Added a command builder to the list of default builders

README.md

@@ -210,6 +210,7 @@ end
 
 Rscons ships with a number of builders:
 
+* Command, which executes a user-defined command to produce the target
 * CFile, which builds a C or C++ source file from a lex or yacc input file
 * Disassemble, which disassembles an object file to a disassembly listing
 * Library, which collects object files into a static library archive file
@@ -220,6 +221,18 @@ Rscons ships with a number of builders:
 If you want to create an Environment that does not contain any builders,
 you can use the `exclude_builders` key to the Environment constructor.
 
+#### Command
+
+```ruby
+env.Command(target, sources, 'CMD' => command)
+# Example
+env.Command("docs.html", "docs.md",
+    CMD => ['pandoc', '-fmarkdown', '-thtml', '-o${_TARGET}', '${_SOURCES}'])
+```
+
+The command builder executes a user-defined command in order to produce the
+desired target file based on the provided source files.
+
 #### CFile
 
 ```ruby

lib/rscons.rb

@@ -6,6 +6,7 @@ require_relative "rscons/varset"
 require_relative "rscons/version"
 
 # default builders
+require_relative "rscons/builders/command"
 require_relative "rscons/builders/cfile"
 require_relative "rscons/builders/disassemble"
 require_relative "rscons/builders/library"
@@ -18,6 +19,7 @@ module Rscons
   # Names of the default builders which will be added to all newly created
   # {Environment} objects.
   DEFAULT_BUILDERS = [
+    :Command,
     :CFile,
     :Disassemble,
     :Library,

lib/rscons/builders/command.rb

@@ -0,0 +1,30 @@
+module Rscons
+  module Builders
+    # Execute a command that will produce the given target based on the given
+    # sources.
+    #
+    # Example::
+    #   env.Command("docs.html", "docs.md",
+    #       CMD => ['pandoc', '-fmarkdown', '-thtml', '-o${_TARGET}', '${_SOURCES}'])
+    class Command < Builder
+      # Run the builder to produce a build target.
+      #
+      # @param target [String] Target file name.
+      # @param sources [Array<String>] Source file name(s).
+      # @param cache [Cache] The Cache object.
+      # @param env [Environment] The Environment executing the builder.
+      # @param vars [Hash,VarSet] Extra construction variables.
+      #
+      # @return [String,false]
+      #   Name of the target file on success or false on failure.
+      def run(target, sources, cache, env, vars)
+        vars = vars.merge({
+          "_TARGET" => target,
+          "_SOURCES" => sources,
+        })
+        command = env.build_command("${CMD}", vars)
+        standard_build("CMD #{target}", target, command, sources, env, cache)
+      end
+    end
+  end
+end

spec/rscons/builders/command_spec.rb

@@ -0,0 +1,16 @@
+module Rscons
+  module Builders
+    describe Command do
+      let(:command) { ['pandoc', '-fmarkdown', '-thtml', '-o${_TARGET}', '${_SOURCES}'] }
+      let(:env) {Environment.new}
+      subject {Command.new}
+
+
+      it "invokes the command to build the target" do
+        expected_cmd = ['pandoc', '-fmarkdown', '-thtml', '-ofoo.html', 'foo.md']
+        expect(subject).to receive(:standard_build).with("CMD foo.html", "foo.html", expected_cmd, ["foo.md"], env, :cache)
+        subject.run("foo.html", ["foo.md"], :cache, env, {'CMD' => command})
+      end
+    end
+  end
+end