On 1.9, Kernel.system returns nil if exec fails

kernel/common/process.rb

@@ -710,29 +710,6 @@ def fork(&block)
   end
   module_function :fork
 
-  def system(prog, *args)
-    pid = Process.fork
-    if pid
-      Process.waitpid(pid)
-      $?.exitstatus == 0
-    else
-      begin
-        Kernel.exec(prog, *args)
-      rescue Exception => e
-        if $DEBUG
-          e.render("Unable to execute subprogram", STDERR)
-        end
-        exit! 1
-      end
-
-      if $DEBUG
-        STDERR.puts "Unable to execute subprogram - exec silently returned"
-      end
-      exit! 1
-    end
-  end
-  module_function :system
-
   def `(str) #`
     str = StringValue(str) unless str.kind_of?(String)
     pid, output = Process.replace(str)

kernel/common/process18.rb

@@ -26,3 +26,28 @@ def self.exec(cmd, *args)
     end
   end
 end
+
+module Kernel
+  def system(prog, *args)
+    pid = Process.fork
+    if pid
+      Process.waitpid(pid)
+      $?.exitstatus == 0
+    else
+      begin
+        Kernel.exec(prog, *args)
+      rescue Exception => e
+        if $DEBUG
+          e.render("Unable to execute subprogram", STDERR)
+        end
+        exit! 1
+      end
+
+      if $DEBUG
+        STDERR.puts "Unable to execute subprogram - exec silently returned"
+      end
+      exit! 1
+    end
+  end
+  module_function :system
+end

kernel/common/process19.rb

@@ -69,3 +69,30 @@ def self.exec(environment_or_cmd, *args)
     end
   end
 end
+
+module Kernel
+  def system(prog, *args)
+    IO.pipe do |read, write|
+      pid = Process.fork do
+        read.close
+
+        begin
+          Kernel.exec(prog, *args)
+        ensure
+          write.write false
+          exit! 1
+        end
+      end
+
+      write.close
+      Process.waitpid(pid)
+
+      if read.eof?
+        $?.exitstatus == 0
+      else
+        nil
+      end
+    end
+  end
+  module_function :system
+end