diff --git a/bitbake/lib/bb/pysh/pyshyacc.py b/bitbake/lib/bb/pysh/pyshyacc.py
new file mode 100644
index 0000000..e8e80aa
--- /dev/null
+++ b/bitbake/lib/bb/pysh/pyshyacc.py
@@ -0,0 +1,779 @@
+# pyshyacc.py - PLY grammar definition 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.
+
+"""PLY grammar file.
+"""
+import os.path
+import sys
+
+import pyshlex
+tokens = pyshlex.tokens
+
+from ply import yacc
+import sherrors
+    
+class IORedirect:
+    def __init__(self, op, filename, io_number=None):
+        self.op = op
+        self.filename = filename
+        self.io_number = io_number
+        
+class HereDocument:
+    def __init__(self, op, name, content, io_number=None):
+        self.op = op
+        self.name = name
+        self.content = content
+        self.io_number = io_number
+
+def make_io_redirect(p):
+    """Make an IORedirect instance from the input 'io_redirect' production."""
+    name, io_number, io_target = p
+    assert name=='io_redirect'
+    
+    if io_target[0]=='io_file':
+        io_type, io_op, io_file = io_target
+        return IORedirect(io_op, io_file, io_number)
+    elif io_target[0]=='io_here':
+        io_type, io_op, io_name, io_content = io_target
+        return HereDocument(io_op, io_name, io_content, io_number)
+    else:
+        assert False, "Invalid IO redirection token %s" % repr(io_type)
+        
+class SimpleCommand:
+    """
+    assigns contains (name, value) pairs.
+    """
+    def __init__(self, words, redirs, assigns):
+        self.words = list(words)
+        self.redirs = list(redirs)
+        self.assigns = list(assigns)
+
+class Pipeline:
+    def __init__(self, commands, reverse_status=False):
+        self.commands = list(commands)
+        assert self.commands    #Grammar forbids this
+        self.reverse_status = reverse_status
+        
+class AndOr:
+    def __init__(self, op, left, right):
+        self.op = str(op)
+        self.left = left
+        self.right = right
+        
+class ForLoop:
+    def __init__(self, name, items, cmds):
+        self.name = str(name)
+        self.items = list(items)
+        self.cmds = list(cmds)
+        
+class WhileLoop:
+    def __init__(self, condition, cmds):
+        self.condition = list(condition)
+        self.cmds = list(cmds)
+        
+class UntilLoop:
+    def __init__(self, condition, cmds):
+        self.condition = list(condition)
+        self.cmds = list(cmds)
+
+class FunDef:
+    def __init__(self, name, body):
+        self.name = str(name)
+        self.body = body
+        
+class BraceGroup:
+    def __init__(self, cmds):
+        self.cmds = list(cmds)
+        
+class IfCond:
+    def __init__(self, cond, if_cmds, else_cmds):
+        self.cond = list(cond)
+        self.if_cmds = if_cmds
+        self.else_cmds = else_cmds
+
+class Case:
+    def __init__(self, name, items):
+        self.name = name
+        self.items = items
+        
+class SubShell:
+    def __init__(self, cmds):
+        self.cmds = cmds
+
+class RedirectList:
+    def __init__(self, cmd, redirs):
+        self.cmd = cmd
+        self.redirs = list(redirs)
+        
+def get_production(productions, ptype):
+    """productions must be a list of production tuples like (name, obj) where
+    name is the production string identifier.
+    Return the first production named 'ptype'. Raise KeyError if None can be
+    found.
+    """
+    for production in productions:
+        if production is not None and production[0]==ptype:
+            return production
+    raise KeyError(ptype)
+    
+#-------------------------------------------------------------------------------
+# PLY grammar definition
+#-------------------------------------------------------------------------------
+
+def p_multiple_commands(p):
+    """multiple_commands : newline_sequence
+                         | complete_command
+                         | multiple_commands complete_command"""
+    if len(p)==2:
+        if p[1] is not None:
+            p[0] = [p[1]]
+        else:
+            p[0] = []
+    else:
+        p[0] = p[1] + [p[2]]
+
+def p_complete_command(p):
+    """complete_command : list separator
+                        | list"""
+    if len(p)==3 and p[2] and p[2][1] == '&':
+        p[0] = ('async', p[1])
+    else:
+        p[0] = p[1]
+                 
+def p_list(p):
+    """list : list separator_op and_or
+            |                   and_or"""
+    if len(p)==2:
+        p[0] = [p[1]]
+    else:
+        #if p[2]!=';':
+        #    raise NotImplementedError('AND-OR list asynchronous execution is not implemented')
+        p[0] = p[1] + [p[3]]
+       
+def p_and_or(p):
+    """and_or : pipeline
+              | and_or AND_IF linebreak pipeline
+              | and_or OR_IF  linebreak pipeline"""
+    if len(p)==2:
+        p[0] = p[1]
+    else:
+        p[0] = ('and_or', AndOr(p[2], p[1], p[4]))
+        
+def p_maybe_bang_word(p):
+    """maybe_bang_word : Bang"""
+    p[0] = ('maybe_bang_word', p[1])
+            
+def p_pipeline(p):
+    """pipeline : pipe_sequence
+                | bang_word pipe_sequence"""
+    if len(p)==3:
+        p[0] = ('pipeline', Pipeline(p[2][1:], True))
+    else:
+        p[0] = ('pipeline', Pipeline(p[1][1:]))
+
+def p_pipe_sequence(p):
+    """pipe_sequence : command
+                     | pipe_sequence PIPE linebreak command"""
+    if len(p)==2:
+        p[0] = ['pipe_sequence', p[1]]
+    else:
+        p[0] = p[1] + [p[4]]
+
+def p_command(p):
+    """command : simple_command
+               | compound_command
+               | compound_command redirect_list
+               | function_definition"""
+        
+    if p[1][0] in ( 'simple_command', 
+                    'for_clause',
+                    'while_clause',
+                    'until_clause',
+                    'case_clause',
+                    'if_clause',
+                    'function_definition',
+                    'subshell',
+                    'brace_group',):
+        if len(p) == 2:
+            p[0] = p[1]
+        else:
+            p[0] = ('redirect_list', RedirectList(p[1], p[2][1:]))
+    else:
+        raise NotImplementedError('%s command is not implemented' % repr(p[1][0]))
+
+def p_compound_command(p):
+    """compound_command : brace_group
+                        | subshell
+                        | for_clause
+                        | case_clause
+                        | if_clause
+                        | while_clause
+                        | until_clause"""
+    p[0] = p[1]
+
+def p_subshell(p):
+    """subshell : LPARENS compound_list RPARENS"""
+    p[0] = ('subshell', SubShell(p[2][1:]))
+
+def p_compound_list(p):
+    """compound_list : term
+                     | newline_list term
+                     |              term separator
+                     | newline_list term separator"""
+    productions = p[1:]           
+    try:
+        sep = get_production(productions, 'separator')
+        if sep[1]!=';':
+            raise NotImplementedError()
+    except KeyError:
+        pass
+    term = get_production(productions, 'term')
+    p[0] = ['compound_list'] + term[1:]
+
+def p_term(p):
+    """term : term separator and_or
+            |                and_or"""
+    if len(p)==2:
+        p[0] = ['term', p[1]]
+    else:
+        if p[2] is not None and p[2][1] == '&':
+            p[0] = ['term', ('async', p[1][1:])] + [p[3]]
+        else:
+            p[0] = p[1] + [p[3]]
+            
+def p_maybe_for_word(p):
+    # Rearrange 'For' priority wrt TOKEN. See p_for_word
+    """maybe_for_word : For"""
+    p[0] = ('maybe_for_word', p[1])
+
+def p_for_clause(p):
+    """for_clause : for_word name linebreak                            do_group
+                  | for_word name linebreak in          sequential_sep do_group
+                  | for_word name linebreak in wordlist sequential_sep do_group"""
+    productions = p[1:]
+    do_group = get_production(productions, 'do_group')
+    try:
+        items = get_production(productions, 'in')[1:]
+    except KeyError:
+        raise NotImplementedError('"in" omission is not implemented')
+        
+    try:
+        items = get_production(productions, 'wordlist')[1:]
+    except KeyError:
+        items = []
+        
+    name = p[2]
+    p[0] = ('for_clause', ForLoop(name, items, do_group[1:]))
+
+def p_name(p):
+    """name : token""" #Was NAME instead of token
+    p[0] = p[1]
+
+def p_in(p):
+    """in : In"""
+    p[0] = ('in', p[1])
+
+def p_wordlist(p):
+    """wordlist : wordlist token
+                |          token"""
+    if len(p)==2:
+        p[0] = ['wordlist', ('TOKEN', p[1])]
+    else:
+        p[0] = p[1] + [('TOKEN', p[2])]
+
+def p_case_clause(p):
+    """case_clause : Case token linebreak in linebreak case_list    Esac
+                   | Case token linebreak in linebreak case_list_ns Esac
+                   | Case token linebreak in linebreak              Esac"""
+    if len(p) < 8:
+        items = []
+    else:
+        items = p[6][1:]
+    name = p[2]
+    p[0] = ('case_clause', Case(name, [c[1] for c in items]))
+       
+def p_case_list_ns(p):
+    """case_list_ns : case_list case_item_ns
+                    |           case_item_ns"""
+    p_case_list(p)
+      
+def p_case_list(p):
+    """case_list : case_list case_item
+                 |           case_item"""
+    if len(p)==2:
+        p[0] = ['case_list', p[1]]
+    else:
+        p[0] = p[1] + [p[2]]
+        
+def p_case_item_ns(p):
+    """case_item_ns :         pattern RPARENS               linebreak
+                    |         pattern RPARENS compound_list linebreak
+                    | LPARENS pattern RPARENS               linebreak
+                    | LPARENS pattern RPARENS compound_list linebreak"""
+    p_case_item(p)
+                 
+def p_case_item(p):
+    """case_item :         pattern RPARENS linebreak     DSEMI linebreak
+                 |         pattern RPARENS compound_list DSEMI linebreak
+                 | LPARENS pattern RPARENS linebreak     DSEMI linebreak
+                 | LPARENS pattern RPARENS compound_list DSEMI linebreak"""
+    if len(p) < 7:
+        name = p[1][1:]
+    else:
+        name = p[2][1:]
+
+    try:
+        cmds = get_production(p[1:], "compound_list")[1:]
+    except KeyError:
+        cmds = []
+
+    p[0] = ('case_item', (name, cmds))
+                 
+def p_pattern(p):
+    """pattern :              token
+               | pattern PIPE token"""
+    if len(p)==2:
+        p[0] = ['pattern', ('TOKEN', p[1])]
+    else:
+        p[0] = p[1] + [('TOKEN', p[2])]
+
+def p_maybe_if_word(p):
+    # Rearrange 'If' priority wrt TOKEN. See p_if_word
+    """maybe_if_word : If"""
+    p[0] = ('maybe_if_word', p[1])
+
+def p_maybe_then_word(p):
+    # Rearrange 'Then' priority wrt TOKEN. See p_then_word
+    """maybe_then_word : Then"""
+    p[0] = ('maybe_then_word', p[1])
+                 
+def p_if_clause(p):
+    """if_clause : if_word compound_list then_word compound_list else_part Fi
+                 | if_word compound_list then_word compound_list           Fi"""
+    else_part = []
+    if len(p)==7:
+        else_part = p[5]
+    p[0] = ('if_clause', IfCond(p[2][1:], p[4][1:], else_part))
+                 
+def p_else_part(p):
+    """else_part : Elif compound_list then_word compound_list else_part
+                 | Elif compound_list then_word compound_list
+                 | Else compound_list"""
+    if len(p)==3:
+        p[0] = p[2][1:]
+    else:
+        else_part = []
+        if len(p)==6:
+            else_part = p[5]
+        p[0] = ('elif', IfCond(p[2][1:], p[4][1:], else_part))
+                 
+def p_while_clause(p):
+    """while_clause : While compound_list do_group"""
+    p[0] = ('while_clause', WhileLoop(p[2][1:], p[3][1:]))
+    
+def p_maybe_until_word(p):
+    # Rearrange 'Until' priority wrt TOKEN. See p_until_word
+    """maybe_until_word : Until"""
+    p[0] = ('maybe_until_word', p[1])
+           
+def p_until_clause(p):
+    """until_clause : until_word compound_list do_group"""
+    p[0] = ('until_clause', UntilLoop(p[2][1:], p[3][1:]))
+                 
+def p_function_definition(p):
+    """function_definition : fname LPARENS RPARENS linebreak function_body"""
+    p[0] = ('function_definition', FunDef(p[1], p[5]))
+                 
+def p_function_body(p):
+    """function_body : compound_command
+                     | compound_command redirect_list"""
+    if len(p)!=2:
+        raise NotImplementedError('functions redirections lists are not implemented')    
+    p[0] = p[1]    
+
+def p_fname(p):
+    """fname : TOKEN""" #Was NAME instead of token
+    p[0] = p[1]
+
+def p_brace_group(p):
+    """brace_group : Lbrace compound_list Rbrace"""
+    p[0] = ('brace_group', BraceGroup(p[2][1:]))
+
+def p_maybe_done_word(p):
+    #See p_assignment_word for details.
+    """maybe_done_word : Done"""
+    p[0] = ('maybe_done_word', p[1])
+
+def p_maybe_do_word(p):
+    """maybe_do_word : Do"""
+    p[0] = ('maybe_do_word', p[1])
+
+def p_do_group(p):
+    """do_group : do_word compound_list done_word"""
+    #Do group contains a list of AndOr
+    p[0] = ['do_group'] + p[2][1:]
+
+def p_simple_command(p):
+    """simple_command : cmd_prefix cmd_word cmd_suffix
+                      | cmd_prefix cmd_word
+                      | cmd_prefix
+                      | cmd_name cmd_suffix
+                      | cmd_name"""
+    words, redirs, assigns = [], [], []
+    for e in p[1:]:
+        name = e[0]
+        if name in ('cmd_prefix', 'cmd_suffix'):
+            for sube in e[1:]:
+                subname = sube[0]
+                if subname=='io_redirect':
+                    redirs.append(make_io_redirect(sube))
+                elif subname=='ASSIGNMENT_WORD':
+                    assigns.append(sube)
+                else:
+                    words.append(sube)
+        elif name in ('cmd_word', 'cmd_name'):
+            words.append(e)
+            
+    cmd = SimpleCommand(words, redirs, assigns)
+    p[0] = ('simple_command', cmd)
+
+def p_cmd_name(p):
+    """cmd_name : TOKEN"""
+    p[0] = ('cmd_name', p[1])
+    
+def p_cmd_word(p):
+    """cmd_word : token"""
+    p[0] = ('cmd_word', p[1])
+
+def p_maybe_assignment_word(p):
+    #See p_assignment_word for details.
+    """maybe_assignment_word : ASSIGNMENT_WORD"""
+    p[0] = ('maybe_assignment_word', p[1])
+    
+def p_cmd_prefix(p):
+    """cmd_prefix :            io_redirect
+                  | cmd_prefix io_redirect
+                  |            assignment_word
+                  | cmd_prefix assignment_word"""
+    try:
+        prefix = get_production(p[1:], 'cmd_prefix')
+    except KeyError:
+        prefix = ['cmd_prefix']
+        
+    try:
+        value = get_production(p[1:], 'assignment_word')[1]
+        value = ('ASSIGNMENT_WORD', value.split('=', 1))
+    except KeyError:        
+        value = get_production(p[1:], 'io_redirect')
+    p[0] = prefix + [value]
+                                  
+def p_cmd_suffix(p):
+    """cmd_suffix   :            io_redirect
+                    | cmd_suffix io_redirect
+                    |            token
+                    | cmd_suffix token
+                    |            maybe_for_word
+                    | cmd_suffix maybe_for_word
+                    |            maybe_done_word
+                    | cmd_suffix maybe_done_word
+                    |            maybe_do_word
+                    | cmd_suffix maybe_do_word
+                    |            maybe_until_word
+                    | cmd_suffix maybe_until_word
+                    |            maybe_assignment_word
+                    | cmd_suffix maybe_assignment_word
+                    |            maybe_if_word
+                    | cmd_suffix maybe_if_word
+                    |            maybe_then_word
+                    | cmd_suffix maybe_then_word
+                    |            maybe_bang_word
+                    | cmd_suffix maybe_bang_word"""
+    try:
+        suffix = get_production(p[1:], 'cmd_suffix')
+        token = p[2]
+    except KeyError:
+        suffix = ['cmd_suffix']
+        token = p[1]
+        
+    if isinstance(token, tuple):
+        if token[0]=='io_redirect':
+            p[0] = suffix + [token]
+        else:
+            #Convert maybe_*  to TOKEN if necessary
+            p[0] = suffix + [('TOKEN', token[1])]
+    else:
+        p[0] = suffix + [('TOKEN', token)]
+                 
+def p_redirect_list(p):
+    """redirect_list : io_redirect
+                     | redirect_list io_redirect"""
+    if len(p) == 2:
+        p[0] = ['redirect_list', make_io_redirect(p[1])]
+    else:
+        p[0] = p[1] + [make_io_redirect(p[2])]
+    
+def p_io_redirect(p):
+    """io_redirect :           io_file
+                   | IO_NUMBER io_file
+                   |           io_here
+                   | IO_NUMBER io_here"""
+    if len(p)==3:
+        p[0] = ('io_redirect', p[1], p[2])
+    else:
+        p[0] = ('io_redirect', None, p[1])
+    
+def p_io_file(p):
+    #Return the tuple (operator, filename)
+    """io_file : LESS      filename
+               | LESSAND   filename
+               | GREATER   filename
+               | GREATAND  filename
+               | DGREAT    filename
+               | LESSGREAT filename
+               | CLOBBER   filename"""
+    #Extract the filename from the file
+    p[0] = ('io_file', p[1], p[2][1])
+
+def p_filename(p):
+    #Return the filename
+    """filename : TOKEN"""
+    p[0] = ('filename', p[1])
+        
+def p_io_here(p):
+    """io_here : DLESS here_end
+               | DLESSDASH here_end"""
+    p[0] = ('io_here', p[1], p[2][1], p[2][2])
+
+def p_here_end(p):
+    """here_end : HERENAME TOKEN"""
+    p[0] = ('here_document', p[1], p[2])
+    
+def p_newline_sequence(p):
+    # Nothing in the grammar can handle leading NEWLINE productions, so add
+    # this one with the lowest possible priority relatively to newline_list.
+    """newline_sequence : newline_list"""
+    p[0] = None
+    
+def p_newline_list(p):
+    """newline_list : NEWLINE
+                    | newline_list NEWLINE"""
+    p[0] = None
+                    
+def p_linebreak(p):
+    """linebreak : newline_list
+                 | empty"""
+    p[0] = None
+
+def p_separator_op(p):                 
+    """separator_op : COMMA
+                    | AMP"""
+    p[0] = p[1]
+
+def p_separator(p):
+    """separator : separator_op linebreak
+                 | newline_list"""
+    if len(p)==2:
+        #Ignore newlines
+        p[0] = None
+    else:
+        #Keep the separator operator
+        p[0] = ('separator', p[1])
+                 
+def p_sequential_sep(p):
+    """sequential_sep : COMMA linebreak
+                      | newline_list"""
+    p[0] = None
+
+# Low priority TOKEN => for_word conversion.
+# Let maybe_for_word be used as a token when necessary in higher priority
+# rules. 
+def p_for_word(p):
+    """for_word : maybe_for_word"""
+    p[0] = p[1]
+
+def p_if_word(p):
+    """if_word : maybe_if_word"""
+    p[0] = p[1]
+
+def p_then_word(p):
+    """then_word : maybe_then_word"""
+    p[0] = p[1]
+
+def p_done_word(p):
+    """done_word : maybe_done_word"""
+    p[0] = p[1]
+
+def p_do_word(p):
+    """do_word : maybe_do_word"""
+    p[0] = p[1]
+    
+def p_until_word(p):
+    """until_word : maybe_until_word"""
+    p[0] = p[1]
+    
+def p_assignment_word(p):
+    """assignment_word : maybe_assignment_word"""
+    p[0] = ('assignment_word', p[1][1])
+    
+def p_bang_word(p):
+    """bang_word : maybe_bang_word"""
+    p[0] = ('bang_word', p[1][1])
+
+def p_token(p):
+    """token : TOKEN
+             | Fi"""
+    p[0] = p[1]
+
+def p_empty(p):
+    'empty :'
+    p[0] = None
+    
+# Error rule for syntax errors
+def p_error(p):
+    msg = []
+    w = msg.append
+    w('%r\n' % p)
+    w('followed by:\n')
+    for i in range(5):
+        n = yacc.token()
+        if not n:
+            break
+        w('  %r\n' % n)
+    raise sherrors.ShellSyntaxError(''.join(msg))
+
+# Build the parser
+try:
+    import pyshtables
+except ImportError:
+    outputdir = os.path.dirname(__file__)
+    if not os.access(outputdir, os.W_OK):
+        outputdir = ''
+    yacc.yacc(tabmodule = 'pyshtables', outputdir = outputdir, debug = 0)
+else:
+    yacc.yacc(tabmodule = 'pysh.pyshtables', write_tables = 0, debug = 0)
+
+
+def parse(input, eof=False, debug=False):
+    """Parse a whole script at once and return the generated AST and unconsumed
+    data in a tuple.
+    
+    NOTE: eof is probably meaningless for now, the parser being unable to work
+    in pull mode. It should be set to True.
+    """
+    lexer = pyshlex.PLYLexer()
+    remaining = lexer.add(input, eof)
+    if lexer.is_empty():
+        return [], remaining
+    if debug:
+        debug = 2
+    return yacc.parse(lexer=lexer, debug=debug), remaining
+
+#-------------------------------------------------------------------------------
+# AST rendering helpers
+#-------------------------------------------------------------------------------    
+
+def format_commands(v):
+    """Return a tree made of strings and lists. Make command trees easier to
+    display.
+    """
+    if isinstance(v, list):
+        return [format_commands(c) for c in v]
+    if isinstance(v, tuple):
+        if len(v)==2 and isinstance(v[0], str) and not isinstance(v[1], str):
+            if v[0] == 'async':
+                return ['AsyncList', map(format_commands, v[1])]
+            else:
+                #Avoid decomposing tuples like ('pipeline', Pipeline(...))
+                return format_commands(v[1])
+        return format_commands(list(v))
+    elif isinstance(v, IfCond):
+        name = ['IfCond']
+        name += ['if', map(format_commands, v.cond)]
+        name += ['then', map(format_commands, v.if_cmds)]
+        name += ['else', map(format_commands, v.else_cmds)]
+        return name
+    elif isinstance(v, ForLoop):
+        name = ['ForLoop']
+        name += [repr(v.name)+' in ', map(str, v.items)]
+        name += ['commands', map(format_commands, v.cmds)]
+        return name
+    elif isinstance(v, AndOr):
+        return [v.op, format_commands(v.left), format_commands(v.right)]
+    elif isinstance(v, Pipeline):
+        name = 'Pipeline'
+        if v.reverse_status:
+            name = '!' + name
+        return [name, format_commands(v.commands)]
+    elif isinstance(v, Case):
+        name = ['Case']
+        name += [v.name, format_commands(v.items)]
+    elif isinstance(v, SimpleCommand):
+        name = ['SimpleCommand']
+        if v.words:                
+            name += ['words', map(str, v.words)]
+        if v.assigns:
+            assigns = [tuple(a[1]) for a in v.assigns]
+            name += ['assigns', map(str, assigns)]
+        if v.redirs:
+            name += ['redirs', map(format_commands, v.redirs)]
+        return name
+    elif isinstance(v, RedirectList):
+        name = ['RedirectList']
+        if v.redirs:
+            name += ['redirs', map(format_commands, v.redirs)]
+        name += ['command', format_commands(v.cmd)]
+        return name
+    elif isinstance(v, IORedirect):
+        return ' '.join(map(str, (v.io_number, v.op, v.filename)))
+    elif isinstance(v, HereDocument):
+        return ' '.join(map(str, (v.io_number, v.op, repr(v.name), repr(v.content))))
+    elif isinstance(v, SubShell):
+        return ['SubShell', map(format_commands, v.cmds)]
+    else:
+        return repr(v)
+             
+def print_commands(cmds, output=sys.stdout):
+    """Pretty print a command tree."""
+    def print_tree(cmd, spaces, output):
+        if isinstance(cmd, list):
+            for c in cmd:
+                print_tree(c, spaces + 3, output)              
+        else:
+            print >>output, ' '*spaces + str(cmd)
+    
+    formatted = format_commands(cmds)
+    print_tree(formatted, 0, output)
+    
+    
+def stringify_commands(cmds): 
+    """Serialize a command tree as a string.
+    
+    Returned string is not pretty and is currently used for unit tests only.
+    """   
+    def stringify(value):
+        output = []
+        if isinstance(value, list):
+            formatted = []
+            for v in value:
+                formatted.append(stringify(v))
+            formatted = ' '.join(formatted)
+            output.append(''.join(['<', formatted, '>']))
+        else:
+            output.append(value)
+        return ' '.join(output)
+            
+    return stringify(format_commands(cmds))
+    
+        
+def visit_commands(cmds, callable):
+    """Visit the command tree and execute callable on every Pipeline and 
+    SimpleCommand instances.
+    """
+    if isinstance(cmds, (tuple, list)):
+        map(lambda c: visit_commands(c,callable), cmds)
+    elif isinstance(cmds, (Pipeline, SimpleCommand)):
+        callable(cmds)