diff --git a/bitbake/lib/bb/pysh/interp.py b/bitbake/lib/bb/pysh/interp.py
new file mode 100644
index 0000000..25d8c92
--- /dev/null
+++ b/bitbake/lib/bb/pysh/interp.py
@@ -0,0 +1,1367 @@
+# interp.py - shell interpreter for pysh.
+#
+# Copyright 2007 Patrick Mezard
+#
+# This software may be used and distributed according to the terms
+# of the GNU General Public License, incorporated herein by reference.
+
+"""Implement the shell interpreter.
+
+Most references are made to "The Open Group Base Specifications Issue 6".
+<http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html>
+"""
+# TODO: document the fact input streams must implement fileno() so Popen will work correctly.
+# it requires non-stdin stream to be implemented as files. Still to be tested...
+# DOC: pathsep is used in PATH instead of ':'. Clearly, there are path syntax issues here.
+# TODO: stop command execution upon error.
+# TODO: sort out the filename/io_number mess. It should be possible to use filenames only.
+# TODO: review subshell implementation
+# TODO: test environment cloning for non-special builtins
+# TODO: set -x should not rebuild commands from tokens, assignments/redirections are lost
+# TODO: unit test for variable assignment
+# TODO: test error management wrt error type/utility type
+# TODO: test for binary output everywhere
+# BUG: debug-parsing does not pass log file to PLY. Maybe a PLY upgrade is necessary.
+import base64
+import cPickle as pickle
+import errno
+import glob
+import os
+import re
+import subprocess
+import sys
+import tempfile
+
+try:
+    s = set()
+    del s
+except NameError:
+    from Set import Set as set
+
+import builtin
+from sherrors import *
+import pyshlex
+import pyshyacc
+
+def mappend(func, *args, **kargs):
+    """Like map but assume func returns a list. Returned lists are merged into
+    a single one.
+    """
+    return reduce(lambda a,b: a+b, map(func, *args, **kargs), [])
+
+class FileWrapper:
+    """File object wrapper to ease debugging.
+    
+    Allow mode checking and implement file duplication through a simple 
+    reference counting scheme. Not sure the latter is really useful since
+    only real file descriptors can be used.
+    """
+    def __init__(self, mode, file, close=True):
+        if mode not in ('r', 'w', 'a'):
+            raise IOError('invalid mode: %s' % mode)
+        self._mode = mode
+        self._close = close
+        if isinstance(file, FileWrapper):
+            if file._refcount[0] <= 0:
+                raise IOError(0, 'Error')
+            self._refcount = file._refcount
+            self._refcount[0] += 1
+            self._file = file._file
+        else:
+            self._refcount = [1]
+            self._file = file
+        
+    def dup(self):
+        return FileWrapper(self._mode, self, self._close)
+        
+    def fileno(self):
+        """fileno() should be only necessary for input streams."""
+        return self._file.fileno()
+        
+    def read(self, size=-1):
+        if self._mode!='r':
+            raise IOError(0, 'Error')
+        return self._file.read(size)
+        
+    def readlines(self, *args, **kwargs):
+        return self._file.readlines(*args, **kwargs)
+        
+    def write(self, s):
+        if self._mode not in ('w', 'a'):
+            raise IOError(0, 'Error')
+        return self._file.write(s)
+        
+    def flush(self):
+        self._file.flush()
+        
+    def close(self):        
+        if not self._refcount:
+            return
+        assert  self._refcount[0] > 0
+        
+        self._refcount[0] -= 1    
+        if self._refcount[0] == 0:
+            self._mode = 'c'
+            if self._close:
+                self._file.close()
+        self._refcount = None
+                
+    def mode(self):
+        return self._mode
+
+    def __getattr__(self, name):
+        if name == 'name':
+            self.name = getattr(self._file, name)
+            return self.name
+        else:
+            raise AttributeError(name)
+
+    def __del__(self):
+        self.close()
+               
+               
+def win32_open_devnull(mode):
+    return open('NUL', mode)
+    
+        
+class Redirections:
+    """Stores open files and their mapping to pseudo-sh file descriptor.
+    """
+    # BUG: redirections are not handled correctly: 1>&3 2>&3 3>&4 does 
+    # not make 1 to redirect to 4
+    def __init__(self, stdin=None, stdout=None, stderr=None):
+        self._descriptors = {}
+        if stdin is not None:
+            self._add_descriptor(0, stdin)
+        if stdout is not None:
+            self._add_descriptor(1, stdout)
+        if stderr is not None:
+            self._add_descriptor(2, stderr)
+            
+    def add_here_document(self, interp, name, content, io_number=None):
+        if io_number is None:
+            io_number = 0
+            
+        if name==pyshlex.unquote_wordtree(name):
+            content = interp.expand_here_document(('TOKEN', content))
+    
+        # Write document content in a temporary file
+        tmp = tempfile.TemporaryFile()
+        try:
+            tmp.write(content)
+            tmp.flush()
+            tmp.seek(0)
+            self._add_descriptor(io_number, FileWrapper('r', tmp))
+        except:
+            tmp.close()
+            raise                
+        
+    def add(self, interp, op, filename, io_number=None):
+        if op not in ('<', '>', '>|', '>>', '>&'):
+            # TODO: add descriptor duplication and here_documents      
+            raise RedirectionError('Unsupported redirection operator "%s"' % op)
+            
+        if io_number is not None:
+            io_number = int(io_number)
+            
+        if (op == '>&' and filename.isdigit()) or filename=='-':
+            # No expansion for file descriptors, quote them if you want a filename
+            fullname = filename
+        else:
+            if filename.startswith('/'):
+                # TODO: win32 kludge
+                if filename=='/dev/null':
+                    fullname = 'NUL'
+                else:
+                    # TODO: handle absolute pathnames, they are unlikely to exist on the
+                    # current platform (win32 for instance).
+                    raise NotImplementedError()
+            else:
+                fullname = interp.expand_redirection(('TOKEN', filename))
+                if not fullname:
+                    raise RedirectionError('%s: ambiguous redirect' % filename)
+                # Build absolute path based on PWD
+                fullname = os.path.join(interp.get_env()['PWD'], fullname)
+            
+        if op=='<':
+            return self._add_input_redirection(interp, fullname, io_number)
+        elif op in ('>', '>|'):
+            clobber = ('>|'==op)
+            return self._add_output_redirection(interp, fullname, io_number, clobber)
+        elif op=='>>':
+            return self._add_output_appending(interp, fullname, io_number)
+        elif op=='>&':
+            return self._dup_output_descriptor(fullname, io_number)
+        
+    def close(self):
+        if self._descriptors is not None:
+            for desc in self._descriptors.itervalues():
+                desc.flush()
+                desc.close()
+            self._descriptors = None
+            
+    def stdin(self):
+        return self._descriptors[0]
+          
+    def stdout(self):
+        return self._descriptors[1] 
+        
+    def stderr(self):
+        return self._descriptors[2] 
+            
+    def clone(self):
+        clone = Redirections()
+        for desc, fileobj in self._descriptors.iteritems():
+            clone._descriptors[desc] = fileobj.dup()
+        return clone
+           
+    def _add_output_redirection(self, interp, filename, io_number, clobber):    
+        if io_number is None:
+            # io_number default to standard output
+            io_number = 1
+        
+        if not clobber and interp.get_env().has_opt('-C') and os.path.isfile(filename):
+            # File already exist in no-clobber mode, bail out
+            raise RedirectionError('File "%s" already exists' % filename)
+            
+        # Open and register
+        self._add_file_descriptor(io_number, filename, 'w')
+        
+    def _add_output_appending(self, interp, filename, io_number):    
+        if io_number is None:
+            io_number = 1
+        self._add_file_descriptor(io_number, filename, 'a')
+            
+    def _add_input_redirection(self, interp, filename, io_number):
+        if io_number is None:
+            io_number = 0
+        self._add_file_descriptor(io_number, filename, 'r')
+        
+    def _add_file_descriptor(self, io_number, filename, mode):    
+        try:            
+            if filename.startswith('/'):
+                if filename=='/dev/null':
+                    f = win32_open_devnull(mode+'b')
+                else:
+                    # TODO: handle absolute pathnames, they are unlikely to exist on the
+                    # current platform (win32 for instance).
+                    raise NotImplementedError('cannot open absolute path %s' % repr(filename))
+            else:
+                f = file(filename, mode+'b')
+        except IOError as e:
+            raise RedirectionError(str(e))
+            
+        wrapper = None
+        try:
+            wrapper = FileWrapper(mode, f)
+            f = None
+            self._add_descriptor(io_number, wrapper)
+        except:
+            if f: f.close()
+            if wrapper: wrapper.close()
+            raise
+            
+    def _dup_output_descriptor(self, source_fd, dest_fd):
+        if source_fd is None:
+            source_fd = 1
+        self._dup_file_descriptor(source_fd, dest_fd, 'w')
+            
+    def _dup_file_descriptor(self, source_fd, dest_fd, mode):
+        source_fd = int(source_fd)
+        if source_fd not in self._descriptors:
+            raise RedirectionError('"%s" is not a valid file descriptor' % str(source_fd))
+        source = self._descriptors[source_fd]
+        
+        if source.mode()!=mode:
+            raise RedirectionError('Descriptor %s cannot be duplicated in mode "%s"' % (str(source), mode))
+        
+        if dest_fd=='-':
+            # Close the source descriptor
+            del self._descriptors[source_fd]
+            source.close()
+        else:
+            dest_fd = int(dest_fd)
+            if dest_fd not in self._descriptors:
+                raise RedirectionError('Cannot replace file descriptor %s' % str(dest_fd))
+                
+            dest = self._descriptors[dest_fd]
+            if dest.mode()!=mode:
+                raise RedirectionError('Descriptor %s cannot be cannot be redirected in mode "%s"' % (str(dest), mode))
+            
+            self._descriptors[dest_fd] = source.dup()
+            dest.close()        
+            
+    def _add_descriptor(self, io_number, file):
+        io_number = int(io_number)
+        
+        if io_number in self._descriptors:
+            # Close the current descriptor
+            d = self._descriptors[io_number]
+            del self._descriptors[io_number]
+            d.close()
+            
+        self._descriptors[io_number] = file
+
+    def __str__(self):
+        names = [('%d=%r' % (k, getattr(v, 'name', None))) for k,v
+                 in self._descriptors.iteritems()]
+        names = ','.join(names)
+        return 'Redirections(%s)' % names
+
+    def __del__(self):
+        self.close()
+    
+def cygwin_to_windows_path(path):
+    """Turn /cygdrive/c/foo into c:/foo, or return path if it
+    is not a cygwin path.
+    """
+    if not path.startswith('/cygdrive/'):
+        return path
+    path = path[len('/cygdrive/'):]
+    path = path[:1] + ':' + path[1:]
+    return path
+    
+def win32_to_unix_path(path):
+    if path is not None:
+        path = path.replace('\\', '/')
+    return path    
+    
+_RE_SHEBANG = re.compile(r'^\#!\s?([^\s]+)(?:\s([^\s]+))?')
+_SHEBANG_CMDS = {
+    '/usr/bin/env': 'env',
+    '/bin/sh': 'pysh',
+    'python': 'python',
+}
+    
+def resolve_shebang(path, ignoreshell=False):
+    """Return a list of arguments as shebang interpreter call or an empty list
+    if path does not refer to an executable script.
+    See <http://www.opengroup.org/austin/docs/austin_51r2.txt>.
+    
+    ignoreshell - set to True to ignore sh shebangs. Return an empty list instead.
+    """
+    try:
+        f = file(path)
+        try:
+            # At most 80 characters in the first line
+            header = f.read(80).splitlines()[0]
+        finally:
+            f.close()
+            
+        m = _RE_SHEBANG.search(header)
+        if not m:
+            return []
+        cmd, arg = m.group(1,2)
+        if os.path.isfile(cmd):
+            # Keep this one, the hg script for instance contains a weird windows
+            # shebang referencing the current python install.
+            cmdfile = os.path.basename(cmd).lower()
+            if cmdfile == 'python.exe':
+                cmd = 'python'
+            pass
+        elif cmd not in _SHEBANG_CMDS:
+            raise CommandNotFound('Unknown interpreter "%s" referenced in '\
+                'shebang' % header)
+        cmd = _SHEBANG_CMDS.get(cmd)
+        if cmd is None or (ignoreshell and cmd == 'pysh'):
+            return []
+        if arg is None:
+            return [cmd, win32_to_unix_path(path)]
+        return [cmd, arg, win32_to_unix_path(path)]
+    except IOError as e:
+        if  e.errno!=errno.ENOENT and \
+            (e.errno!=errno.EPERM and not os.path.isdir(path)): # Opening a directory raises EPERM
+            raise
+        return []
+        
+def win32_find_in_path(name, path):
+    if isinstance(path, str):
+        path = path.split(os.pathsep)
+        
+    exts = os.environ.get('PATHEXT', '').lower().split(os.pathsep)
+    for p in path:
+        p_name = os.path.join(p, name)
+        
+        prefix = resolve_shebang(p_name)
+        if prefix:
+            return prefix
+            
+        for ext in exts:    
+            p_name_ext = p_name + ext
+            if os.path.exists(p_name_ext):
+                return [win32_to_unix_path(p_name_ext)]
+    return []
+
+class Traps(dict):
+    def __setitem__(self, key, value):
+        if key not in ('EXIT',):
+            raise NotImplementedError()
+        super(Traps, self).__setitem__(key, value)
+
+# IFS white spaces character class
+_IFS_WHITESPACES = (' ', '\t', '\n')
+
+class Environment:
+    """Environment holds environment variables, export table, function 
+    definitions and whatever is defined in 2.12 "Shell Execution Environment",
+    redirection excepted.
+    """
+    def __init__(self, pwd):
+        self._opt = set()       #Shell options
+        
+        self._functions = {}        
+        self._env = {'?': '0', '#': '0'}
+        self._exported = set([
+            'HOME', 'IFS', 'PATH'
+        ])
+        
+        # Set environment vars with side-effects
+        self._ifs_ws = None     # Set of IFS whitespace characters
+        self._ifs_re = None     # Regular expression used to split between words using IFS classes
+        self['IFS'] = ''.join(_IFS_WHITESPACES) #Default environment values
+        self['PWD'] = pwd
+        self.traps = Traps()
+        
+    def clone(self, subshell=False):
+        env = Environment(self['PWD'])
+        env._opt = set(self._opt)
+        for k,v in self.get_variables().iteritems():
+            if k in self._exported:
+                env.export(k,v)
+            elif subshell:
+                env[k] = v
+                
+        if subshell:
+            env._functions = dict(self._functions)
+            
+        return env        
+        
+    def __getitem__(self, key):
+        if key in ('@', '*', '-', '$'):
+            raise NotImplementedError('%s is not implemented' % repr(key))
+        return self._env[key]
+        
+    def get(self, key, defval=None):
+        try:
+            return self[key]
+        except KeyError:
+            return defval
+        
+    def __setitem__(self, key, value):
+        if key=='IFS':
+            # Update the whitespace/non-whitespace classes
+            self._update_ifs(value)
+        elif key=='PWD':
+            pwd = os.path.abspath(value)
+            if not os.path.isdir(pwd):
+                raise VarAssignmentError('Invalid directory %s' % value)
+            value = pwd
+        elif key in ('?', '!'):
+            value = str(int(value))
+        self._env[key] = value
+        
+    def __delitem__(self, key):
+        if key in ('IFS', 'PWD', '?'):
+            raise VarAssignmentError('%s cannot be unset' % key)
+        del self._env[key]
+
+    def __contains__(self, item):
+        return item in self._env
+        
+    def set_positional_args(self, args):
+        """Set the content of 'args' as positional argument from 1 to len(args).
+        Return previous argument as a list of strings.
+        """
+        # Save and remove previous arguments
+        prevargs = []        
+        for i in xrange(int(self._env['#'])):
+            i = str(i+1)
+            prevargs.append(self._env[i])
+            del self._env[i]
+        self._env['#'] = '0'
+                
+        #Set new ones
+        for i,arg in enumerate(args):
+            self._env[str(i+1)] = str(arg)
+        self._env['#'] = str(len(args))
+        
+        return prevargs
+        
+    def get_positional_args(self):
+        return [self._env[str(i+1)] for i in xrange(int(self._env['#']))]
+        
+    def get_variables(self):
+        return dict(self._env)
+        
+    def export(self, key, value=None):
+        if value is not None:
+            self[key] = value
+        self._exported.add(key)
+        
+    def get_exported(self):
+        return [(k,self._env.get(k)) for k in self._exported]
+            
+    def split_fields(self, word):
+        if not self._ifs_ws or not word:
+            return [word]
+        return re.split(self._ifs_re, word)
+   
+    def _update_ifs(self, value):
+        """Update the split_fields related variables when IFS character set is
+        changed.
+        """
+        # TODO: handle NULL IFS
+        
+        # Separate characters in whitespace and non-whitespace
+        chars = set(value)
+        ws = [c for c in chars if c in _IFS_WHITESPACES]
+        nws = [c for c in chars if c not in _IFS_WHITESPACES]
+        
+        # Keep whitespaces in a string for left and right stripping
+        self._ifs_ws = ''.join(ws)
+        
+        # Build a regexp to split fields
+        trailing = '[' + ''.join([re.escape(c) for c in ws]) + ']'
+        if nws:
+            # First, the single non-whitespace occurence.
+            nws = '[' + ''.join([re.escape(c) for c in nws]) + ']'
+            nws = '(?:' + trailing + '*' + nws + trailing + '*' + '|' + trailing + '+)'
+        else:
+            # Then mix all parts with quantifiers
+            nws = trailing + '+'
+        self._ifs_re = re.compile(nws)
+       
+    def has_opt(self, opt, val=None):
+        return (opt, val) in self._opt
+        
+    def set_opt(self, opt, val=None):
+        self._opt.add((opt, val))
+        
+    def find_in_path(self, name, pwd=False):
+        path = self._env.get('PATH', '').split(os.pathsep)
+        if pwd:
+            path[:0] = [self['PWD']]
+        if os.name == 'nt':
+            return win32_find_in_path(name, self._env.get('PATH', ''))
+        else:
+            raise NotImplementedError()
+            
+    def define_function(self, name, body):
+        if not is_name(name):
+            raise ShellSyntaxError('%s is not a valid function name' % repr(name))
+        self._functions[name] = body
+        
+    def remove_function(self, name):
+        del self._functions[name]
+        
+    def is_function(self, name):
+        return name in self._functions
+        
+    def get_function(self, name):
+        return self._functions.get(name)
+        
+       
+name_charset = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_'
+name_charset = dict(zip(name_charset,name_charset))
+           
+def match_name(s):
+    """Return the length in characters of the longest prefix made of name
+    allowed characters in s.
+    """
+    for i,c in enumerate(s):
+        if c not in name_charset:
+            return s[:i]
+    return s
+    
+def is_name(s):
+    return len([c for c in s if c not in name_charset])<=0
+    
+def is_special_param(c):
+    return len(c)==1 and c in ('@','*','#','?','-','$','!','0')
+    
+def utility_not_implemented(name, *args, **kwargs):
+    raise NotImplementedError('%s utility is not implemented' % name)
+    
+
+class Utility:
+    """Define utilities properties:
+    func -- utility callable. See builtin module for utility samples.
+    is_special -- see XCU 2.8.
+    """
+    def __init__(self, func, is_special=0):
+        self.func = func
+        self.is_special = bool(is_special)
+
+
+def encodeargs(args):
+    def encodearg(s):
+        lines = base64.encodestring(s)
+        lines = [l.splitlines()[0] for l in lines]
+        return ''.join(lines)
+
+    s = pickle.dumps(args)
+    return encodearg(s)
+
+def decodeargs(s):
+    s = base64.decodestring(s)
+    return pickle.loads(s)
+    
+
+class GlobError(Exception):
+    pass
+
+class Options:
+    def __init__(self):
+        # True if Mercurial operates with binary streams
+        self.hgbinary = True
+
+class Interpreter:
+    # Implementation is very basic: the execute() method just makes a DFS on the
+    # AST and execute nodes one by one. Nodes are tuple (name,obj) where name
+    # is a string identifier and obj the AST element returned by the parser.
+    #
+    # Handler are named after the node identifiers.
+    # TODO: check node names and remove the switch in execute with some
+    # dynamic getattr() call to find node handlers.
+    """Shell interpreter.
+    
+    The following debugging flags can be passed:
+    debug-parsing - enable PLY debugging.
+    debug-tree - print the generated AST.
+    debug-cmd - trace command execution before word expansion, plus exit status.
+    debug-utility - trace utility execution.
+    """
+    
+    # List supported commands.
+    COMMANDS = {
+        'cat':       Utility(builtin.utility_cat,),
+        'cd':       Utility(builtin.utility_cd,),
+        ':':        Utility(builtin.utility_colon,),
+        'echo':     Utility(builtin.utility_echo),
+        'env':      Utility(builtin.utility_env),
+        'exit':     Utility(builtin.utility_exit),
+        'export':   Utility(builtin.builtin_export,     is_special=1),
+        'egrep':    Utility(builtin.utility_egrep),
+        'fgrep':    Utility(builtin.utility_fgrep),
+        'gunzip':   Utility(builtin.utility_gunzip),
+        'kill':     Utility(builtin.utility_kill),
+        'mkdir':    Utility(builtin.utility_mkdir),
+        'netstat':  Utility(builtin.utility_netstat),
+        'printf':   Utility(builtin.utility_printf),
+        'pwd':      Utility(builtin.utility_pwd),
+        'return':   Utility(builtin.builtin_return,     is_special=1),
+        'sed':      Utility(builtin.utility_sed,),
+        'set':      Utility(builtin.builtin_set,),
+        'shift':    Utility(builtin.builtin_shift,),
+        'sleep':    Utility(builtin.utility_sleep,),
+        'sort':     Utility(builtin.utility_sort,),
+        'trap':     Utility(builtin.builtin_trap,       is_special=1),
+        'true':     Utility(builtin.utility_true),
+        'unset':    Utility(builtin.builtin_unset,      is_special=1),
+        'wait':     Utility(builtin.builtin_wait,       is_special=1),
+    }
+    
+    def __init__(self, pwd, debugflags = [], env=None, redirs=None, stdin=None,
+                 stdout=None, stderr=None, opts=Options()):
+        self._env = env
+        if self._env is None:
+            self._env = Environment(pwd)
+        self._children = {}
+            
+        self._redirs = redirs
+        self._close_redirs = False
+        
+        if self._redirs is None:
+            if stdin is None:
+                stdin = sys.stdin
+            if stdout is None:
+                stdout = sys.stdout
+            if stderr is None:
+                stderr = sys.stderr
+            stdin = FileWrapper('r', stdin, False)
+            stdout = FileWrapper('w', stdout, False)
+            stderr = FileWrapper('w', stderr, False)
+            self._redirs = Redirections(stdin, stdout, stderr)
+            self._close_redirs = True
+            
+        self._debugflags = list(debugflags)
+        self._logfile = sys.stderr
+        self._options = opts
+        
+    def close(self):
+        """Must be called when the interpreter is no longer used."""
+        script = self._env.traps.get('EXIT')
+        if script:
+            try:
+                self.execute_script(script=script)
+            except:
+                pass
+
+        if self._redirs is not None and self._close_redirs:
+            self._redirs.close()
+            self._redirs = None
+            
+    def log(self, s):
+        self._logfile.write(s)
+        self._logfile.flush()
+            
+    def __getitem__(self, key):
+        return self._env[key]
+        
+    def __setitem__(self, key, value):
+        self._env[key] = value
+
+    def options(self):
+        return self._options
+
+    def redirect(self, redirs, ios):
+        def add_redir(io):
+            if isinstance(io, pyshyacc.IORedirect):
+                redirs.add(self, io.op, io.filename, io.io_number)
+            else:
+                redirs.add_here_document(self, io.name, io.content, io.io_number)
+                    
+        map(add_redir, ios)
+        return redirs
+            
+    def execute_script(self, script=None, ast=None, sourced=False,
+                       scriptpath=None):
+        """If script is not None, parse the input. Otherwise takes the supplied
+        AST. Then execute the AST.
+        Return the script exit status.
+        """
+        try:
+            if scriptpath is not None:
+                self._env['0'] = os.path.abspath(scriptpath)
+
+            if script is not None:
+                debug_parsing = ('debug-parsing' in self._debugflags)    
+                cmds, script = pyshyacc.parse(script, True, debug_parsing)
+                if 'debug-tree' in self._debugflags:
+                    pyshyacc.print_commands(cmds, self._logfile)
+                    self._logfile.flush()
+            else:
+                cmds, script = ast, ''                
+                
+            status = 0
+            for cmd in cmds:
+                try:
+                    status = self.execute(cmd)
+                except ExitSignal as e:
+                    if sourced:
+                        raise
+                    status = int(e.args[0])
+                    return status
+                except ShellError:
+                    self._env['?'] = 1
+                    raise
+                if 'debug-utility' in self._debugflags or 'debug-cmd' in self._debugflags:
+                    self.log('returncode ' + str(status)+ '\n')
+            return status
+        except CommandNotFound as e:
+            print >>self._redirs.stderr, str(e)
+            self._redirs.stderr.flush()
+            # Command not found by non-interactive shell
+            # return 127
+            raise
+        except RedirectionError as e:
+            # TODO: should be handled depending on the utility status
+            print >>self._redirs.stderr, str(e)
+            self._redirs.stderr.flush()
+            # Command not found by non-interactive shell
+            # return 127
+            raise
+
+    def dotcommand(self, env, args):
+        if len(args) < 1:
+            raise ShellError('. expects at least one argument')
+        path = args[0]
+        if '/' not in path:
+            found = env.find_in_path(args[0], True)
+            if found:
+                path = found[0]
+        script = file(path).read()
+        return self.execute_script(script=script, sourced=True)
+
+    def execute(self, token, redirs=None):
+        """Execute and AST subtree with supplied redirections overriding default
+        interpreter ones.
+        Return the exit status.
+        """
+        if not token:
+            return 0
+            
+        if redirs is None:
+            redirs = self._redirs
+            
+        if isinstance(token, list):
+            # Commands sequence
+            res = 0
+            for t in token:
+                res = self.execute(t, redirs)
+            return res
+
+        type, value = token
+        status = 0
+        if type=='simple_command':
+            redirs_copy = redirs.clone()
+            try:
+                # TODO: define and handle command return values
+                # TODO: implement set -e
+                status = self._execute_simple_command(value, redirs_copy)
+            finally:
+                redirs_copy.close()
+        elif type=='pipeline':
+            status = self._execute_pipeline(value, redirs)
+        elif type=='and_or':
+            status = self._execute_and_or(value, redirs)
+        elif type=='for_clause':
+            status = self._execute_for_clause(value, redirs)
+        elif type=='while_clause':
+            status = self._execute_while_clause(value, redirs)
+        elif type=='function_definition':
+            status = self._execute_function_definition(value, redirs)
+        elif type=='brace_group':
+            status = self._execute_brace_group(value, redirs)
+        elif type=='if_clause':
+            status = self._execute_if_clause(value, redirs)
+        elif type=='subshell':
+            status = self.subshell(ast=value.cmds, redirs=redirs)
+        elif type=='async':
+            status = self._asynclist(value)
+        elif type=='redirect_list':
+            redirs_copy = self.redirect(redirs.clone(), value.redirs)
+            try:
+                status = self.execute(value.cmd, redirs_copy)
+            finally:
+                redirs_copy.close()
+        else:
+            raise NotImplementedError('Unsupported token type ' + type)
+
+        if status < 0:
+            status = 255
+        return status
+            
+    def _execute_if_clause(self, if_clause, redirs):
+        cond_status = self.execute(if_clause.cond, redirs)
+        if cond_status==0:
+            return self.execute(if_clause.if_cmds, redirs)
+        else:
+            return self.execute(if_clause.else_cmds, redirs)
+      
+    def _execute_brace_group(self, group, redirs):
+        status = 0
+        for cmd in group.cmds:
+            status = self.execute(cmd, redirs)
+        return status
+            
+    def _execute_function_definition(self, fundef, redirs):
+        self._env.define_function(fundef.name, fundef.body)
+        return 0
+            
+    def _execute_while_clause(self, while_clause, redirs):
+        status = 0
+        while 1:
+            cond_status = 0
+            for cond in while_clause.condition:
+                cond_status = self.execute(cond, redirs)
+                
+            if cond_status:
+                break
+                
+            for cmd in while_clause.cmds:
+                status = self.execute(cmd, redirs)
+                
+        return status
+            
+    def _execute_for_clause(self, for_clause, redirs):
+        if not is_name(for_clause.name):
+            raise ShellSyntaxError('%s is not a valid name' % repr(for_clause.name))
+        items = mappend(self.expand_token, for_clause.items)
+        
+        status = 0    
+        for item in items:
+            self._env[for_clause.name] = item
+            for cmd in for_clause.cmds:
+                status = self.execute(cmd, redirs)
+        return status
+            
+    def _execute_and_or(self, or_and, redirs):
+        res = self.execute(or_and.left, redirs)        
+        if (or_and.op=='&&' and res==0) or (or_and.op!='&&' and res!=0):
+            res = self.execute(or_and.right, redirs)
+        return res
+            
+    def _execute_pipeline(self, pipeline, redirs):            
+        if len(pipeline.commands)==1:
+            status = self.execute(pipeline.commands[0], redirs)
+        else:
+            # Execute all commands one after the other
+            status = 0
+            inpath, outpath = None, None
+            try:
+                # Commands inputs and outputs cannot really be plugged as done
+                # by a real shell. Run commands sequentially and chain their
+                # input/output throught temporary files.
+                tmpfd, inpath = tempfile.mkstemp()
+                os.close(tmpfd)
+                tmpfd, outpath = tempfile.mkstemp()
+                os.close(tmpfd)
+                
+                inpath = win32_to_unix_path(inpath)
+                outpath = win32_to_unix_path(outpath)
+                
+                for i, cmd in enumerate(pipeline.commands):
+                    call_redirs = redirs.clone()
+                    try:
+                        if i!=0:
+                            call_redirs.add(self, '<', inpath)
+                        if i!=len(pipeline.commands)-1:
+                            call_redirs.add(self, '>', outpath)
+                        
+                        status = self.execute(cmd, call_redirs)
+                        
+                        # Chain inputs/outputs
+                        inpath, outpath = outpath, inpath
+                    finally:
+                        call_redirs.close()            
+            finally:
+                if inpath: os.remove(inpath)
+                if outpath: os.remove(outpath)
+        
+        if pipeline.reverse_status:
+            status = int(not status)
+        self._env['?'] = status
+        return status
+        
+    def _execute_function(self, name, args, interp, env, stdin, stdout, stderr, *others):
+        assert interp is self
+        
+        func = env.get_function(name)
+        #Set positional parameters
+        prevargs = None
+        try:
+            prevargs = env.set_positional_args(args)
+            try:
+                redirs = Redirections(stdin.dup(), stdout.dup(), stderr.dup())
+                try:
+                    status = self.execute(func, redirs)
+                finally:
+                    redirs.close()
+            except ReturnSignal as e:
+                status = int(e.args[0])
+                env['?'] = status
+            return status
+        finally:
+            #Reset positional parameters
+            if prevargs is not None:
+                env.set_positional_args(prevargs)
+                
+    def _execute_simple_command(self, token, redirs):
+        """Can raise ReturnSignal when return builtin is called, ExitSignal when
+        exit is called, and other shell exceptions upon builtin failures.
+        """
+        debug_command = 'debug-cmd' in self._debugflags
+        if debug_command:
+            self.log('word' + repr(token.words) + '\n')
+            self.log('assigns' + repr(token.assigns) + '\n')
+            self.log('redirs' + repr(token.redirs) + '\n')
+        
+        is_special = None
+        env = self._env
+        
+        try:
+            # Word expansion
+            args = []
+            for word in token.words:                
+                args += self.expand_token(word)
+                if is_special is None and args:
+                    is_special = env.is_function(args[0]) or \
+                        (args[0] in self.COMMANDS and self.COMMANDS[args[0]].is_special)
+                        
+            if debug_command:
+                self.log('_execute_simple_command' + str(args) + '\n')
+                
+            if not args:
+                # Redirections happen is a subshell
+                redirs = redirs.clone()
+            elif not is_special:
+                env = self._env.clone()
+            
+            # Redirections
+            self.redirect(redirs, token.redirs)
+                
+            # Variables assignments
+            res = 0
+            for type,(k,v) in token.assigns:
+                status, expanded = self.expand_variable((k,v))
+                if status is not None:
+                    res = status
+                if args:
+                    env.export(k, expanded)
+                else:
+                    env[k] = expanded
+                
+            if args and args[0] in ('.', 'source'):
+                res = self.dotcommand(env, args[1:])
+            elif args:
+                if args[0] in self.COMMANDS:
+                    command = self.COMMANDS[args[0]]
+                elif env.is_function(args[0]):
+                    command = Utility(self._execute_function, is_special=True)
+                else:
+                    if not '/' in args[0].replace('\\', '/'):
+                        cmd = env.find_in_path(args[0])
+                        if not cmd:
+                            # TODO: test error code on unknown command => 127
+                            raise CommandNotFound('Unknown command: "%s"' % args[0])
+                    else:
+                        # Handle commands like '/cygdrive/c/foo.bat'
+                        cmd = cygwin_to_windows_path(args[0])
+                        if not os.path.exists(cmd):
+                            raise CommandNotFound('%s: No such file or directory' % args[0])
+                        shebang = resolve_shebang(cmd)
+                        if shebang:
+                            cmd = shebang
+                        else:
+                            cmd = [cmd]
+                    args[0:1] = cmd
+                    command = Utility(builtin.run_command)
+                
+                # Command execution
+                if 'debug-cmd' in self._debugflags:
+                    self.log('redirections ' + str(redirs) + '\n')
+                    
+                res = command.func(args[0], args[1:], self, env,
+                                   redirs.stdin(), redirs.stdout(), 
+                                   redirs.stderr(), self._debugflags)
+            
+            if self._env.has_opt('-x'):
+                # Trace command execution in shell environment
+                # BUG: would be hard to reproduce a real shell behaviour since
+                # the AST is not annotated with source lines/tokens.
+                self._redirs.stdout().write(' '.join(args))
+                
+        except ReturnSignal:
+            raise
+        except ShellError as e:
+            if is_special or isinstance(e, (ExitSignal,
+                                            ShellSyntaxError, ExpansionError)):
+                raise e
+            self._redirs.stderr().write(str(e)+'\n')
+            return 1
+
+        return res
+
+    def expand_token(self, word):
+        """Expand a word as specified in [2.6 Word Expansions]. Return the list
+        of expanded words.
+        """
+        status, wtrees = self._expand_word(word)
+        return map(pyshlex.wordtree_as_string, wtrees)
+        
+    def expand_variable(self, word):
+        """Return a status code (or None if no command expansion occurred)
+        and a single word.
+        """
+        status, wtrees = self._expand_word(word, pathname=False, split=False)
+        words = map(pyshlex.wordtree_as_string, wtrees)
+        assert len(words)==1
+        return status, words[0]
+        
+    def expand_here_document(self, word):
+        """Return the expanded document as a single word. The here document is 
+        assumed to be unquoted.
+        """
+        status, wtrees = self._expand_word(word, pathname=False,
+                                           split=False, here_document=True)
+        words = map(pyshlex.wordtree_as_string, wtrees)
+        assert len(words)==1
+        return words[0]
+        
+    def expand_redirection(self, word):
+        """Return a single word."""
+        return self.expand_variable(word)[1]
+        
+    def get_env(self):
+        return self._env
+        
+    def _expand_word(self, token, pathname=True, split=True, here_document=False):
+        wtree = pyshlex.make_wordtree(token[1], here_document=here_document)
+        
+        # TODO: implement tilde expansion
+        def expand(wtree):
+            """Return a pseudo wordtree: the tree or its subelements can be empty
+            lists when no value result from the expansion.
+            """
+            status = None
+            for part in wtree:
+                if not isinstance(part, list):
+                    continue
+                if part[0]in ("'", '\\'):
+                    continue
+                elif part[0] in ('`', '$('):
+                    status, result = self._expand_command(part)
+                    part[:] = result
+                elif part[0] in ('$', '${'):
+                    part[:] = self._expand_parameter(part, wtree[0]=='"', split)
+                elif part[0] in ('', '"'):
+                    status, result = expand(part)
+                    part[:] = result
+                else:
+                    raise NotImplementedError('%s expansion is not implemented'
+                                              % part[0])
+            # [] is returned when an expansion result in no-field,
+            # like an empty $@
+            wtree = [p for p in wtree if p != []]
+            if len(wtree) < 3:
+                return status, []
+            return status, wtree
+        
+        status, wtree = expand(wtree)
+        if len(wtree) == 0:
+            return status, wtree
+        wtree = pyshlex.normalize_wordtree(wtree)
+        
+        if split:
+            wtrees = self._split_fields(wtree)
+        else:
+            wtrees = [wtree]
+        
+        if pathname:
+            wtrees = mappend(self._expand_pathname, wtrees)
+        
+        wtrees = map(self._remove_quotes, wtrees)
+        return status, wtrees
+        
+    def _expand_command(self, wtree):
+        # BUG: there is something to do with backslashes and quoted
+        # characters here
+        command = pyshlex.wordtree_as_string(wtree[1:-1])
+        status, output = self.subshell_output(command)
+        return status, ['', output, '']
+        
+    def _expand_parameter(self, wtree, quoted=False, split=False):
+        """Return a valid wtree or an empty list when no parameter results."""
+        # Get the parameter name
+        # TODO: implement weird expansion rules with ':'
+        name = pyshlex.wordtree_as_string(wtree[1:-1])
+        if not is_name(name) and not is_special_param(name):
+            raise ExpansionError('Bad substitution "%s"' % name)
+        # TODO: implement special parameters
+        if name in ('@', '*'):
+            args = self._env.get_positional_args()
+            if len(args) == 0:
+                return []
+            if len(args)<2:
+                return ['', ''.join(args), '']
+                
+            sep = self._env.get('IFS', '')[:1]
+            if split and quoted and name=='@':
+                # Introduce a new token to tell the caller that these parameters
+                # cause a split as specified in 2.5.2
+                return ['@'] + args + ['']
+            else:
+                return ['', sep.join(args), '']                
+        
+        return ['', self._env.get(name, ''), '']
+        
+    def _split_fields(self, wtree):
+        def is_empty(split):
+            return split==['', '', '']
+            
+        def split_positional(quoted):
+            # Return a list of wtree split according positional parameters rules.
+            # All remaining '@' groups are removed.
+            assert quoted[0]=='"'
+            
+            splits = [[]]
+            for part in quoted:
+                if not isinstance(part, list) or part[0]!='@':
+                    splits[-1].append(part)
+                else:
+                    # Empty or single argument list were dealt with already
+                    assert len(part)>3
+                    # First argument must join with the beginning part of the original word
+                    splits[-1].append(part[1])
+                    # Create double-quotes expressions for every argument after the first
+                    for arg in part[2:-1]:
+                        splits[-1].append('"')
+                        splits.append(['"', arg])
+            return splits
+        
+        # At this point, all expansions but pathnames have occured. Only quoted
+        # and positional sequences remain. Thus, all candidates for field splitting 
+        # are in the tree root, or are positional splits ('@') and lie in root
+        # children.
+        if not wtree or wtree[0] not in ('', '"'):
+            # The whole token is quoted or empty, nothing to split
+            return [wtree]
+            
+        if wtree[0]=='"':
+            wtree = ['', wtree, '']
+        
+        result = [['', '']]
+        for part in wtree[1:-1]:
+            if isinstance(part, list):
+                if part[0]=='"':
+                    splits = split_positional(part)
+                    if len(splits)<=1:
+                        result[-1] += [part, '']
+                    else:
+                        # Terminate the current split
+                        result[-1] += [splits[0], '']
+                        result += splits[1:-1]
+                        # Create a new split
+                        result += [['', splits[-1], '']]
+                else:
+                    result[-1] += [part, '']
+            else:
+                splits = self._env.split_fields(part)
+                if len(splits)<=1:
+                    # No split
+                    result[-1][-1] += part
+                else:
+                    # Terminate the current resulting part and create a new one
+                    result[-1][-1] += splits[0]
+                    result[-1].append('')
+                    result += [['', r, ''] for r in splits[1:-1]]
+                    result += [['', splits[-1]]]
+        result[-1].append('')
+        
+        # Leading and trailing empty groups come from leading/trailing blanks
+        if result and is_empty(result[-1]):
+            result[-1:] = []
+        if result and is_empty(result[0]):
+            result[:1] = []
+        return result
+        
+    def _expand_pathname(self, wtree):
+        """See [2.6.6 Pathname Expansion]."""
+        if self._env.has_opt('-f'):
+            return [wtree]
+        
+        # All expansions have been performed, only quoted sequences should remain
+        # in the tree. Generate the pattern by folding the tree, escaping special
+        # characters when appear quoted
+        special_chars = '*?[]'
+        
+        def make_pattern(wtree):
+            subpattern = []
+            for part in wtree[1:-1]:
+                if isinstance(part, list):
+                    part = make_pattern(part)
+                elif wtree[0]!='':
+                    for c in part:
+                        # Meta-characters cannot be quoted
+                        if c in special_chars:
+                            raise GlobError()
+                subpattern.append(part)
+            return ''.join(subpattern)
+            
+        def pwd_glob(pattern):
+            cwd = os.getcwd()
+            os.chdir(self._env['PWD'])
+            try:
+                return glob.glob(pattern) 
+            finally:
+                os.chdir(cwd)    
+            
+        #TODO: check working directory issues here wrt relative patterns
+        try:
+            pattern = make_pattern(wtree)
+            paths = pwd_glob(pattern)
+        except GlobError:
+            # BUG: Meta-characters were found in quoted sequences. The should 
+            # have been used literally but this is unsupported in current glob module.
+            # Instead we consider the whole tree must be used literally and
+            # therefore there is no point in globbing. This is wrong when meta
+            # characters are mixed with quoted meta in the same pattern like:
+            # < foo*"py*" >
+            paths = []
+            
+        if not paths:
+            return [wtree]
+        return [['', path, ''] for path in paths]
+        
+    def _remove_quotes(self, wtree):
+        """See [2.6.7 Quote Removal]."""
+        
+        def unquote(wtree):
+            unquoted = []
+            for part in wtree[1:-1]:
+                if isinstance(part, list):
+                    part = unquote(part)
+                unquoted.append(part)
+            return ''.join(unquoted)
+            
+        return ['', unquote(wtree), '']
+        
+    def subshell(self, script=None, ast=None, redirs=None):
+        """Execute the script or AST in a subshell, with inherited redirections
+        if redirs is not None.
+        """
+        if redirs:
+            sub_redirs = redirs
+        else:
+            sub_redirs = redirs.clone()
+        
+        subshell = None    
+        try:
+            subshell = Interpreter(None, self._debugflags, self._env.clone(True),
+                                   sub_redirs, opts=self._options)
+            return subshell.execute_script(script, ast)
+        finally:
+            if not redirs: sub_redirs.close()
+            if subshell: subshell.close()
+        
+    def subshell_output(self, script):
+        """Execute the script in a subshell and return the captured output."""        
+        # Create temporary file to capture subshell output
+        tmpfd, tmppath = tempfile.mkstemp()
+        try:
+            tmpfile = os.fdopen(tmpfd, 'wb')
+            stdout = FileWrapper('w', tmpfile)
+            
+            redirs = Redirections(self._redirs.stdin().dup(),
+                                  stdout,
+                                  self._redirs.stderr().dup())            
+            try:
+                status = self.subshell(script=script, redirs=redirs)
+            finally:
+                redirs.close()
+                redirs = None
+            
+            # Extract subshell standard output
+            tmpfile = open(tmppath, 'rb')
+            try:
+                output = tmpfile.read()
+                return status, output.rstrip('\n')
+            finally:
+                tmpfile.close()
+        finally:
+            os.remove(tmppath)
+
+    def _asynclist(self, cmd):
+        args = (self._env.get_variables(), cmd)
+        arg = encodeargs(args)
+        assert len(args) < 30*1024
+        cmd = ['pysh.bat', '--ast', '-c', arg]
+        p = subprocess.Popen(cmd, cwd=self._env['PWD'])
+        self._children[p.pid] = p
+        self._env['!'] = p.pid
+        return 0
+
+    def wait(self, pids=None):
+        if not pids:
+            pids = self._children.keys()
+
+        status = 127
+        for pid in pids:
+            if pid not in self._children:
+                continue
+            p = self._children.pop(pid)
+            status = p.wait()
+
+        return status
+