diff --git a/src/Print.hs b/src/Print.hs
index 1f899d3..286c1e7 100644
--- a/src/Print.hs
+++ b/src/Print.hs
@@ -8,53 +8,69 @@
 --   may lose other data
 
 module Print
+  ( printShellTest
+  , packResult
+  )
 where
 
-import Safe (lastMay)
 import Import
 import Types
 
--- | Print a shell test. See CLI documentation for details.
+-- | Print a shell test considering the @--actual=mode@ option. See CLI
+-- documentation for details on.
 -- For v3 (the preferred, lightweight format), avoid printing most unnecessary things
 -- (stdout delimiter, 0 exit status value).
 printShellTest
   :: String               -- ^ Shelltest format. Value of option @--print[=FORMAT]@.
+  -> Maybe String         -- ^ Value of option @--actual[=MODE]@. @Nothing@ if option is not given.
   -> ShellTest            -- ^ Test to print
+  -> Either String String -- ^ Actual stdout, non-matching or matching
+  -> Either String String -- ^ Actual stderr, non-matching or matching
+  -> Either Int Int       -- ^ Actual exit status, non-matching or matching
   -> IO ()
-printShellTest format ShellTest{command=c,stdin=i,comments=comments,trailingComments=trailingComments,
+printShellTest format actualMode ShellTest{command=c,stdin=i,comments=comments,trailingComments=trailingComments,
                stdoutExpected=o_expected,stderrExpected=e_expected,exitCodeExpected=x_expected}
-               = do
+               o_actual e_actual x_actual = do
+  (o,e,x) <- computeResults actualMode
   case format of
     "v1" -> do
       printComments comments
       printCommand "" c
       printStdin "<<<" i
-      printStdouterr False ">>>" o_expected
-      printStdouterr False ">>>2" e_expected
-      printExitStatus True True ">>>=" x_expected
+      printStdouterr ">>>" $ justMatcherOutErr o
+      printStdouterr ">>>2" $ justMatcherOutErr e
+      printExitStatus True ">>>=" x
       printComments trailingComments
     "v2" -> do
       printComments comments
       printStdin "<<<" i
       printCommand "$$$ " c
-      printStdouterr True ">>>" o_expected
-      printStdouterr True ">>>2" e_expected
-      printExitStatus trailingblanklines True ">>>=" x_expected
+      printStdouterr ">>>" $ justMatcherOutErr o
+      printStdouterr ">>>2" $ justMatcherOutErr e
+      printExitStatus False ">>>=" x
       printComments trailingComments
     "v3" -> do
       printComments comments
       printStdin "<" i
       printCommand "$ "  c
-      printStdouterr True ">" o_expected
-      printStdouterr True ">2" e_expected
-      printExitStatus trailingblanklines False ">=" x_expected
+      printStdouterr ">" $ justMatcherOutErr o
+      printStdouterr ">2" $ justMatcherOutErr e
+      printExitStatus False ">=" x
       printComments trailingComments
     _ -> fail $ "Unsupported --print format: " ++ format
   where
-    trailingblanklines = case (o_expected, e_expected) of
-      (Just (Lines _ o), Just (Lines _ e)) -> hasblanks $ if null e then o else e
-      _ -> False
-      where hasblanks s = maybe False null $ lastMay $ lines s
+    computeResults :: Maybe String -> IO (Maybe Matcher, Maybe Matcher, Matcher)
+    computeResults Nothing = return (o_expected, e_expected, x_expected)
+    computeResults (Just mode)
+     | mode `isPrefixOf` "all" = return
+         (Just $ Lines 0 $ fromEither o_actual
+         ,Just $ Lines 0 $ fromEither e_actual
+         ,Numeric $ show $ fromEither x_actual)
+     | mode `isPrefixOf` "update" = return
+         (either (Just . Lines 0) (const o_expected) o_actual
+         ,either (Just . Lines 0) (const e_expected) e_actual
+         ,either (Numeric . show) (const x_expected) x_actual)
+     | otherwise = fail "Unsupported argument for --actual option. Allowed: all, update, or a prefix thereof."
 
 printComments :: [String] -> IO ()
 printComments = mapM_ putStrLn
@@ -68,23 +84,32 @@ printCommand :: String -> TestCommand -> IO ()
 printCommand prefix (ReplaceableCommand s) = printf "%s%s\n" prefix s
 printCommand prefix (FixedCommand s)       = printf "%s %s\n" prefix s
 
--- Print an expected stdout or stderr test, prefixed with the given delimiter.
--- If no expected value is specified, print nothing if first argument is true
--- (for format 1, which ignores unspecified out/err), otherwise print a dummy test.
-printStdouterr :: Bool -> String -> Maybe Matcher -> IO ()
-printStdouterr alwaystest prefix Nothing                 = when alwaystest $ printf "%s //\n" prefix
-printStdouterr _ _ (Just (Lines _ ""))                   = return ()
-printStdouterr _ _ (Just (Numeric _))                    = fail "FATAL: Cannot handle Matcher (Numeric) for stdout/stderr."
-printStdouterr _ _ (Just (NegativeNumeric _))            = fail "FATAL: Cannot handle Matcher (NegativeNumeric) for stdout/stderr."
-printStdouterr _ prefix (Just (Lines _ s)) | prefix==">" = printf "%s" s  -- omit v3's > delimiter, really no need for it
-printStdouterr _ prefix (Just (Lines _ s))               = printf "%s\n%s" prefix s
-printStdouterr _ prefix (Just regex)                     = printf "%s %s\n" prefix (show regex)
+printStdouterr :: String -> Maybe Matcher -> IO ()
+printStdouterr _ Nothing                    = return ()
+printStdouterr _ (Just (Lines _ ""))        = return ()
+printStdouterr _ (Just (Numeric _))         = fail "FATAL: Cannot handle Matcher (Numeric) for stdout/stderr."
+printStdouterr _ (Just (NegativeNumeric _)) = fail "FATAL: Cannot handle Matcher (NegativeNumeric) for stdout/stderr."
+printStdouterr ">" (Just (Lines _ s))       = printf "%s" s -- omit the optional ">" in format v3
+printStdouterr prefix (Just (Lines _ s))    = printf "%s\n%s" prefix s
+printStdouterr prefix (Just regex)          = printf "%s %s\n" prefix (show regex)
+
 
 -- | Print an expected exit status clause, prefixed with the given delimiter.
--- If zero is expected:
---  if the first argument is not true, nothing will be printed;
---  otherwise if the second argument is not true, only the delimiter will be printed.
-printExitStatus :: Bool -> Bool ->  String -> Matcher ->      IO ()
-printExitStatus    _       _        _         (Lines _ _)   = fail "FATAL: Cannot handle Matcher (Lines) for exit status."
-printExitStatus    always  showzero prefix    (Numeric "0") = when always $ printf "%s %s\n" prefix (if showzero then "0" else "")
-printExitStatus    _       _        prefix    s             = printf "%s %s\n" prefix (show s)
+-- First arg says 'alwaysPrintEvenIfZero'.
+printExitStatus :: Bool -> String -> Matcher -> IO ()
+printExitStatus _ _ (Lines _ _) = fail "FATAL: Cannot handle Matcher (Lines) for exit status."
+printExitStatus False _     (Numeric "0") = return ()
+printExitStatus True prefix (Numeric "0") = printf "%s 0\n" prefix
+printExitStatus _ prefix s = printf "%s %s\n" prefix (show s)
+
+-- | Wrap result @a@ into 'Either' depending on wether it matches the expected result.
+packResult :: Bool -> a -> Either a a
+packResult True = Right
+packResult False = Left
+
+fromEither :: Either a a -> a
+fromEither = either id id
+
+-- | Return the default 'Matcher' for 'Nothing'.
+justMatcherOutErr :: Maybe Matcher -> Maybe Matcher
+justMatcherOutErr = Just . fromMaybe (Lines 0 "")
diff --git a/src/shelltest.hs b/src/shelltest.hs
index 825d50c..b9e6ad7 100644
--- a/src/shelltest.hs
+++ b/src/shelltest.hs
@@ -31,7 +31,7 @@ import Import
 import Utils
 import Types
 import Parse
-import Print
+import Print (printShellTest, packResult)
 import Preprocessor
 
 
@@ -73,6 +73,7 @@ data Args = Args {
     ,testpaths   :: [FilePath]
     ,print_      :: Maybe String
     ,hspec_      :: Bool
+    ,actual      :: Maybe String
     } deriving (Show, Data, Typeable)
 
 argdefs = Args {
@@ -98,6 +99,7 @@ argdefs = Args {
     ,testpaths   = def     &= args &= typ "TESTFILES|TESTDIRS"
     ,print_      = def     &= typ "FORMAT" &= opt "v3" &= groupname "Print test file" &= help "Print test files in specified format (default: v3)."
     ,hspec_      = def     &= name"hspec" &= help "Use hspec to run tests."
+    ,actual      = def     &= typ "MODE"   &= opt "all" &= help "Combined with --print, print test files with actual results (stdout, stderr, exit status). This can be used to generate or update tests. Mode 'all' prints all actual results (default). Mode 'update' prints actual results only for non-matching results, i.e. regular expressions in tests are retained."
     }
     &= helpArg [explicit, name "help", name "h"]
     &= program progname
@@ -178,6 +180,8 @@ checkArgs :: Args -> IO Args
 checkArgs args = do
   when (null $ testpaths args) $
        warn $ printf "Please specify at least one test file or directory, eg: %s tests" progname
+  when (isJust (actual args) && isNothing (print_ args)) $
+       warn "Option --actual can only be used with --print."
   return args
 
 -- running tests
@@ -209,7 +213,7 @@ prepareShellTest args st@ShellTest{testname=n,command=c,stdin=i,stdoutExpected=o
   let errorMatch = maybe True (e_actual `matches`) e_expected
   let exitCodeMatch = show x_actual `matches` x_expected
   case print_ args of
-    Just format -> printShellTest format st
+    Just format -> printShellTest format (actual args) st (packResult outputMatch o_actual) (packResult errorMatch e_actual) (packResult exitCodeMatch x_actual)
     Nothing -> if (x_actual == 127) -- catch bad executable - should work on posix systems at least
            then ioError $ userError $ unwords $ filter (not . null) [e_actual, printf "Command: '%s' Exit code: %i" cmd x_actual] -- XXX still a test failure; should be an error
            else assertString $ concat $ filter (not . null) [
diff --git a/tests/print/print-actual-no-results.test.txt b/tests/print/print-actual-no-results.test.txt
new file mode 100644
index 0000000..5551b1d
--- /dev/null
+++ b/tests/print/print-actual-no-results.test.txt
@@ -0,0 +1,5 @@
+$  echo foo
+
+$  cat --invalid-option
+
+$  false
diff --git a/tests/print/print-actual.test b/tests/print/print-actual.test
new file mode 100644
index 0000000..8301c02
--- /dev/null
+++ b/tests/print/print-actual.test
@@ -0,0 +1,11 @@
+$  echo foo
+foo
+
+$  cat --invalid-option
+>2
+cat: unrecognized option '--invalid-option'
+Try 'cat --help' for more information.
+>= 1
+
+$  false
+>= 1
diff --git a/tests/print/print-format3.test b/tests/print/print-format3.test
index cd89065..3e4342d 100644
--- a/tests/print/print-format3.test
+++ b/tests/print/print-format3.test
@@ -2,3 +2,9 @@
 $ shelltest --print=v3 tests/format3/ideal.test | diff -u - tests/format3/ideal.test
 
 $ shelltest --print tests/format3/ideal.test | diff -u - tests/format3/ideal.test
+
+$ shelltest --print --actual=update tests/format3/ideal.test | diff -u - tests/format3/ideal.test
+
+$ shelltest --print --actual=all tests/print/print-actual.test | diff -u - tests/print/print-actual.test
+
+$  cp tests/print/print-actual-no-results.test.txt /tmp/print-actual-no-results.test && shelltest --print --actual=all /tmp/print-actual-no-results.test | diff -u - tests/print/print-actual.test