Index: lldb/trunk/include/lldb/Interpreter/Args.h
===================================================================
--- lldb/trunk/include/lldb/Interpreter/Args.h
+++ lldb/trunk/include/lldb/Interpreter/Args.h
@@ -18,6 +18,7 @@
 #include <utility>
 
 // Other libraries and framework includes
+#include "llvm/ADT/StringRef.h"
 // Project includes
 #include "lldb/lldb-private-types.h"
 #include "lldb/lldb-types.h"
@@ -75,11 +76,9 @@
     ///     A NULL terminated command that will be copied and split up
     ///     into arguments.
     ///
-    /// @see Args::SetCommandString(const char *)
+    /// @see Args::SetCommandString(llvm::StringRef)
     //------------------------------------------------------------------
-    Args (const char *command = NULL);
-
-    Args (const char *command, size_t len);
+    Args (llvm::StringRef command = llvm::StringRef());
 
     Args (const Args &rhs);
     
@@ -108,7 +107,7 @@
     /// that can be accessed via the accessor functions.
     ///
     /// @param[in] command
-    ///     A NULL terminated command that will be copied and split up
+    ///     A command StringRef that will be copied and split up
     ///     into arguments.
     ///
     /// @see Args::GetArgumentCount() const
@@ -118,10 +117,7 @@
     /// @see Args::Unshift (const char *)
     //------------------------------------------------------------------
     void
-    SetCommandString (const char *command);
-
-    void
-    SetCommandString (const char *command, size_t len);
+    SetCommandString (llvm::StringRef command);
 
     bool
     GetCommandString (std::string &command) const;
@@ -449,6 +445,9 @@
 
     void
     UpdateArgvFromArgs ();
+
+    llvm::StringRef
+    ParseSingleArgument (llvm::StringRef command);
 };
 
 } // namespace lldb_private
Index: lldb/trunk/source/Commands/CommandObjectExpression.cpp
===================================================================
--- lldb/trunk/source/Commands/CommandObjectExpression.cpp
+++ lldb/trunk/source/Commands/CommandObjectExpression.cpp
@@ -487,7 +487,7 @@
 
         if (end_options)
         {
-            Args args (command, end_options - command);
+            Args args (llvm::StringRef(command, end_options - command));
             if (!ParseOptions (args, result))
                 return false;
             
Index: lldb/trunk/source/Commands/CommandObjectPlatform.cpp
===================================================================
--- lldb/trunk/source/Commands/CommandObjectPlatform.cpp
+++ lldb/trunk/source/Commands/CommandObjectPlatform.cpp
@@ -2142,7 +2142,7 @@
             
             if (end_options)
             {
-                Args args (raw_command_line, end_options - raw_command_line);
+                Args args (llvm::StringRef(raw_command_line, end_options - raw_command_line));
                 if (!ParseOptions (args, result))
                     return false;
             }
Index: lldb/trunk/source/Commands/CommandObjectWatchpoint.cpp
===================================================================
--- lldb/trunk/source/Commands/CommandObjectWatchpoint.cpp
+++ lldb/trunk/source/Commands/CommandObjectWatchpoint.cpp
@@ -1211,7 +1211,7 @@
             
             if (end_options)
             {
-                Args args (raw_command, end_options - raw_command);
+                Args args (llvm::StringRef(raw_command, end_options - raw_command));
                 if (!ParseOptions (args, result))
                     return false;
                 
Index: lldb/trunk/source/Interpreter/Args.cpp
===================================================================
--- lldb/trunk/source/Interpreter/Args.cpp
+++ lldb/trunk/source/Interpreter/Args.cpp
@@ -33,25 +33,15 @@
 //----------------------------------------------------------------------
 // Args constructor
 //----------------------------------------------------------------------
-Args::Args (const char *command) :
+Args::Args (llvm::StringRef command) :
     m_args(),
     m_argv(),
     m_args_quote_char()
 {
-    if (command)
-        SetCommandString (command);
+    SetCommandString (command);
 }
 
 
-Args::Args (const char *command, size_t len) :
-    m_args(),
-    m_argv(),
-    m_args_quote_char()
-{
-    if (command && len)
-        SetCommandString (command, len);
-}
-
 //----------------------------------------------------------------------
 // We have to be very careful on the copy constructor of this class
 // to make sure we copy all of the string values, but we can't copy the
@@ -146,214 +136,159 @@
     return argc > 0;
 }
 
-void
-Args::SetCommandString (const char *command, size_t len)
-{
-    // Use std::string to make sure we get a NULL terminated string we can use
-    // as "command" could point to a string within a large string....
-    std::string null_terminated_command(command, len);
-    SetCommandString(null_terminated_command.c_str());
-}
+// A helper function for argument parsing.
+// Parses the initial part of the first argument using normal double quote rules:
+// backslash escapes the double quote and itself. The parsed string is appended to the second
+// argument. The function returns the unparsed portion of the string, starting at the closing
+// quote.
+static llvm::StringRef
+ParseDoubleQuotes(llvm::StringRef quoted, std::string &result)
+{
+    // Inside double quotes, '\' and '"' are special.
+    static const char *k_escapable_characters = "\"\\";
+    while (true)
+    {
+        // Skip over over regular characters and append them.
+        size_t regular = quoted.find_first_of(k_escapable_characters);
+        result += quoted.substr(0, regular);
+        quoted = quoted.substr(regular);
 
-void
-Args::SetCommandString (const char *command)
-{
-    m_args.clear();
-    m_argv.clear();
-    m_args_quote_char.clear();
+        // If we have reached the end of string or the closing quote, we're done.
+        if (quoted.empty() || quoted.front() == '"')
+            break;
 
-    if (command && command[0])
-    {
-        static const char *k_space_separators = " \t";
-        static const char *k_escapable_characters = " \t\\'\"";
-        const char *arg_end = nullptr;
-        const char *arg_pos;
-        for (arg_pos = command;
-             arg_pos && arg_pos[0];
-             arg_pos = arg_end)
+        // We have found a backslash.
+        quoted = quoted.drop_front();
+
+        if (quoted.empty())
         {
-            // Skip any leading space separators
-            const char *arg_start = ::strspn (arg_pos, k_space_separators) + arg_pos;
-            
-            // If there were only space separators to the end of the line, then
-            // we're done.
-            if (*arg_start == '\0')
-                break;
+            // A lone backslash at the end of string, let's just append it.
+            result += '\\';
+            break;
+        }
 
-            // Arguments can be split into multiple discontiguous pieces,
-            // for example:
-            //  "Hello ""World"
-            // this would result in a single argument "Hello World" (without/
-            // the quotes) since the quotes would be removed and there is 
-            // not space between the strings. So we need to keep track of the
-            // current start of each argument piece in "arg_piece_start"
-            const char *arg_piece_start = arg_start;
-            arg_pos = arg_piece_start;
-
-            std::string arg;
-            // Since we can have multiple quotes that form a single command
-            // in a command like: "Hello "world'!' (which will make a single
-            // argument "Hello world!") we remember the first quote character
-            // we encounter and use that for the quote character.
-            char first_quote_char = '\0';
-            char quote_char = '\0';
-            bool arg_complete = false;
+        // If the character after the backslash is not a whitelisted escapable character, we
+        // leave the character sequence untouched.
+        if (strchr(k_escapable_characters, quoted.front()) == nullptr)
+            result += '\\';
+
+        result += quoted.front();
+        quoted = quoted.drop_front();
+    }
+
+    return quoted;
+}
+
+// A helper function for SetCommandString.
+// Parses a single argument from the command string, processing quotes and backslashes in a
+// shell-like manner. The parsed argument is appended to the m_args array. The function returns
+// the unparsed portion of the string, starting at the first unqouted, unescaped whitespace
+// character.
+llvm::StringRef
+Args::ParseSingleArgument(llvm::StringRef command)
+{
+    // Argument can be split into multiple discontiguous pieces,
+    // for example:
+    //  "Hello ""World"
+    // this would result in a single argument "Hello World" (without/
+    // the quotes) since the quotes would be removed and there is
+    // not space between the strings.
+
+    std::string arg;
+
+    // Since we can have multiple quotes that form a single command
+    // in a command like: "Hello "world'!' (which will make a single
+    // argument "Hello world!") we remember the first quote character
+    // we encounter and use that for the quote character.
+    char first_quote_char = '\0';
+
+    bool arg_complete = false;
+    do
+    {
+        // Skip over over regular characters and append them.
+        size_t regular = command.find_first_of(" \t\"'`\\");
+        arg += command.substr(0, regular);
+        command = command.substr(regular);
+
+        if (command.empty())
+            break;
 
-            do
+        char special = command.front();
+        command = command.drop_front();
+        switch (special)
+        {
+        case '\\':
+            if (command.empty())
             {
-                arg_end = ::strcspn (arg_pos, k_escapable_characters) + arg_pos;
+                arg += '\\';
+                break;
+            }
 
-                switch (arg_end[0])
-                {
-                default:
-                    assert (!"Unhandled case statement, we must handle this...");
-                    break;
+            // If the character after the backslash is not a whitelisted escapable character, we
+            // leave the character sequence untouched.
+            static const char *k_escapable_characters = " \t\\'\"`";
+            if (strchr(k_escapable_characters, command.front()) == nullptr)
+                arg += '\\';
 
-                case '\0':
-                    // End of C string
-                    if (arg_piece_start && arg_piece_start[0])
-                        arg.append (arg_piece_start);
-                    arg_complete = true;
-                    break;
-                case '\\':
-                    // Backslash character
-                    switch (arg_end[1])
-                    {
-                        case '\0':
-                            arg.append (arg_piece_start);
-                            ++arg_end;
-                            arg_complete = true;
-                            break;
-
-                        default:
-                            // Only consider this two-character sequence an escape sequence if we're unquoted and
-                            // the character after the backslash is a whitelisted escapable character.  Otherwise
-                            // leave the character sequence untouched.
-                            if (quote_char == '\0' && (nullptr != strchr(k_escapable_characters, arg_end[1])))
-                            {
-                                arg.append (arg_piece_start, arg_end - arg_piece_start);
-                                arg.append (arg_end + 1, 1);
-                                arg_pos = arg_end + 2;
-                                arg_piece_start = arg_pos;
-                            }
-                            else
-                                arg_pos = arg_end + 2;
-                            break;
-                    }
-                    break;
-                case '"':
-                case '\'':
-                case '`':
-                    // Quote characters 
-                    if (quote_char)
-                    {
-                        // We found a quote character while inside a quoted
-                        // character argument. If it matches our current quote
-                        // character, this ends the effect of the quotes. If it
-                        // doesn't we ignore it.
-                        if (quote_char == arg_end[0])
-                        {
-                            arg.append (arg_piece_start, arg_end - arg_piece_start);
-                            // Clear the quote character and let parsing
-                            // continue (we need to watch for things like:
-                            // "Hello ""World"
-                            // "Hello "World
-                            // "Hello "'World'
-                            // All of which will result in a single argument "Hello World"
-                            quote_char = '\0'; // Note that we are no longer inside quotes
-                            arg_pos = arg_end + 1; // Skip the quote character
-                            arg_piece_start = arg_pos; // Note we are starting from later in the string
-                        }
-                        else
-                        {
-                            // different quote, skip it and keep going
-                            arg_pos = arg_end + 1;
-                        }
-                    }
-                    else
-                    {
-                        // We found the start of a quote scope.
-                        // Make sure there isn't a string that precedes
-                        // the start of a quote scope like:
-                        // Hello" World"
-                        // If so, then add the "Hello" to the arg
-                        if (arg_end > arg_piece_start)
-                            arg.append (arg_piece_start, arg_end - arg_piece_start);
-                            
-                        // Enter into a quote scope
-                        quote_char = arg_end[0];
-                        
-                        if (first_quote_char == '\0')
-                            first_quote_char = quote_char;
+            arg += command.front();
+            command.drop_front();
 
-                        arg_pos = arg_end;
-                        ++arg_pos;                 // Skip the quote character
-                        arg_piece_start = arg_pos; // Note we are starting from later in the string
-                        
-                        // Skip till the next quote character
-                        const char *end_quote = ::strchr (arg_piece_start, quote_char);
-                        while (end_quote && end_quote[-1] == '\\')
-                        {
-                            // Don't skip the quote character if it is 
-                            // preceded by a '\' character
-                            end_quote = ::strchr (end_quote + 1, quote_char);
-                        }
-                        
-                        if (end_quote)
-                        {
-                            if (end_quote > arg_piece_start)
-                                arg.append (arg_piece_start, end_quote - arg_piece_start);
+            break;
 
-                            // If the next character is a space or the end of 
-                            // string, this argument is complete...
-                            if (end_quote[1] == ' ' || end_quote[1] == '\t' || end_quote[1] == '\0')
-                            {
-                                arg_complete = true;
-                                arg_end = end_quote + 1;
-                            }
-                            else
-                            {
-                                arg_pos = end_quote + 1;
-                                arg_piece_start = arg_pos;
-                            }
-                            quote_char = '\0';
-                        }
-                        else
-                        {
-                            // Consume the rest of the string as there was no terminating quote
-                            arg.append(arg_piece_start);
-                            arg_end = arg_piece_start + strlen(arg_piece_start);
-                            arg_complete = true;
-                        }
-                    }
-                    break;
+        case ' ':
+        case '\t':
+            // We are not inside any quotes, we just found a space after an
+            // argument. We are done.
+            arg_complete = true;
+            break;
 
-                case ' ':
-                case '\t':
-                    if (quote_char)
-                    {
-                        // We are currently processing a quoted character and found
-                        // a space character, skip any spaces and keep trying to find
-                        // the end of the argument. 
-                        arg_pos = ::strspn (arg_end, k_space_separators) + arg_end;
-                    }
-                    else
-                    {
-                        // We are not inside any quotes, we just found a space after an
-                        // argument
-                        if (arg_end > arg_piece_start)
-                            arg.append (arg_piece_start, arg_end - arg_piece_start);
-                        arg_complete = true;
-                    }
-                    break;
-                }
-            } while (!arg_complete);
+        case '"':
+        case '\'':
+        case '`':
+            // We found the start of a quote scope.
+            if (first_quote_char == '\0')
+                first_quote_char = special;
 
-            m_args.push_back(arg);
-            m_args_quote_char.push_back (first_quote_char);
+            if (special == '"')
+                command = ParseDoubleQuotes(command, arg);
+            else
+            {
+                // For single quotes, we simply skip ahead to the matching quote character
+                // (or the end of the string).
+                size_t quoted = command.find(special);
+                arg += command.substr(0, quoted);
+                command = command.substr(quoted);
+            }
+
+            // If we found a closing quote, skip it.
+            if (! command.empty())
+                command = command.drop_front();
+
+            break;
         }
-        UpdateArgvFromArgs();
+    } while (!arg_complete);
+
+    m_args.push_back(arg);
+    m_args_quote_char.push_back (first_quote_char);
+    return command;
+}
+
+void
+Args::SetCommandString (llvm::StringRef command)
+{
+    m_args.clear();
+    m_argv.clear();
+    m_args_quote_char.clear();
+
+    static const char *k_space_separators = " \t";
+    command = command.ltrim(k_space_separators);
+    while (!command.empty())
+    {
+        command = ParseSingleArgument(command);
+        command = command.ltrim(k_space_separators);
     }
+
+    UpdateArgvFromArgs();
 }
 
 void
Index: lldb/trunk/source/Interpreter/CommandInterpreter.cpp
===================================================================
--- lldb/trunk/source/Interpreter/CommandInterpreter.cpp
+++ lldb/trunk/source/Interpreter/CommandInterpreter.cpp
@@ -1412,7 +1412,7 @@
                                       CommandReturnObject &result)
 {
     CommandObject *alias_cmd_obj = nullptr;
-    Args cmd_args (raw_input_string.c_str());
+    Args cmd_args (raw_input_string);
     alias_cmd_obj = GetCommandObject (alias_name);
     StreamString result_str;
     
@@ -2082,8 +2082,8 @@
     // We parse the argument up to the cursor, so the last argument in parsed_line is
     // the one containing the cursor, and the cursor is after the last character.
 
-    Args parsed_line(current_line, last_char - current_line);
-    Args partial_parsed_line(current_line, cursor - current_line);
+    Args parsed_line(llvm::StringRef(current_line, last_char - current_line));
+    Args partial_parsed_line(llvm::StringRef(current_line, cursor - current_line));
 
     // Don't complete comments, and if the line we are completing is just the history repeat character, 
     // substitute the appropriate history line.
Index: lldb/trunk/test/settings/quoting/Makefile
===================================================================
--- lldb/trunk/test/settings/quoting/Makefile
+++ lldb/trunk/test/settings/quoting/Makefile
@@ -0,0 +1,5 @@
+LEVEL = ../../make
+
+C_SOURCES := main.c
+
+include $(LEVEL)/Makefile.rules
Index: lldb/trunk/test/settings/quoting/TestQuoting.py
===================================================================
--- lldb/trunk/test/settings/quoting/TestQuoting.py
+++ lldb/trunk/test/settings/quoting/TestQuoting.py
@@ -0,0 +1,82 @@
+"""
+Test quoting of arguments to lldb commands
+"""
+
+import os, time, re
+import unittest2
+import lldb
+from lldbtest import *
+
+class SettingsCommandTestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @classmethod
+    def classCleanup(cls):
+        """Cleanup the test byproducts."""
+        cls.RemoveTempFile("stdout.txt")
+
+    def test_no_quote(self):
+        self.do_test_args("a b c", "a\0b\0c\0")
+
+    def test_single_quote(self):
+        self.do_test_args("'a b c'", "a b c\0")
+
+    def test_double_quote(self):
+        self.do_test_args('"a b c"', "a b c\0")
+
+    def test_double_quote(self):
+        self.do_test_args('"a b c"', 'a b c\0')
+
+    def test_single_quote_escape(self):
+        self.do_test_args("'a b\\' c", "a b\\\0c\0")
+
+    def test_double_quote_escape(self):
+        self.do_test_args('"a b\\" c"', 'a b" c\0')
+
+    def test_double_quote_escape(self):
+        self.do_test_args('"a b\\" c"', 'a b" c\0')
+
+    def test_double_quote_escape2(self):
+        self.do_test_args('"a b\\\\" c', 'a b\\\0c\0')
+
+    def test_double_quote_escape2(self):
+        self.do_test_args('"a b\\\\" c', 'a b\\\0c\0')
+
+    def test_single_in_double(self):
+        self.do_test_args('"a\'b"', "a'b\0")
+
+    def test_double_in_single(self):
+        self.do_test_args("'a\"b'", 'a"b\0')
+
+    def test_combined(self):
+        self.do_test_args('"a b"c\'d e\'', 'a bcd e\0')
+
+    def test_bare_single(self):
+        self.do_test_args("a\\'b", "a'b\0")
+
+    def test_bare_double(self):
+        self.do_test_args('a\\"b', 'a"b\0')
+
+    def do_test_args(self, args_in, args_out):
+        """Test argument parsing. Run the program with args_in. The program dumps its arguments
+        to stdout. Compare the stdout with args_out."""
+        self.buildDefault()
+
+        exe = os.path.join(os.getcwd(), "a.out")
+        self.runCmd("file " + exe, CURRENT_EXECUTABLE_SET)
+
+        self.runCmd("process launch -o stdout.txt -- " + args_in)
+
+        with open('stdout.txt', 'r') as f:
+            output = f.read()
+
+        self.RemoveTempFile("stdout.txt")
+
+        self.assertEqual(output, args_out)
+
+if __name__ == '__main__':
+    import atexit
+    lldb.SBDebugger.Initialize()
+    atexit.register(lambda: lldb.SBDebugger.Terminate())
+    unittest2.main()
Index: lldb/trunk/test/settings/quoting/main.c
===================================================================
--- lldb/trunk/test/settings/quoting/main.c
+++ lldb/trunk/test/settings/quoting/main.c
@@ -0,0 +1,13 @@
+#include <stdio.h>
+#include <string.h>
+
+/* This program writes its arguments (separated by '\0') to stdout. */
+int
+main(int argc, char const *argv[])
+{
+    int i;
+    for (i = 1; i < argc; ++i)
+        fwrite(argv[i], strlen(argv[i])+1, 1, stdout);
+
+    return 0;
+}