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.