Kernel#capture replaced by version which can catch output from subprocesses

activesupport/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
+*   Kernel#capture can catch output from subprocesses *Dmitry Vorotilin*
 
 *   Make callstack attribute optional in
     ActiveSupport::Deprecation::Reporting methods `warn` and `deprecation_warning`

activesupport/lib/active_support/core_ext/kernel/reporting.rb

 require 'rbconfig'
+require 'tempfile'
 
 module Kernel
   # Sets $VERBOSE to nil for the duration of the block and back to its original
@@ -66,19 +67,33 @@ def suppress(*exception_classes)
 
   # Captures the given stream and returns it:
   #
-  #   stream = capture(:stdout) { puts 'Cool' }
-  #   stream # => "Cool\n"
+  #   stream = capture(:stdout) { puts 'notice' }
+  #   stream # => "notice\n"
+  #
+  #   stream = capture(:stderr) { warn 'error' }
+  #   stream # => "error\n"
+  #
+  # even for subprocesses:
+  #
+  #   stream = capture(:stdout) { system('echo notice') }
+  #   stream # => "notice\n"
+  #
+  #   stream = capture(:stderr) { system('echo error 1>&2') }
+  #   stream # => "error\n"
   def capture(stream)
-    begin
-      stream = stream.to_s
-      eval "$#{stream} = StringIO.new"
-      yield
-      result = eval("$#{stream}").string
-    ensure
-      eval("$#{stream} = #{stream.upcase}")
-    end
+    stream = stream.to_s
+    captured_stream = Tempfile.new(stream)
+    stream_io = eval("$#{stream}")
+    origin_stream = stream_io.dup
+    stream_io.reopen(captured_stream)
+
+    yield
 
-    result
+    stream_io.rewind
+    return captured_stream.read
+  ensure
+    captured_stream.unlink
+    stream_io.reopen(origin_stream)
   end
   alias :silence :capture
 

activesupport/test/core_ext/kernel_test.rb

@@ -51,6 +51,8 @@ class << o; @x = 1; end
   def test_capture
     assert_equal 'STDERR', capture(:stderr) { $stderr.print 'STDERR' }
     assert_equal 'STDOUT', capture(:stdout) { print 'STDOUT' }
+    assert_equal "STDERR\n", capture(:stderr) { system('echo STDERR 1>&2') }
+    assert_equal "STDOUT\n", capture(:stdout) { system('echo STDOUT') }
   end
 end