Index: llvm/utils/lit/lit/TestRunner.py
===================================================================
--- llvm/utils/lit/lit/TestRunner.py
+++ llvm/utils/lit/lit/TestRunner.py
@@ -1,5 +1,4 @@
 from __future__ import absolute_import
-import difflib
 import errno
 import functools
 import io
@@ -360,218 +359,6 @@
                 exitCode = 1
     return ShellCommandResult(cmd, "", stderr.getvalue(), exitCode, False)
 
-def executeBuiltinDiff(cmd, cmd_shenv):
-    """executeBuiltinDiff - Compare files line by line."""
-    args = expand_glob_expressions(cmd.args, cmd_shenv.cwd)[1:]
-    try:
-        opts, args = getopt.gnu_getopt(args, "wbur", ["strip-trailing-cr"])
-    except getopt.GetoptError as err:
-        raise InternalShellError(cmd, "Unsupported: 'diff':  %s" % str(err))
-
-    filelines, filepaths, dir_trees = ([] for i in range(3))
-    ignore_all_space = False
-    ignore_space_change = False
-    unified_diff = False
-    recursive_diff = False
-    strip_trailing_cr = False
-    for o, a in opts:
-        if o == "-w":
-            ignore_all_space = True
-        elif o == "-b":
-            ignore_space_change = True
-        elif o == "-u":
-            unified_diff = True
-        elif o == "-r":
-            recursive_diff = True
-        elif o == "--strip-trailing-cr":
-            strip_trailing_cr = True
-        else:
-            assert False, "unhandled option"
-
-    if len(args) != 2:
-        raise InternalShellError(cmd, "Error:  missing or extra operand")
-
-    def getDirTree(path, basedir=""):
-        # Tree is a tuple of form (dirname, child_trees).
-        # An empty dir has child_trees = [], a file has child_trees = None.
-        child_trees = []
-        for dirname, child_dirs, files in os.walk(os.path.join(basedir, path)):
-            for child_dir in child_dirs:
-                child_trees.append(getDirTree(child_dir, dirname))
-            for filename in files:
-                child_trees.append((filename, None))
-            return path, sorted(child_trees)
-
-    def compareTwoFiles(filepaths):
-        compare_bytes = False
-        encoding = None
-        filelines = []
-        for file in filepaths:
-            try:
-                with open(file, 'r') as f:
-                    filelines.append(f.readlines())
-            except UnicodeDecodeError:
-                try:
-                    with io.open(file, 'r', encoding="utf-8") as f:
-                        filelines.append(f.readlines())
-                    encoding = "utf-8"
-                except:
-                    compare_bytes = True
-
-        if compare_bytes:
-            return compareTwoBinaryFiles(filepaths)
-        else:
-            return compareTwoTextFiles(filepaths, encoding)
-
-    def compareTwoBinaryFiles(filepaths):
-        filelines = []
-        for file in filepaths:
-            with open(file, 'rb') as f:
-                filelines.append(f.readlines())
-
-        exitCode = 0
-        if hasattr(difflib, 'diff_bytes'):
-            # python 3.5 or newer
-            diffs = difflib.diff_bytes(difflib.unified_diff, filelines[0], filelines[1], filepaths[0].encode(), filepaths[1].encode())
-            diffs = [diff.decode() for diff in diffs]
-        else:
-            # python 2.7
-            func = difflib.unified_diff if unified_diff else difflib.context_diff
-            diffs = func(filelines[0], filelines[1], filepaths[0], filepaths[1])
-
-        for diff in diffs:
-            stdout.write(diff)
-            exitCode = 1
-        return exitCode
-
-    def compareTwoTextFiles(filepaths, encoding):
-        filelines = []
-        for file in filepaths:
-            if encoding is None:
-                with open(file, 'r') as f:
-                    filelines.append(f.readlines())
-            else:
-                with io.open(file, 'r', encoding=encoding) as f:
-                    filelines.append(f.readlines())
-
-        exitCode = 0
-        def compose2(f, g):
-            return lambda x: f(g(x))
-
-        f = lambda x: x
-        if strip_trailing_cr:
-            f = compose2(lambda line: line.rstrip('\r'), f)
-        if ignore_all_space or ignore_space_change:
-            ignoreSpace = lambda line, separator: separator.join(line.split())
-            ignoreAllSpaceOrSpaceChange = functools.partial(ignoreSpace, separator='' if ignore_all_space else ' ')
-            f = compose2(ignoreAllSpaceOrSpaceChange, f)
-
-        for idx, lines in enumerate(filelines):
-            filelines[idx]= [f(line) for line in lines]
-
-        func = difflib.unified_diff if unified_diff else difflib.context_diff
-        for diff in func(filelines[0], filelines[1], filepaths[0], filepaths[1]):
-            stdout.write(diff)
-            exitCode = 1
-        return exitCode
-
-    def printDirVsFile(dir_path, file_path):
-        if os.path.getsize(file_path):
-            msg = "File %s is a directory while file %s is a regular file"
-        else:
-            msg = "File %s is a directory while file %s is a regular empty file"
-        stdout.write(msg % (dir_path, file_path) + "\n")
-
-    def printFileVsDir(file_path, dir_path):
-        if os.path.getsize(file_path):
-            msg = "File %s is a regular file while file %s is a directory"
-        else:
-            msg = "File %s is a regular empty file while file %s is a directory"
-        stdout.write(msg % (file_path, dir_path) + "\n")
-
-    def printOnlyIn(basedir, path, name):
-        stdout.write("Only in %s: %s\n" % (os.path.join(basedir, path), name))
-
-    def compareDirTrees(dir_trees, base_paths=["", ""]):
-        # Dirnames of the trees are not checked, it's caller's responsibility,
-        # as top-level dirnames are always different. Base paths are important
-        # for doing os.walk, but we don't put it into tree's dirname in order
-        # to speed up string comparison below and while sorting in getDirTree.
-        left_tree, right_tree = dir_trees[0], dir_trees[1]
-        left_base, right_base = base_paths[0], base_paths[1]
-
-        # Compare two files or report file vs. directory mismatch.
-        if left_tree[1] is None and right_tree[1] is None:
-            return compareTwoFiles([os.path.join(left_base, left_tree[0]),
-                                    os.path.join(right_base, right_tree[0])])
-
-        if left_tree[1] is None and right_tree[1] is not None:
-            printFileVsDir(os.path.join(left_base, left_tree[0]),
-                           os.path.join(right_base, right_tree[0]))
-            return 1
-
-        if left_tree[1] is not None and right_tree[1] is None:
-            printDirVsFile(os.path.join(left_base, left_tree[0]),
-                           os.path.join(right_base, right_tree[0]))
-            return 1
-
-        # Compare two directories via recursive use of compareDirTrees.
-        exitCode = 0
-        left_names = [node[0] for node in left_tree[1]]
-        right_names = [node[0] for node in right_tree[1]]
-        l, r = 0, 0
-        while l < len(left_names) and r < len(right_names):
-            # Names are sorted in getDirTree, rely on that order.
-            if left_names[l] < right_names[r]:
-                exitCode = 1
-                printOnlyIn(left_base, left_tree[0], left_names[l])
-                l += 1
-            elif left_names[l] > right_names[r]:
-                exitCode = 1
-                printOnlyIn(right_base, right_tree[0], right_names[r])
-                r += 1
-            else:
-                exitCode |= compareDirTrees([left_tree[1][l], right_tree[1][r]],
-                                            [os.path.join(left_base, left_tree[0]),
-                                            os.path.join(right_base, right_tree[0])])
-                l += 1
-                r += 1
-
-        # At least one of the trees has ended. Report names from the other tree.
-        while l < len(left_names):
-            exitCode = 1
-            printOnlyIn(left_base, left_tree[0], left_names[l])
-            l += 1
-        while r < len(right_names):
-            exitCode = 1
-            printOnlyIn(right_base, right_tree[0], right_names[r])
-            r += 1
-        return exitCode
-
-    stderr = StringIO()
-    stdout = StringIO()
-    exitCode = 0
-    try:
-        for file in args:
-            if not os.path.isabs(file):
-                file = os.path.realpath(os.path.join(cmd_shenv.cwd, file))
-    
-            if recursive_diff:
-                dir_trees.append(getDirTree(file))
-            else:
-                filepaths.append(file)
-
-        if not recursive_diff:
-            exitCode = compareTwoFiles(filepaths)
-        else:
-            exitCode = compareDirTrees(dir_trees)
-
-    except IOError as err:
-        stderr.write("Error: 'diff' command failed, %s\n" % str(err))
-        exitCode = 1
-
-    return ShellCommandResult(cmd, stdout.getvalue(), stderr.getvalue(), exitCode, False)
-
 def executeBuiltinRm(cmd, cmd_shenv):
     """executeBuiltinRm - Removes (deletes) files or directories."""
     args = expand_glob_expressions(cmd.args, cmd_shenv.cwd)[1:]
@@ -837,14 +624,6 @@
         results.append(cmdResult)
         return cmdResult.exitCode
 
-    if cmd.commands[0].args[0] == 'diff':
-        if len(cmd.commands) != 1:
-            raise InternalShellError(cmd.commands[0], "Unsupported: 'diff' "
-                                     "cannot be part of a pipeline")
-        cmdResult = executeBuiltinDiff(cmd.commands[0], shenv)
-        results.append(cmdResult)
-        return cmdResult.exitCode
-
     if cmd.commands[0].args[0] == 'rm':
         if len(cmd.commands) != 1:
             raise InternalShellError(cmd.commands[0], "Unsupported: 'rm' "
@@ -865,7 +644,7 @@
     stderrTempFiles = []
     opened_files = []
     named_temp_files = []
-    builtin_commands = set(['cat'])
+    builtin_commands = set(['cat', 'diff'])
     builtin_commands_dir = os.path.join(os.path.dirname(os.path.abspath(__file__)), "builtin_commands")
     # To avoid deadlock, we use a single stderr stream for piped
     # output. This is null until we have seen some output using
Index: llvm/utils/lit/lit/builtin_commands/diff.py
===================================================================
--- /dev/null
+++ llvm/utils/lit/lit/builtin_commands/diff.py
@@ -0,0 +1,246 @@
+import difflib
+import getopt
+import os
+import sys
+
+class DiffFlags():
+    def __init__(self):
+        self.ignore_all_space = False
+        self.ignore_space_change = False
+        self.unified_diff = False
+        self.recursive_diff = False
+        self.strip_trailing_cr = False
+
+def getDirTree(path, basedir=""):
+    # Tree is a tuple of form (dirname, child_trees).
+    # An empty dir has child_trees = [], a file has child_trees = None.
+    child_trees = []
+    for dirname, child_dirs, files in os.walk(os.path.join(basedir, path)):
+        for child_dir in child_dirs:
+            child_trees.append(getDirTree(child_dir, dirname))
+        for filename in files:
+            child_trees.append((filename, None))
+        return path, sorted(child_trees)
+
+def compareTwoFiles(flags, filepaths):
+    # FIXME: How can we restart stdin if the encoding is wrong?  How can we
+    # read stdin with a different encoding or in binary mode in a way that's
+    # compatible with python 2 and 3?
+    compare_bytes = False
+    encoding = None
+    filelines = []
+    has_stdin = False
+    for file in filepaths:
+        if file == "-":
+            has_stdin = True
+            continue
+        try:
+            with open(file, 'r') as f:
+                filelines.append(f.readlines())
+        except UnicodeDecodeError:
+            try:
+                with io.open(file, 'r', encoding="utf-8") as f:
+                    filelines.append(f.readlines())
+                encoding = "utf-8"
+            except:
+                compare_bytes = True
+
+    if has_stdin and encoding:
+        sys.stderr.write("Unsupported: cannot compare '-' with encoding {}"
+                         .format(encoding))
+        sys.exit(1)
+
+    if compare_bytes:
+        if has_stdin:
+            sys.stderr.write("Unsupported: cannot compare '-' as binary")
+            sys.exit(1)
+        return compareTwoBinaryFiles(flags, filepaths)
+    else:
+        return compareTwoTextFiles(flags, filepaths, encoding)
+
+def compareTwoBinaryFiles(flags, filepaths):
+    filelines = []
+    for file in filepaths:
+        with open(file, 'rb') as f:
+            filelines.append(f.readlines())
+
+    exitCode = 0
+    if hasattr(difflib, 'diff_bytes'):
+        # python 3.5 or newer
+        diffs = difflib.diff_bytes(difflib.unified_diff, filelines[0], filelines[1], filepaths[0].encode(), filepaths[1].encode())
+        diffs = [diff.decode() for diff in diffs]
+    else:
+        # python 2.7
+        if flags.unified_diff:
+            func = difflib.unified_diff
+        else:
+            func = difflib.context_diff
+        diffs = func(filelines[0], filelines[1], filepaths[0], filepaths[1])
+
+    for diff in diffs:
+        sys.stdout.write(diff)
+        exitCode = 1
+    return exitCode
+
+def compareTwoTextFiles(flags, filepaths, encoding):
+    filelines = []
+    for file in filepaths:
+        if file == "-":
+            filelines.append(sys.stdin.readlines())
+        elif encoding is None:
+            with open(file, 'r') as f:
+                filelines.append(f.readlines())
+        else:
+            with io.open(file, 'r', encoding=encoding) as f:
+                filelines.append(f.readlines())
+
+    exitCode = 0
+    def compose2(f, g):
+        return lambda x: f(g(x))
+
+    f = lambda x: x
+    if flags.strip_trailing_cr:
+        f = compose2(lambda line: line.rstrip('\r'), f)
+    if flags.ignore_all_space or flags.ignore_space_change:
+        ignoreSpace = lambda line, separator: separator.join(line.split())
+        ignoreAllSpaceOrSpaceChange = functools.partial(ignoreSpace, separator='' if flags.ignore_all_space else ' ')
+        f = compose2(ignoreAllSpaceOrSpaceChange, f)
+
+    for idx, lines in enumerate(filelines):
+        filelines[idx]= [f(line) for line in lines]
+
+    func = difflib.unified_diff if flags.unified_diff else difflib.context_diff
+    for diff in func(filelines[0], filelines[1], filepaths[0], filepaths[1]):
+        sys.stdout.write(diff)
+        exitCode = 1
+    return exitCode
+
+def printDirVsFile(dir_path, file_path):
+    if os.path.getsize(file_path):
+        msg = "File %s is a directory while file %s is a regular file"
+    else:
+        msg = "File %s is a directory while file %s is a regular empty file"
+    sys.stdout.write(msg % (dir_path, file_path) + "\n")
+
+def printFileVsDir(file_path, dir_path):
+    if os.path.getsize(file_path):
+        msg = "File %s is a regular file while file %s is a directory"
+    else:
+        msg = "File %s is a regular empty file while file %s is a directory"
+    sys.stdout.write(msg % (file_path, dir_path) + "\n")
+
+def printOnlyIn(basedir, path, name):
+    sys.stdout.write("Only in %s: %s\n" % (os.path.join(basedir, path), name))
+
+def compareDirTrees(flags, dir_trees, base_paths=["", ""]):
+    # Dirnames of the trees are not checked, it's caller's responsibility,
+    # as top-level dirnames are always different. Base paths are important
+    # for doing os.walk, but we don't put it into tree's dirname in order
+    # to speed up string comparison below and while sorting in getDirTree.
+    left_tree, right_tree = dir_trees[0], dir_trees[1]
+    left_base, right_base = base_paths[0], base_paths[1]
+
+    # Compare two files or report file vs. directory mismatch.
+    if left_tree[1] is None and right_tree[1] is None:
+        return compareTwoFiles(flags,
+                               [os.path.join(left_base, left_tree[0]),
+                                os.path.join(right_base, right_tree[0])])
+
+    if left_tree[1] is None and right_tree[1] is not None:
+        printFileVsDir(os.path.join(left_base, left_tree[0]),
+                       os.path.join(right_base, right_tree[0]))
+        return 1
+
+    if left_tree[1] is not None and right_tree[1] is None:
+        printDirVsFile(os.path.join(left_base, left_tree[0]),
+                       os.path.join(right_base, right_tree[0]))
+        return 1
+
+    # Compare two directories via recursive use of compareDirTrees.
+    exitCode = 0
+    left_names = [node[0] for node in left_tree[1]]
+    right_names = [node[0] for node in right_tree[1]]
+    l, r = 0, 0
+    while l < len(left_names) and r < len(right_names):
+        # Names are sorted in getDirTree, rely on that order.
+        if left_names[l] < right_names[r]:
+            exitCode = 1
+            printOnlyIn(left_base, left_tree[0], left_names[l])
+            l += 1
+        elif left_names[l] > right_names[r]:
+            exitCode = 1
+            printOnlyIn(right_base, right_tree[0], right_names[r])
+            r += 1
+        else:
+            exitCode |= compareDirTrees(flags,
+                                        [left_tree[1][l], right_tree[1][r]],
+                                        [os.path.join(left_base, left_tree[0]),
+                                        os.path.join(right_base, right_tree[0])])
+            l += 1
+            r += 1
+
+    # At least one of the trees has ended. Report names from the other tree.
+    while l < len(left_names):
+        exitCode = 1
+        printOnlyIn(left_base, left_tree[0], left_names[l])
+        l += 1
+    while r < len(right_names):
+        exitCode = 1
+        printOnlyIn(right_base, right_tree[0], right_names[r])
+        r += 1
+    return exitCode
+
+def main(argv):
+    args = argv[1:]
+    try:
+        opts, args = getopt.gnu_getopt(args, "wbur", ["strip-trailing-cr"])
+    except getopt.GetoptError as err:
+        sys.stderr.write("Unsupported: 'diff':  %s\n" % str(err))
+        sys.exit(1)
+
+    flags = DiffFlags()
+    filelines, filepaths, dir_trees = ([] for i in range(3))
+    for o, a in opts:
+        if o == "-w":
+            flags.ignore_all_space = True
+        elif o == "-b":
+            flags.ignore_space_change = True
+        elif o == "-u":
+            flags.unified_diff = True
+        elif o == "-r":
+            flags.recursive_diff = True
+        elif o == "--strip-trailing-cr":
+            flags.strip_trailing_cr = True
+        else:
+            assert False, "unhandled option"
+
+    if len(args) != 2:
+        sys.stderr.write("Error: missing or extra operand")
+        sys.exit(1)
+
+    exitCode = 0
+    try:
+        for file in args:
+            if file != "-" and not os.path.isabs(file):
+                file = os.path.realpath(os.path.join(os.getcwd(), file))
+
+            if flags.recursive_diff:
+                if file == "-":
+                    sys.stderr.write("Error: cannot recursively compare '-'")
+                dir_trees.append(getDirTree(file))
+            else:
+                filepaths.append(file)
+
+        if not flags.recursive_diff:
+            exitCode = compareTwoFiles(flags, filepaths)
+        else:
+            exitCode = compareDirTrees(flags, dir_trees)
+
+    except IOError as err:
+        sys.stderr.write("Error: 'diff' command failed, %s\n" % str(err))
+        exitCode = 1
+
+    sys.exit(exitCode)
+
+if __name__ == "__main__":
+    main(sys.argv)
Index: llvm/utils/lit/tests/Inputs/shtest-shell/diff-error-0.txt
===================================================================
--- llvm/utils/lit/tests/Inputs/shtest-shell/diff-error-0.txt
+++ /dev/null
@@ -1,3 +0,0 @@
-# Check error on a unsupported diff (cannot be part of a pipeline).
-#
-# RUN: diff diff-error-0.txt diff-error-0.txt | echo Output
Index: llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-0.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-0.txt
@@ -0,0 +1,14 @@
+# FIXME: When "not" is correctly supported on "diff", use it here so you can
+# merge diff-pipes-*.txt tests into one test.
+
+# RUN: echo foo > %t.foo
+# RUN: echo bar > %t.bar
+
+# Check output pipe.
+# RUN: diff %t.foo %t.foo | FileCheck -allow-empty -check-prefix=EMPTY %s
+# RUN: diff -u %t.foo %t.bar | FileCheck %s
+
+# CHECK:      @@
+# CHECK-NEXT: -foo
+# CHECK-NEXT: +bar
+# EMPTY-NOT: {{.}}
Index: llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-1.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-1.txt
@@ -0,0 +1,9 @@
+# FIXME: When "not" is correctly supported on "diff", use it here so you can
+# merge diff-pipes-*.txt tests into one test.
+
+# RUN: echo foo > %t.foo
+
+# Check input pipe.
+# RUN: echo foo | diff -u - %t.foo
+# RUN: echo foo | diff -u %t.foo -
+# RUN: echo bar | diff -u %t.foo -
Index: llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-2.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-2.txt
@@ -0,0 +1,7 @@
+# FIXME: When "not" is correctly supported on "diff", use it here so you can
+# merge diff-pipes-*.txt tests into one test.
+
+# RUN: echo foo > %t.foo
+
+# Check input pipe.
+# RUN: echo bar | diff -u - %t.foo
Index: llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-3.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-shell/diff-pipes-3.txt
@@ -0,0 +1,13 @@
+# FIXME: When "not" is correctly supported on "diff", use it here so you can
+# merge diff-pipes-*.txt tests into one test.
+
+# RUN: echo foo > %t.foo
+
+# Check output and input pipes at the same time.
+# RUN: echo foo | diff - %t.foo | FileCheck -allow-empty -check-prefix=EMPTY %s
+# RUN: echo bar | diff -u %t.foo - | FileCheck %s
+
+# CHECK:      @@
+# CHECK-NEXT: -foo
+# CHECK-NEXT: +bar
+# EMPTY-NOT: {{.}}
Index: llvm/utils/lit/tests/Inputs/shtest-shell/diff-r-error-7.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-shell/diff-r-error-7.txt
@@ -0,0 +1,2 @@
+# diff -r currently cannot handle stdin.
+# RUN: diff -r - %t
Index: llvm/utils/lit/tests/Inputs/shtest-shell/diff-r-error-8.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-shell/diff-r-error-8.txt
@@ -0,0 +1,2 @@
+# diff -r currently cannot handle stdin.
+# RUN: diff -r %t -
Index: llvm/utils/lit/tests/max-failures.py
===================================================================
--- llvm/utils/lit/tests/max-failures.py
+++ llvm/utils/lit/tests/max-failures.py
@@ -8,7 +8,7 @@
 #
 # END.
 
-# CHECK: Failing Tests (27)
+# CHECK: Failing Tests (32)
 # CHECK: Failing Tests (1)
 # CHECK: Failing Tests (2)
 # CHECK: error: Option '--max-failures' requires positive integer
Index: llvm/utils/lit/tests/shtest-shell.py
===================================================================
--- llvm/utils/lit/tests/shtest-shell.py
+++ llvm/utils/lit/tests/shtest-shell.py
@@ -4,7 +4,7 @@
 # FIXME: Temporarily dump test output so we can debug failing tests on
 # buildbots.
 # RUN: cat %t.out
-# RUN: FileCheck --input-file %t.out %s
+# RUN: FileCheck -dump-input=fail -vv -color --input-file %t.out %s
 #
 # END.
 
@@ -34,28 +34,20 @@
 # CHECK: error: command failed with exit status: 127
 # CHECK: ***
 
-# CHECK: FAIL: shtest-shell :: diff-error-0.txt
-# CHECK: *** TEST 'shtest-shell :: diff-error-0.txt' FAILED ***
-# CHECK: $ "diff" "diff-error-0.txt" "diff-error-0.txt"
-# CHECK: # command stderr:
-# CHECK: Unsupported: 'diff' cannot be part of a pipeline
-# CHECK: error: command failed with exit status: 127
-# CHECK: ***
-
 # CHECK: FAIL: shtest-shell :: diff-error-1.txt
 # CHECK: *** TEST 'shtest-shell :: diff-error-1.txt' FAILED ***
 # CHECK: $ "diff" "-B" "temp1.txt" "temp2.txt"
 # CHECK: # command stderr:
 # CHECK: Unsupported: 'diff': option -B not recognized
-# CHECK: error: command failed with exit status: 127
+# CHECK: error: command failed with exit status: 1
 # CHECK: ***
 
 # CHECK: FAIL: shtest-shell :: diff-error-2.txt
 # CHECK: *** TEST 'shtest-shell :: diff-error-2.txt' FAILED ***
 # CHECK: $ "diff" "temp.txt"
 # CHECK: # command stderr:
-# CHECK: Error:  missing or extra operand
-# CHECK: error: command failed with exit status: 127
+# CHECK: Error: missing or extra operand
+# CHECK: error: command failed with exit status: 1
 # CHECK: ***
 
 # CHECK: FAIL: shtest-shell :: diff-error-3.txt
@@ -82,16 +74,80 @@
 # CHECK: *** TEST 'shtest-shell :: diff-error-5.txt' FAILED ***
 # CHECK: $ "diff"
 # CHECK: # command stderr:
-# CHECK: Error:  missing or extra operand
-# CHECK: error: command failed with exit status: 127
+# CHECK: Error: missing or extra operand
+# CHECK: error: command failed with exit status: 1
 # CHECK: ***
 
 # CHECK: FAIL: shtest-shell :: diff-error-6.txt
 # CHECK: *** TEST 'shtest-shell :: diff-error-6.txt' FAILED ***
 # CHECK: $ "diff"
 # CHECK: # command stderr:
-# CHECK: Error:  missing or extra operand
-# CHECK: error: command failed with exit status: 127
+# CHECK: Error: missing or extra operand
+# CHECK: error: command failed with exit status: 1
+# CHECK: ***
+
+# CHECK: FAIL: shtest-shell :: diff-pipes-0.txt
+# CHECK: *** TEST 'shtest-shell :: diff-pipes-0.txt' FAILED ***
+# CHECK: $ "diff" "{{[^"]*}}.foo" "{{[^"]*}}.foo"
+# CHECK-NOT: note
+# CHECK-NOT: error
+# CHECK: $ "FileCheck"
+# CHECK-NOT: note
+# CHECK-NOT: error
+# CHECK: $ "diff" "-u" "{{[^"]*}}.foo" "{{[^"]*}}.bar"
+# CHECK: note: command had no output on stdout or stderr
+# CHECK: error: command failed with exit status: 1
+# CHECK: $ "FileCheck"
+# CHECK-NOT: note
+# CHECK-NOT: error
+# CHECK: ***
+
+# CHECK: FAIL: shtest-shell :: diff-pipes-1.txt
+# CHECK: *** TEST 'shtest-shell :: diff-pipes-1.txt' FAILED ***
+# CHECK: $ "echo" "foo"
+# CHECK: $ "diff" "-u" "-" "{{[^"]*}}.foo"
+# CHECK-NOT: note
+# CHECK-NOT: error
+# CHECK: $ "echo" "foo"
+# CHECK: $ "diff" "-u" "{{[^"]*}}.foo" "-"
+# CHECK-NOT: note
+# CHECK-NOT: error
+# CHECK: $ "echo" "bar"
+# CHECK: $ "diff" "-u" "{{[^"]*}}.foo" "-"
+# CHECK: # command output:
+# CHECK:      @@
+# CHECK-NEXT: -foo
+# CHECK-NEXT: +bar
+# CHECK: error: command failed with exit status: 1
+# CHECK: ***
+
+# CHECK: FAIL: shtest-shell :: diff-pipes-2.txt
+# CHECK: *** TEST 'shtest-shell :: diff-pipes-2.txt' FAILED ***
+# CHECK: $ "echo" "bar"
+# CHECK: $ "diff" "-u" "-" "{{[^"]*}}.foo"
+# CHECK: # command output:
+# CHECK:      @@
+# CHECK-NEXT: -bar
+# CHECK-NEXT: +foo
+# CHECK: error: command failed with exit status: 1
+# CHECK: ***
+
+# CHECK: FAIL: shtest-shell :: diff-pipes-3.txt
+# CHECK: *** TEST 'shtest-shell :: diff-pipes-3.txt' FAILED ***
+# CHECK: $ "echo" "foo"
+# CHECK: $ "diff" "-" "{{[^"]*}}.foo"
+# CHECK-NOT: note
+# CHECK-NOT: error
+# CHECK: $ "FileCheck"
+# CHECK-NOT: note
+# CHECK-NOT: error
+# CHECK: $ "echo" "bar"
+# CHECK: $ "diff" "-u" "{{[^"]*}}.foo" "-"
+# CHECK: note: command had no output on stdout or stderr
+# CHECK: error: command failed with exit status: 1
+# CHECK: $ "FileCheck"
+# CHECK-NOT: note
+# CHECK-NOT: error
 # CHECK: ***
 
 # CHECK: FAIL: shtest-shell :: diff-r-error-0.txt
@@ -147,6 +203,20 @@
 # CHECK: File {{.*}}dir1{{.*}}extra_file is a regular empty file while file {{.*}}dir2{{.*}}extra_file is a directory
 # CHECK: error: command failed with exit status: 1
 
+# CHECK: FAIL: shtest-shell :: diff-r-error-7.txt
+# CHECK: *** TEST 'shtest-shell :: diff-r-error-7.txt' FAILED ***
+# CHECK: $ "diff" "-r" "-" "{{[^"]*}}"
+# CHECK: # command stderr:
+# CHECK: Error: cannot recursively compare '-'
+# CHECK: error: command failed with exit status: 1
+
+# CHECK: FAIL: shtest-shell :: diff-r-error-8.txt
+# CHECK: *** TEST 'shtest-shell :: diff-r-error-8.txt' FAILED ***
+# CHECK: $ "diff" "-r" "{{[^"]*}}" "-"
+# CHECK: # command stderr:
+# CHECK: Error: cannot recursively compare '-'
+# CHECK: error: command failed with exit status: 1
+
 # CHECK: PASS: shtest-shell :: diff-r.txt
 
 # CHECK: FAIL: shtest-shell :: error-0.txt
@@ -228,4 +298,4 @@
 # CHECK: PASS: shtest-shell :: sequencing-0.txt
 # CHECK: XFAIL: shtest-shell :: sequencing-1.txt
 # CHECK: PASS: shtest-shell :: valid-shell.txt
-# CHECK: Failing Tests (27)
+# CHECK: Failing Tests (32)