add Environment#shell - close #11

lib/rscons.rb

@@ -54,4 +54,33 @@ module Rscons
   def self.set_suffix(path, suffix)
     path.sub(/\.[^.]*$/, suffix)
   end
+
+  # Return the system shell and arguments for executing a shell command.
+  # @return [Array<String>] The shell and flag.
+  def self.get_system_shell
+    @@shell ||=
+      begin
+        test_shell = lambda do |*args|
+          begin
+            "success" == IO.popen([*args, "echo success"]) do |io|
+              io.read.strip
+            end
+          rescue
+            false
+          end
+        end
+        if ENV["SHELL"] and ENV["SHELL"] != "" and test_shell[ENV["SHELL"], "-c"]
+          [ENV["SHELL"], "-c"]
+        elsif Object.const_get("RUBY_PLATFORM") =~ /mingw/
+          if test_shell["sh", "-c"]
+            # Using Rscons from MSYS should use MSYS's shell.
+            ["sh", "-c"]
+          else
+            ["cmd", "/c"]
+          end
+        else
+          ["sh", "-c"]
+        end
+      end
+  end
 end

lib/rscons/environment.rb

@@ -349,6 +349,35 @@ module Rscons
       path.sub(%r{^\^(?=[\\/])}, @build_root)
     end
 
+    # Execute a command using the system shell.
+    #
+    # The shell is automatically determined but can be overridden by the SHELL
+    # construction variable. If the SHELL construction variable is specified,
+    # the flag to pass to the shell is automatically dtermined but can be
+    # overridden by the SHELLFLAG construction variable.
+    #
+    # @param command [String] Command to execute.
+    #
+    # @return [String] The command's standard output.
+    def shell(command)
+      shell_cmd =
+        if self["SHELL"]
+          flag = self["SHELLFLAG"] || begin
+            if self["SHELL"] == "cmd"
+              "/c"
+            else
+              "-c"
+            end
+          end
+          [self["SHELL"], flag]
+        else
+          Rscons.get_system_shell
+        end
+      IO.popen([*shell_cmd, command]) do |io|
+        io.read
+      end
+    end
+
     private
 
     # Expand target and source paths before invoking builders.

spec/rscons/environment_spec.rb

@@ -360,6 +360,25 @@ module Rscons
       end
     end
 
+    describe "#shell" do
+      it "executes the given shell command and returns the results" do
+        env = Environment.new
+        expect(env.shell("echo hello").strip).to eq("hello")
+      end
+      it "determines shell flag to be /c when SHELL is specified as 'cmd'" do
+        env = Environment.new
+        env["SHELL"] = "cmd"
+        IO.should_receive(:popen).with(["cmd", "/c", "my_cmd"])
+        env.shell("my_cmd")
+      end
+      it "determines shell flag to be -c when SHELL is specified as something else" do
+        env = Environment.new
+        env["SHELL"] = "my_shell"
+        IO.should_receive(:popen).with(["my_shell", "-c", "my_cmd"])
+        env.shell("my_cmd")
+      end
+    end
+
     describe ".parse_makefile_deps" do
       it 'handles dependencies on one line' do
         File.should_receive(:read).with('makefile').and_return(<<EOS)

spec/rscons_spec.rb

@@ -23,4 +23,47 @@ describe Rscons do
       Rscons.clean
     end
   end
+
+  describe ".get_system_shell" do
+    before(:each) do
+      Rscons.class_variable_set(:@@shell, nil)
+    end
+
+    after(:each) do
+      Rscons.class_variable_set(:@@shell, nil)
+    end
+
+    it "uses the SHELL environment variable if it tests successfully" do
+      my_ENV = {"SHELL" => "my_shell"}
+      ENV.stub(:[]) {|*args| my_ENV[*args]}
+      io = StringIO.new("success\n")
+      IO.should_receive(:popen).with(["my_shell", "-c", "echo success"]).and_yield(io)
+      expect(Rscons.get_system_shell).to eq(["my_shell", "-c"])
+    end
+
+    it "uses sh -c on a mingw platform if it tests successfully" do
+      my_ENV = {"SHELL" => nil}
+      ENV.stub(:[]) {|*args| my_ENV[*args]}
+      io = StringIO.new("success\n")
+      IO.should_receive(:popen).with(["sh", "-c", "echo success"]).and_yield(io)
+      Object.should_receive(:const_get).with("RUBY_PLATFORM").and_return("x86-mingw")
+      expect(Rscons.get_system_shell).to eq(["sh", "-c"])
+    end
+
+    it "uses cmd /c on a mingw platform if sh -c does not test successfully" do
+      my_ENV = {"SHELL" => nil}
+      ENV.stub(:[]) {|*args| my_ENV[*args]}
+      io = StringIO.new("success\n")
+      IO.should_receive(:popen).with(["sh", "-c", "echo success"]).and_raise "ENOENT"
+      Object.should_receive(:const_get).with("RUBY_PLATFORM").and_return("x86-mingw")
+      expect(Rscons.get_system_shell).to eq(["cmd", "/c"])
+    end
+
+    it "uses sh -c on a non-mingw platform if SHELL is not specified" do
+      my_ENV = {"SHELL" => nil}
+      ENV.stub(:[]) {|*args| my_ENV[*args]}
+      Object.should_receive(:const_get).with("RUBY_PLATFORM").and_return("x86-linux")
+      expect(Rscons.get_system_shell).to eq(["sh", "-c"])
+    end
+  end
 end