+== Directory Tasks
+
+It is common to need to create directories upon demand. The
++directory+ convenience method is a short-hand for creating a FileTask
+that creates the directory. For example, the following declaration
+...
+
+ directory "testdata/examples/doc"
+
+is equivalent to ...
+
+ file "testdata" do |t| mkdir t.name end
+ file "testdata/examples" do |t| mkdir t.name end
+ file "testdata/examples/doc" do |t| mkdir t.name end
+
+The +directory+ method does not accept prerequisites or actions, but
+both prerequisites and actions can be added later. For example ...
+
+ directory "testdata"
+ file "testdata" => ["otherdata"]
+ file "testdata" do
+ cp Dir["standard_data/*.data"], "testdata"
+ end
+
+== Tasks with Parallel Prerequisites
+
+Rake allows parallel execution of prerequisites using the following syntax:
+
+ multitask :copy_files => [:copy_src, :copy_doc, :copy_bin] do
+ puts "All Copies Complete"
+ end
+
+In this example, +copy_files+ is a normal rake task. Its actions are
+executed whenever all of its prerequisites are done. The big
+difference is that the prerequisites (+copy_src+, +copy_bin+ and
++copy_doc+) are executed in parallel. Each of the prerequisites are
+run in their own Ruby thread, possibly allowing faster overall runtime.
+
+=== Secondary Prerequisites
+
+If any of the primary prerequisites of a multitask have common secondary
+prerequisites, all of the primary/parallel prerequisites will wait
+until the common prerequisites have been run.
+
+For example, if the <tt>copy_<em>xxx</em></tt> tasks have the
+following prerequisites:
+
+ task :copy_src => [:prep_for_copy]
+ task :copy_bin => [:prep_for_copy]
+ task :copy_doc => [:prep_for_copy]
+
+Then the +prep_for_copy+ task is run before starting all the copies in
+parallel. Once +prep_for_copy+ is complete, +copy_src+, +copy_bin+,
+and +copy_doc+ are all run in parallel. Note that +prep_for_copy+ is
+run only once, even though it is referenced in multiple threads.
+
+=== Thread Safety
+
+The Rake internal data structures are thread-safe with respect
+to the multitask parallel execution, so there is no need for the user
+to do extra synchronization for Rake's benefit. However, if there are
+user data structures shared between the parallel prerequisites, the
+user must do whatever is necessary to prevent race conditions.
+
+== Tasks with Arguments
+
+Prior to version 0.8.0, rake was only able to handle command line
+arguments of the form NAME=VALUE that were passed into Rake via the
+ENV hash. Many folks had asked for some kind of simple command line
+arguments, perhaps using "--" to separate regular task names from
+argument values on the command line. The problem is that there was no
+easy way to associate positional arguments on the command line with
+different tasks. Suppose both tasks :a and :b expect a command line
+argument: does the first value go with :a? What if :b is run first?
+Should it then get the first command line argument.
+
+Rake 0.8.0 solves this problem by explicitly passing values directly
+to the tasks that need them. For example, if I had a release task
+that required a version number, I could say:
+
+ rake release[0.8.2]
+
+And the string "0.8.2" will be passed to the :release task. Multiple
+arguments can be passed by separating them with a comma, for example:
+
+ rake name[john,doe]
+
+Just a few words of caution. The rake task name and its arguments
+need to be a single command line argument to rake. This generally
+means no spaces. If spaces are needed, then the entire rake +
+argument string should be quoted. Something like this:
+
+ rake "name[billy bob, smith]"
+
+(Quoting rules vary between operating systems and shells, so make sure
+you consult the proper docs for your OS/shell).
+
+=== Tasks Arguments and the Environment
+
+Task argument values can also be picked up from the environment. For
+example, if the "release" task expected a parameter named
+"release_version", then either
+
+ rake release[0.8.2]
+
+or
+
+ RELEASE_VERSION rake release
+
+will work. Environment variable names must either match the task
+parameter exactly, or match an all-uppercase version of the task
+parameter.
+
+=== Tasks that Expect Parameters
+
+Parameters are only given to tasks that are setup to expect them. In
+order to handle named parameters, the task declaration syntax for
+tasks has been extended slightly.
+
+For example, a task that needs a first name and last name might be
+declared as:
+
+ task :name, [:first_name, :last_name]
+
+The first argument is still the name of the task (:name in this case).
+The next two arguments are the names of the parameters expected by
+:name in an array (:first_name and :last_name in the example).
+
+To access the values of the parameters, the block defining the task
+behaviour can now accept a second parameter:
+
+ task :name, [:first_name, :last_name] do |t, args|
+ puts "First name is #{args.first_name}"
+ puts "Last name is #{args.last_name}"
+ end
+
+The first argument of the block "t" is always bound to the current
+task object. The second argument "args" is an open-struct like object
+that allows access to the task arguments. Extra command line
+arguments to a task are ignored. Missing command line arguments are
+picked up from matching environment variables. If there are no
+matching environment variables, they are given the nil value.
+
+If you wish to specify default values for the arguments, you can use
+the with_defaults method in the task body. Here is the above example
+where we specify default values for the first and last names:
+
+ task :name, [:first_name, :last_name] do |t, args|
+ args.with_defaults(:first_name => "John", :last_name => "Dough")
+ puts "First name is #{args.first_name}"
+ puts "Last name is #{args.last_name}"
+ end
+
+=== Tasks that Expect Parameters and Have Prerequisites
+
+Tasks that use parameters have a slightly different format for
+prerequisites. Use the arrow notation to indicate the prerequisites
+for tasks with arguments. For example:
+
+ task :name, [:first_name, :last_name] => [:pre_name] do |t, args|
+ args.with_defaults(:first_name => "John", :last_name => "Dough")
+ puts "First name is #{args.first_name}"
+ puts "Last name is #{args.last_name}"
+ end
+
+=== Deprecated Task Parameters Format
+
+There is an older format for declaring task parameters that omitted
+the task argument array and used the :needs keyword to introduce the
+dependencies. That format is still supported for compatibility, but
+is not recommended for use. The older format may be dropped in future
+versions of rake.
+
+== Accessing Task Programmatically
+
+Sometimes it is useful to manipulate tasks programmatically in a
+Rakefile. To find a task object, use the <tt>:[]</tt> operator on the
+<tt>Rake::Task</tt>.
+
+=== Programmatic Task Example
+
+For example, the following Rakefile defines two tasks. The :doit task
+simply prints a simple "DONE" message. The :dont class will lookup
+the doit class and remove (clear) all of its prerequisites and
+actions.
+
+ task :doit do
+ puts "DONE"
+ end
+
+ task :dont do
+ Rake::Task[:doit].clear
+ end
+
+Running this example:
+
+ $ rake doit
+ (in /Users/jim/working/git/rake/x)
+ DONE
+ $ rake dont doit
+ (in /Users/jim/working/git/rake/x)
+ $
+
+The ability to programmatically manipulate tasks gives rake very
+powerful meta-programming capabilities w.r.t. task execution, but
+should be used with cation.
+
+== Rules
+
+When a file is named as a prerequisite, but does not have a file task
+defined for it, Rake will attempt to synthesize a task by looking at a
+list of rules supplied in the Rakefile.
+
+Suppose we were trying to invoke task "mycode.o", but no task is
+defined for it. But the rakefile has a rule that look like this ...
+
+ rule '.o' => ['.c'] do |t|
+ sh "cc #{t.source} -c -o #{t.name}"
+ end
+
+This rule will synthesize any task that ends in ".o". It has a
+prerequisite a source file with an extension of ".c" must exist. If
+Rake is able to find a file named "mycode.c", it will automatically
+create a task that builds "mycode.o" from "mycode.c".
+
+If the file "mycode.c" does not exist, rake will attempt
+to recursively synthesize a rule for it.
+
+When a task is synthesized from a rule, the +source+ attribute of the
+task is set to the matching source file. This allows us to write
+rules with actions that reference the source file.
+
+=== Advanced Rules
+
+Any regular expression may be used as the rule pattern. Additionally,
+a proc may be used to calculate the name of the source file. This
+allows for complex patterns and sources.
+
+The following rule is equivalent to the example above.
+
+ rule( /\.o$/ => [
+ proc {|task_name| task_name.sub(/\.[^.]+$/, '.c') }
+ ]) do |t|
+ sh "cc #{t.source} -c -o #{t.name}"
+ end
+
+<b>NOTE:</b> Because of a _quirk_ in Ruby syntax, parenthesis are
+required on *rule* when the first argument is a regular expression.
+
+The following rule might be used for Java files ...
+
+ rule '.java' => [
+ proc { |tn| tn.sub(/\.class$/, '.java').sub(/^classes\//, 'src/') }
+ ] do |t|
+ java_compile(t.source, t.name)
+ end
+
+<b>NOTE:</b> +java_compile+ is a hypothetical method that invokes the
+java compiler.
+
+== Importing Dependencies
+
+Any ruby file (including other rakefiles) can be included with a
+standard Ruby +require+ command. The rules and declarations in the
+required file are just added to the definitions already accumulated.
+
+Because the files are loaded _before_ the rake targets are evaluated,
+the loaded files must be "ready to go" when the rake command is
+invoked. This make generated dependency files difficult to use. By
+the time rake gets around to updating the dependencies file, it is too
+late to load it.
+
+The +Rake.import+ command addresses this by specifying a file to be
+loaded _after_ the main rakefile is loaded, but _before_ any targets
+on the command line are invoked. In addition, if the file name
+matches an explicit task, that task is invoked before loading the
+file. This allows dependency files to be generated and used in a
+single rake command invocation.
+
+<b>NOTE:</b> Starting in Rake version 0.9.0, the top level +import+
+command is deprecated and we recommend using the scoped
+"+Rake.import+" command mentioned above. Future versions of Rake will
+drop support for the top level +import+ command.
+
+=== Example:
+
+ require 'rake/loaders/makefile'
+
+ file ".depends.mf" => [SRC_LIST] do |t|
+ sh "makedepend -f- -- #{CFLAGS} -- #{t.prerequisites} > #{t.name}"
+ end
+
+ Rake.import ".depends.mf"
+
+If ".depends" does not exist, or is out of date w.r.t. the source
+files, a new ".depends" file is generated using +makedepend+ before
+loading.
+
+== Comments
+
+Standard Ruby comments (beginning with "#") can be used anywhere it is
+legal in Ruby source code, including comments for tasks and rules.
+However, if you wish a task to be described using the "-T" switch,
+then you need to use the +desc+ command to describe the task.
+
+=== Example:
+
+ desc "Create a distribution package"
+ task :package => [ ... ] do ... end
+
+The "-T" switch (or "--tasks" if you like to spell things out) will
+display a list of tasks that have a description. If you use +desc+ to
+describe your major tasks, you have a semi-automatic way of generating
+a summary of your Rake file.
+
+ traken$ rake -T
+ (in /home/.../rake)
+ rake clean # Remove any temporary products.
+ rake clobber # Remove any generated file.
+ rake clobber_rdoc # Remove rdoc products
+ rake contrib_test # Run tests for contrib_test
+ rake default # Default Task
+ rake install # Install the application
+ rake lines # Count lines in the main rake file
+ rake rdoc # Build the rdoc HTML Files
+ rake rerdoc # Force a rebuild of the RDOC files
+ rake test # Run tests
+ rake testall # Run all test targets
+
+Only tasks with descriptions will be displayed with the "-T" switch.
+Use "-P" (or "--prereqs") to get a list of all tasks and their
+prerequisites.
+
+== Namespaces
+
+As projects grow (and along with it, the number of tasks), it is
+common for task names to begin to clash. For example, if you might
+have a main program and a set of sample programs built by a single
+Rakefile. By placing the tasks related to the main program in one
+namespace, and the tasks for building the sample programs in a
+different namespace, the task names will not will not interfere with
+each other.
+
+For example:
+
+ namespace "main" do
+ task :build do
+ # Build the main program
+ end
+ end
+
+ namespace "samples" do
+ task :build do
+ # Build the sample programs
+ end
+ end
+
+ task :build => ["main:build", "samples:build"]
+
+Referencing a task in a separate namespace can be achieved by
+prefixing the task name with the namespace and a colon
+(e.g. "main:build" refers to the :build task in the +main+ namespace).
+Nested namespaces are supported, so
+
+Note that the name given in the +task+ command is always the unadorned
+task name without any namespace prefixes. The +task+ command always
+defines a task in the current namespace.
+
+=== FileTasks
+
+File task names are not scoped by the namespace command. Since the
+name of a file task is the name of an actual file in the file system,
+it makes little sense to include file task names in name space.
+Directory tasks (created by the +directory+ command) are a type of
+file task and are also not affected by namespaces.
+
+=== Name Resolution
+
+When looking up a task name, rake will start with the current
+namespace and attempt to find the name there. If it fails to find a
+name in the current namespace, it will search the parent namespaces
+until a match is found (or an error occurs if there is no match).
+
+The "rake" namespace is a special implicit namespace that refers to
+the toplevel names.
+
+If a task name begins with a "^" character, the name resolution will
+start in the parent namespace. Multiple "^" characters are allowed.
+
+Here is an example file with multiple :run tasks and how various names
+resolve in different locations.
+
+ task :run
+
+ namespace "one" do
+ task :run
+
+ namespace "two" do
+ task :run
+
+ # :run => "one:two:run"
+ # "two:run" => "one:two:run"
+ # "one:two:run" => "one:two:run"
+ # "one:run" => "one:run"
+ # "^run" => "one:run"
+ # "^^run" => "rake:run" (the top level task)
+ # "rake:run" => "rake:run" (the top level task)
+ end
+
+ # :run => "one:run"
+ # "two:run" => "one:two:run"
+ # "^run" => "rake:run"
+ end
+
+ # :run => "rake:run"
+ # "one:run" => "one:run"
+ # "one:two:run" => "one:two:run"
+
+== FileLists
+
+FileLists are the way Rake manages lists of files. You can treat a
+FileList as an array of strings for the most part, but FileLists
+support some additional operations.
+
+=== Creating a FileList
+
+Creating a file list is easy. Just give it the list of file names:
+
+ fl = FileList['file1.rb', file2.rb']
+
+Or give it a glob pattern:
+
+ fl = FileList['*.rb']
+
+== Odds and Ends
+
+=== do/end versus { }
+
+Blocks may be specified with either a +do+/+end+ pair, or with curly
+braces in Ruby. We _strongly_ recommend using +do+/+end+ to specify the
+actions for tasks and rules. Because the rakefile idiom tends to
+leave off parentheses on the task/file/rule methods, unusual
+ambiguities can arise when using curly braces.
+
+For example, suppose that the method +object_files+ returns a list of
+object files in a project. Now we use +object_files+ as the
+prerequisites in a rule specified with actions in curly braces.
+
+ # DON'T DO THIS!
+ file "prog" => object_files {
+ # Actions are expected here (but it doesn't work)!
+ }
+
+Because curly braces have a higher precedence than +do+/+end+, the
+block is associated with the +object_files+ method rather than the
++file+ method.
+
+This is the proper way to specify the task ...
+
+ # THIS IS FINE
+ file "prog" => object_files do
+ # Actions go here
+ end
+
+----
+
+== See
+
+* README.rdoc -- Main documentation for Rake.