Feat(rc): added subshell commands and cd builtin

Slowly chipping away at a decent feature list.
Subshell commands are executed by @{ ... }.

9 files changed, 366 insertions, 235 deletions

diff --git a/sys/cmd/rc/code.c b/sys/cmd/rc/code.c
index 719e63b..38cc06a 100644
--- a/sys/cmd/rc/code.c
+++ b/sys/cmd/rc/code.c
@@ -110,6 +110,18 @@ walk(Tree *node)
         storepc(addr);
         break;
 
+    case Tsubshell:
+        emitf(Xsubshell);
+        addr = emiti(0);
+        walk(node->child[0]);
+        emitf(Xexit);
+        storepc(addr);
+        break;
+
+    case Tbang:
+        walk(node->child[0]);
+        emitf(Xbang);
+
     case Tword:
         emitf(Xword);
         emits(strdup(node->str));
diff --git a/sys/cmd/rc/exec.c b/sys/cmd/rc/exec.c
index 37c289b..217f7ee 100644
--- a/sys/cmd/rc/exec.c
+++ b/sys/cmd/rc/exec.c
@@ -17,6 +17,7 @@ static Word nullpath = { .str="", .link=nil };
 
 struct Builtin builtin[]={
     {".",     xdot},
+    {"cd",    xcd},
     {"fg",    xfg},
     {"jobs",  xjob},
     0,
@@ -326,7 +327,7 @@ xdot(void)
     Thread *old;
     char file[512];
 
-    popword();
+    popword(); // "."
 #if 0
     if(proc->args->word && strcmp(proc->args->word->str, "-i")==0){
         iflag = 1;
@@ -383,6 +384,49 @@ xdot(void)
 }
 
 void
+xcd(void)
+{
+    Word *arg;
+    Word *cdpath;
+    char dir[512];
+
+    popword(); // cd
+
+    arg = runner->args->word;
+    switch(count(arg)){
+    default:
+        print(shell.err, "usage: cd [directory]\n");
+        break;
+    case 0:
+        arg = var("home")->val;
+        if(count(arg) >= 1){
+            if(chdir(arg->str) < 0)
+                print(shell.err, "failed cd: %s\n", strerror(errno));
+        }else{
+            print(shell.err, "ambiguous cd: $home empty\n");
+        }
+        break;
+
+    case 1:
+        // TODO: add cdpath
+        cdpath = &nullpath;
+        for(; cdpath; cdpath = cdpath->link){
+            strcpy(dir, cdpath->str);
+            if(dir[0])
+                strcat(dir,"/");
+            strcat(dir, arg->str);
+            if(chdir(dir) < 0){
+                print(shell.err, "failed cd %s: %s\n", dir, strerror(errno));
+            }
+            break;
+        }
+        break;
+    }
+
+    poplist();
+}
+
+void
 xjob(void)
 {
     int i;
@@ -681,6 +725,37 @@ Xasync(void)
 }
 
 void
+Xsubshell(void)
+{
+    int pid;
+
+    switch(pid=fork()){
+    case -1:
+        Xerror("fork failed: try again");
+        break;
+
+    case 0: // child
+        clearwait(runner);
+        if(shell.interactive){ // NOTE: this needs to read off its caller's interactivity
+            setpid(getpid());
+            tcsetpgrp(0, runner->pgid);
+            defaultsignal();
+        }
+        run(runner->code.exe, runner->code.i+1, runner->local, 1);
+        runner->link = nil;
+        break;
+
+    default: // parent
+        setpid(pid);
+        addwait(runner, pid);
+        waitfor(runner, pid); // wait until child finishes
+        runner->code.i = runner->code.exe[runner->code.i].i; // jump to end of subshell command and continue execution
+    }
+}
+
+
+
+void
 Xbasic(void)
 {
     Var  *v;
@@ -781,6 +856,15 @@ Xflat(void)
 }
 
 void
+Xbang(void)
+{
+    if(runner->status)
+        runner->status = 0;
+    else
+        runner->status = 1;
+}
+
+void
 Xexit(void)
 {
     exit(runner->status);
diff --git a/sys/cmd/rc/exec.h b/sys/cmd/rc/exec.h
index 0df01d0..9ad0f3d 100644
--- a/sys/cmd/rc/exec.h
+++ b/sys/cmd/rc/exec.h
@@ -15,8 +15,10 @@ void Xlocal(void);
 void Xreadcmd(void);
 void Xunlocal(void);
 void Xassign(void);
+void Xbang(void);
 void Xasync(void);
-void Xbasic(void);  // Xbasic(args) run command and wait for result
+void Xbasic(void);     // Xbasic(args) run command and wait for result
+void Xsubshell(void);
 void Xword(void);
 void Xcount(void);
 void Xflat(void);
@@ -24,6 +26,7 @@ void Xflat(void);
 void Xerror(char*);
 
 /* builtin commands */
+void xcd(void);
 void xfg(void);
 void xdot(void);
 void xjob(void);
diff --git a/sys/cmd/rc/lex.c b/sys/cmd/rc/lex.c
index 06737ba..4325882 100644
--- a/sys/cmd/rc/lex.c
+++ b/sys/cmd/rc/lex.c
@@ -191,6 +191,14 @@ yylex(void)
         put1('&');
         return '&';
 
+    case '@':
+        put1('@');
+        return Tsubshell;
+
+    case '!':
+        put1('!');
+        return Tbang;
+
     case '$':
         if(nextis('#')){
             put2('$','#');
diff --git a/sys/cmd/rc/parse.c b/sys/cmd/rc/parse.c
index b88e8ab..c53f514 100644
--- a/sys/cmd/rc/parse.c
+++ b/sys/cmd/rc/parse.c
@@ -110,43 +110,44 @@ enum yysymbol_kind_t
   YYSYMBOL_Tif = 5,                        /* Tif  */
   YYSYMBOL_Telse = 6,                      /* Telse  */
   YYSYMBOL_Tbang = 7,                      /* Tbang  */
-  YYSYMBOL_Targs = 8,                      /* Targs  */
-  YYSYMBOL_Tindex = 9,                     /* Tindex  */
-  YYSYMBOL_Tbasic = 10,                    /* Tbasic  */
-  YYSYMBOL_Tparen = 11,                    /* Tparen  */
-  YYSYMBOL_Tblock = 12,                    /* Tblock  */
-  YYSYMBOL_Twhile = 13,                    /* Twhile  */
-  YYSYMBOL_14_n_ = 14,                     /* '\n'  */
-  YYSYMBOL_15_ = 15,                       /* '$'  */
-  YYSYMBOL_Tcount = 16,                    /* Tcount  */
-  YYSYMBOL_Tflat = 17,                     /* Tflat  */
-  YYSYMBOL_18_ = 18,                       /* '('  */
-  YYSYMBOL_19_ = 19,                       /* ')'  */
-  YYSYMBOL_20_ = 20,                       /* '{'  */
-  YYSYMBOL_21_ = 21,                       /* '}'  */
-  YYSYMBOL_22_ = 22,                       /* ';'  */
-  YYSYMBOL_23_ = 23,                       /* '&'  */
-  YYSYMBOL_24_ = 24,                       /* '='  */
-  YYSYMBOL_25_ = 25,                       /* '^'  */
-  YYSYMBOL_YYACCEPT = 26,                  /* $accept  */
-  YYSYMBOL_rc = 27,                        /* rc  */
-  YYSYMBOL_line = 28,                      /* line  */
-  YYSYMBOL_body = 29,                      /* body  */
-  YYSYMBOL_paren = 30,                     /* paren  */
-  YYSYMBOL_block = 31,                     /* block  */
-  YYSYMBOL_cmds = 32,                      /* cmds  */
-  YYSYMBOL_cmdsln = 33,                    /* cmdsln  */
-  YYSYMBOL_ifbody = 34,                    /* ifbody  */
-  YYSYMBOL_assign = 35,                    /* assign  */
-  YYSYMBOL_cmd = 36,                       /* cmd  */
-  YYSYMBOL_basic = 37,                     /* basic  */
-  YYSYMBOL_atom = 38,                      /* atom  */
-  YYSYMBOL_word = 39,                      /* word  */
-  YYSYMBOL_executable = 40,                /* executable  */
-  YYSYMBOL_nonkeyword = 41,                /* nonkeyword  */
-  YYSYMBOL_keyword = 42,                   /* keyword  */
-  YYSYMBOL_wordsnl = 43,                   /* wordsnl  */
-  YYSYMBOL_nl = 44                         /* nl  */
+  YYSYMBOL_Tsubshell = 8,                  /* Tsubshell  */
+  YYSYMBOL_Targs = 9,                      /* Targs  */
+  YYSYMBOL_Tindex = 10,                    /* Tindex  */
+  YYSYMBOL_Tbasic = 11,                    /* Tbasic  */
+  YYSYMBOL_Tparen = 12,                    /* Tparen  */
+  YYSYMBOL_Tblock = 13,                    /* Tblock  */
+  YYSYMBOL_Twhile = 14,                    /* Twhile  */
+  YYSYMBOL_15_n_ = 15,                     /* '\n'  */
+  YYSYMBOL_16_ = 16,                       /* '$'  */
+  YYSYMBOL_Tcount = 17,                    /* Tcount  */
+  YYSYMBOL_Tflat = 18,                     /* Tflat  */
+  YYSYMBOL_19_ = 19,                       /* '('  */
+  YYSYMBOL_20_ = 20,                       /* ')'  */
+  YYSYMBOL_21_ = 21,                       /* '{'  */
+  YYSYMBOL_22_ = 22,                       /* '}'  */
+  YYSYMBOL_23_ = 23,                       /* ';'  */
+  YYSYMBOL_24_ = 24,                       /* '&'  */
+  YYSYMBOL_25_ = 25,                       /* '='  */
+  YYSYMBOL_26_ = 26,                       /* '^'  */
+  YYSYMBOL_YYACCEPT = 27,                  /* $accept  */
+  YYSYMBOL_rc = 28,                        /* rc  */
+  YYSYMBOL_line = 29,                      /* line  */
+  YYSYMBOL_body = 30,                      /* body  */
+  YYSYMBOL_paren = 31,                     /* paren  */
+  YYSYMBOL_block = 32,                     /* block  */
+  YYSYMBOL_cmds = 33,                      /* cmds  */
+  YYSYMBOL_cmdsln = 34,                    /* cmdsln  */
+  YYSYMBOL_ifbody = 35,                    /* ifbody  */
+  YYSYMBOL_assign = 36,                    /* assign  */
+  YYSYMBOL_cmd = 37,                       /* cmd  */
+  YYSYMBOL_basic = 38,                     /* basic  */
+  YYSYMBOL_atom = 39,                      /* atom  */
+  YYSYMBOL_word = 40,                      /* word  */
+  YYSYMBOL_executable = 41,                /* executable  */
+  YYSYMBOL_nonkeyword = 42,                /* nonkeyword  */
+  YYSYMBOL_keyword = 43,                   /* keyword  */
+  YYSYMBOL_wordsnl = 44,                   /* wordsnl  */
+  YYSYMBOL_nl = 45                         /* nl  */
 };
 typedef enum yysymbol_kind_t yysymbol_kind_t;
 
@@ -472,21 +473,21 @@ union yyalloc
 #endif /* !YYCOPY_NEEDED */
 
 /* YYFINAL -- State number of the termination state.  */
-#define YYFINAL  31
+#define YYFINAL  37
 /* YYLAST -- Last index in YYTABLE.  */
-#define YYLAST   91
+#define YYLAST   97
 
 /* YYNTOKENS -- Number of terminals.  */
-#define YYNTOKENS  26
+#define YYNTOKENS  27
 /* YYNNTS -- Number of nonterminals.  */
 #define YYNNTS  19
 /* YYNRULES -- Number of rules.  */
-#define YYNRULES  41
+#define YYNRULES  45
 /* YYNSTATES -- Number of states.  */
-#define YYNSTATES  61
+#define YYNSTATES  67
 
 /* YYMAXUTOK -- Last valid token kind.  */
-#define YYMAXUTOK   270
+#define YYMAXUTOK   271
 
 
 /* YYTRANSLATE(TOKEN-NUM) -- Symbol number corresponding to TOKEN-NUM
@@ -501,18 +502,18 @@ union yyalloc
 static const yytype_int8 yytranslate[] =
 {
        0,     2,     2,     2,     2,     2,     2,     2,     2,     2,
-      14,     2,     2,     2,     2,     2,     2,     2,     2,     2,
+      15,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
-       2,     2,     2,     2,     2,     2,    15,     2,    23,     2,
-      18,    19,     2,     2,     2,     2,     2,     2,     2,     2,
-       2,     2,     2,     2,     2,     2,     2,     2,     2,    22,
-       2,    24,     2,     2,     2,     2,     2,     2,     2,     2,
+       2,     2,     2,     2,     2,     2,    16,     2,    24,     2,
+      19,    20,     2,     2,     2,     2,     2,     2,     2,     2,
+       2,     2,     2,     2,     2,     2,     2,     2,     2,    23,
+       2,    25,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
-       2,     2,     2,     2,    25,     2,     2,     2,     2,     2,
+       2,     2,     2,     2,    26,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
-       2,     2,     2,    20,     2,    21,     2,     2,     2,     2,
+       2,     2,     2,    21,     2,    22,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
@@ -526,8 +527,8 @@ static const yytype_int8 yytranslate[] =
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     1,     2,     3,     4,
-       5,     6,     7,     8,     9,    10,    11,    12,    13,    16,
-      17
+       5,     6,     7,     8,     9,    10,    11,    12,    13,    14,
+      17,    18
 };
 
 #if YYDEBUG
@@ -536,9 +537,9 @@ static const yytype_int8 yyrline[] =
 {
        0,    36,    36,    37,    40,    41,    44,    45,    48,    51,
       54,    55,    58,    59,    62,    63,    66,    69,    70,    71,
-      72,    73,    76,    77,    86,    87,    90,    91,    94,    95,
-      98,    99,   100,   101,   102,   106,   106,   113,   114,   115,
-     117,   119
+      72,    73,    74,    75,    78,    79,    88,    89,    92,    93,
+      96,    97,   100,   101,   102,   103,   104,   108,   108,   108,
+     108,   115,   116,   117,   119,   121
 };
 #endif
 
@@ -555,11 +556,12 @@ static const char *yysymbol_name (yysymbol_kind_t yysymbol) YY_ATTRIBUTE_UNUSED;
 static const char *const yytname[] =
 {
   "\"end of file\"", "error", "\"invalid token\"", "Tword", "Twords",
-  "Tif", "Telse", "Tbang", "Targs", "Tindex", "Tbasic", "Tparen", "Tblock",
-  "Twhile", "'\\n'", "'$'", "Tcount", "Tflat", "'('", "')'", "'{'", "'}'",
-  "';'", "'&'", "'='", "'^'", "$accept", "rc", "line", "body", "paren",
-  "block", "cmds", "cmdsln", "ifbody", "assign", "cmd", "basic", "atom",
-  "word", "executable", "nonkeyword", "keyword", "wordsnl", "nl", YY_NULLPTR
+  "Tif", "Telse", "Tbang", "Tsubshell", "Targs", "Tindex", "Tbasic",
+  "Tparen", "Tblock", "Twhile", "'\\n'", "'$'", "Tcount", "Tflat", "'('",
+  "')'", "'{'", "'}'", "';'", "'&'", "'='", "'^'", "$accept", "rc", "line",
+  "body", "paren", "block", "cmds", "cmdsln", "ifbody", "assign", "cmd",
+  "basic", "atom", "word", "executable", "nonkeyword", "keyword",
+  "wordsnl", "nl", YY_NULLPTR
 };
 
 static const char *
@@ -569,7 +571,7 @@ yysymbol_name (yysymbol_kind_t yysymbol)
 }
 #endif
 
-#define YYPACT_NINF (-22)
+#define YYPACT_NINF (-19)
 
 #define yypact_value_is_default(Yyn) \
   ((Yyn) == YYPACT_NINF)
@@ -583,13 +585,13 @@ yysymbol_name (yysymbol_kind_t yysymbol)
    STATE-NUM.  */
 static const yytype_int8 yypact[] =
 {
-      14,   -22,   -17,    73,    73,    73,   -22,    52,    10,     2,
-     -22,    52,    52,     1,    73,    16,   -22,    52,   -22,   -22,
-     -22,   -22,   -22,   -22,   -22,   -22,    68,     7,   -22,    52,
-      13,   -22,   -22,   -22,   -22,   -22,   -22,   -22,    -5,    73,
-      73,    18,    46,   -22,   -22,    -5,   -22,   -22,   -22,    73,
-      -5,   -22,   -22,   -22,    27,   -22,   -22,   -22,   -22,    46,
-     -22
+      18,   -19,   -18,    24,    24,    78,    78,    78,   -19,    24,
+       5,     7,   -19,    24,    24,    -4,    78,    41,   -19,    24,
+     -19,   -19,   -19,   -19,   -19,   -19,   -19,   -19,   -19,   -19,
+     -19,   -19,    72,    -6,   -19,    24,    29,   -19,   -19,   -19,
+     -19,   -19,   -19,   -19,    -2,    78,    78,    10,    55,   -19,
+     -19,    -2,   -19,   -19,   -19,    78,    -2,   -19,   -19,   -19,
+      43,   -19,   -19,   -19,   -19,    55,   -19
 };
 
 /* YYDEFACT[STATE-NUM] -- Default reduction number in state STATE-NUM.
@@ -597,27 +599,27 @@ static const yytype_int8 yypact[] =
    means the default is an error.  */
 static const yytype_int8 yydefact[] =
 {
-      17,    30,     0,     0,     0,     0,    37,    17,     0,     0,
-      19,    17,    17,     4,    18,    22,    28,    17,    40,    35,
-      36,    31,    24,    25,    33,    34,     0,     0,    12,    17,
-       6,     1,     3,     5,    20,    10,    11,    26,    23,     0,
-       0,     0,    17,    38,    32,    39,     9,     7,    13,     0,
-      16,    29,     8,    41,    19,    21,    14,    27,    40,    17,
-      15
+      17,    32,     0,    17,    17,     0,     0,     0,    41,    17,
+       0,     0,    19,    17,    17,     4,    18,    24,    30,    17,
+      44,    22,    23,    37,    38,    39,    40,    33,    26,    27,
+      35,    36,     0,     0,    12,    17,     6,     1,     3,     5,
+      20,    10,    11,    28,    25,     0,     0,     0,    17,    42,
+      34,    43,     9,     7,    13,     0,    16,    31,     8,    45,
+      19,    21,    14,    29,    44,    17,    15
 };
 
 /* YYPGOTO[NTERM-NUM].  */
 static const yytype_int8 yypgoto[] =
 {
-     -22,   -22,    11,    -8,   -22,     4,    15,   -22,   -22,   -22,
-       0,   -22,     3,   -21,   -22,    -1,   -22,   -22,   -14
+     -19,   -19,    42,    -7,   -19,     9,     2,   -19,   -19,   -19,
+       0,   -19,     4,     6,   -19,     1,   -19,   -19,   -10
 };
 
 /* YYDEFGOTO[NTERM-NUM].  */
 static const yytype_int8 yydefgoto[] =
 {
-       0,     8,     9,    27,    18,    10,    28,    29,    55,    12,
-      30,    14,    37,    38,    15,    16,    23,    26,    42
+       0,    10,    11,    33,    20,    12,    34,    35,    61,    14,
+      36,    16,    43,    44,    17,    18,    29,    32,    48
 };
 
 /* YYTABLE[YYPACT[STATE-NUM]] -- What to do in state STATE-NUM.  If
@@ -625,53 +627,53 @@ static const yytype_int8 yydefgoto[] =
    number is the opposite.  If YYTABLE_NINF, syntax error.  */
 static const yytype_int8 yytable[] =
 {
-      13,    17,    22,    22,    22,    45,    21,    24,    25,    41,
-      31,    13,    34,    22,    -2,    11,    32,     1,    50,     2,
-      49,    47,    33,    35,    36,    22,    11,    48,    46,     3,
-       4,     5,     6,    58,     7,    35,    36,    52,    22,    22,
-      39,    40,    56,    51,    59,     0,    54,     0,    22,     1,
-       0,     2,    57,     0,     0,     1,     0,     2,     0,    60,
-      53,     3,     4,     5,     6,     0,     7,     3,     4,     5,
-       6,     1,     7,    19,    20,     0,     1,     0,    19,    20,
-       0,     0,    43,     3,     4,     5,     6,    44,     3,     4,
-       5,     6
+      15,    19,    13,    21,    22,    37,    28,    28,    28,    27,
+      30,    31,    47,    15,    40,    13,    52,    28,    -2,    41,
+      42,     1,    38,     2,    55,     3,     4,     1,    53,     2,
+      58,     3,     4,    28,     5,     6,     7,     8,    51,     9,
+       5,     6,     7,     8,    54,     9,    28,    28,    62,    64,
+      57,    56,    41,    42,    65,    39,    28,    60,     1,    63,
+       2,     0,     3,     4,     0,    66,    45,    46,     0,     0,
+      59,     5,     6,     7,     8,     1,     9,    23,    24,    25,
+      26,     1,     0,    23,    24,    25,    26,    49,     5,     6,
+       7,     8,    50,     0,     5,     6,     7,     8
 };
 
 static const yytype_int8 yycheck[] =
 {
-       0,    18,     3,     4,     5,    26,     3,     4,     5,    17,
-       0,    11,    12,    14,     0,     0,    14,     3,    39,     5,
-      25,    29,    11,    22,    23,    26,    11,    14,    21,    15,
-      16,    17,    18,     6,    20,    22,    23,    19,    39,    40,
-      24,    25,    42,    40,    58,    -1,    42,    -1,    49,     3,
-      -1,     5,    49,    -1,    -1,     3,    -1,     5,    -1,    59,
-      14,    15,    16,    17,    18,    -1,    20,    15,    16,    17,
-      18,     3,    20,     5,     6,    -1,     3,    -1,     5,     6,
-      -1,    -1,    14,    15,    16,    17,    18,    19,    15,    16,
-      17,    18
+       0,    19,     0,     3,     4,     0,     5,     6,     7,     5,
+       6,     7,    19,    13,    14,    13,    22,    16,     0,    23,
+      24,     3,    15,     5,    26,     7,     8,     3,    35,     5,
+      20,     7,     8,    32,    16,    17,    18,    19,    32,    21,
+      16,    17,    18,    19,    15,    21,    45,    46,    48,     6,
+      46,    45,    23,    24,    64,    13,    55,    48,     3,    55,
+       5,    -1,     7,     8,    -1,    65,    25,    26,    -1,    -1,
+      15,    16,    17,    18,    19,     3,    21,     5,     6,     7,
+       8,     3,    -1,     5,     6,     7,     8,    15,    16,    17,
+      18,    19,    20,    -1,    16,    17,    18,    19
 };
 
 /* YYSTOS[STATE-NUM] -- The symbol kind of the accessing symbol of
    state STATE-NUM.  */
 static const yytype_int8 yystos[] =
 {
-       0,     3,     5,    15,    16,    17,    18,    20,    27,    28,
-      31,    32,    35,    36,    37,    40,    41,    18,    30,     5,
-       6,    38,    41,    42,    38,    38,    43,    29,    32,    33,
-      36,     0,    14,    28,    36,    22,    23,    38,    39,    24,
-      25,    29,    44,    14,    19,    39,    21,    29,    14,    25,
-      39,    38,    19,    14,    31,    34,    36,    38,     6,    44,
-      36
+       0,     3,     5,     7,     8,    16,    17,    18,    19,    21,
+      28,    29,    32,    33,    36,    37,    38,    41,    42,    19,
+      31,    37,    37,     5,     6,     7,     8,    39,    42,    43,
+      39,    39,    44,    30,    33,    34,    37,     0,    15,    29,
+      37,    23,    24,    39,    40,    25,    26,    30,    45,    15,
+      20,    40,    22,    30,    15,    26,    40,    39,    20,    15,
+      32,    35,    37,    39,     6,    45,    37
 };
 
 /* YYR1[RULE-NUM] -- Symbol kind of the left-hand side of rule RULE-NUM.  */
 static const yytype_int8 yyr1[] =
 {
-       0,    26,    27,    27,    28,    28,    29,    29,    30,    31,
-      32,    32,    33,    33,    34,    34,    35,    36,    36,    36,
-      36,    36,    37,    37,    38,    38,    39,    39,    40,    40,
-      41,    41,    41,    41,    41,    42,    42,    43,    43,    43,
-      44,    44
+       0,    27,    28,    28,    29,    29,    30,    30,    31,    32,
+      33,    33,    34,    34,    35,    35,    36,    37,    37,    37,
+      37,    37,    37,    37,    38,    38,    39,    39,    40,    40,
+      41,    41,    42,    42,    42,    42,    42,    43,    43,    43,
+      43,    44,    44,    44,    45,    45
 };
 
 /* YYR2[RULE-NUM] -- Number of symbols on the right-hand side of rule RULE-NUM.  */
@@ -679,9 +681,9 @@ static const yytype_int8 yyr2[] =
 {
        0,     2,     0,     2,     1,     2,     1,     2,     3,     3,
        2,     2,     1,     2,     1,     4,     3,     0,     1,     1,
-       2,     4,     1,     2,     1,     1,     1,     3,     1,     3,
-       1,     2,     3,     2,     2,     1,     1,     0,     2,     2,
-       0,     2
+       2,     4,     2,     2,     1,     2,     1,     1,     1,     3,
+       1,     3,     1,     2,     3,     2,     2,     1,     1,     1,
+       1,     0,     2,     2,     0,     2
 };
 
 
@@ -1417,149 +1419,161 @@ yyreduce:
   case 2: /* rc: %empty  */
 #line 36 "sys/cmd/rc/syntax.y"
             { return 0; }
-#line 1421 "sys/cmd/rc/parse.c"
+#line 1423 "sys/cmd/rc/parse.c"
     break;
 
   case 3: /* rc: line '\n'  */
 #line 37 "sys/cmd/rc/syntax.y"
             { return compile((yyvsp[-1].tree)); }
-#line 1427 "sys/cmd/rc/parse.c"
+#line 1429 "sys/cmd/rc/parse.c"
     break;
 
   case 5: /* line: cmds line  */
 #line 41 "sys/cmd/rc/syntax.y"
             { (yyval.tree) = maketree2(';', (yyvsp[-1].tree), (yyvsp[0].tree)); }
-#line 1433 "sys/cmd/rc/parse.c"
+#line 1435 "sys/cmd/rc/parse.c"
     break;
 
   case 7: /* body: cmdsln body  */
 #line 45 "sys/cmd/rc/syntax.y"
               { (yyval.tree) = maketree2(';', (yyvsp[-1].tree), (yyvsp[0].tree)); }
-#line 1439 "sys/cmd/rc/parse.c"
+#line 1441 "sys/cmd/rc/parse.c"
     break;
 
   case 8: /* paren: '(' body ')'  */
 #line 48 "sys/cmd/rc/syntax.y"
                { (yyval.tree) = maketree1(Tparen, (yyvsp[-1].tree)); }
-#line 1445 "sys/cmd/rc/parse.c"
+#line 1447 "sys/cmd/rc/parse.c"
     break;
 
   case 9: /* block: '{' body '}'  */
 #line 51 "sys/cmd/rc/syntax.y"
                { (yyval.tree) = maketree1(Tblock, (yyvsp[-1].tree)); }
-#line 1451 "sys/cmd/rc/parse.c"
+#line 1453 "sys/cmd/rc/parse.c"
     break;
 
   case 11: /* cmds: cmd '&'  */
 #line 55 "sys/cmd/rc/syntax.y"
           { (yyval.tree) = maketree1('&', (yyvsp[-1].tree)); }
-#line 1457 "sys/cmd/rc/parse.c"
+#line 1459 "sys/cmd/rc/parse.c"
     break;
 
   case 14: /* ifbody: cmd  */
 #line 62 "sys/cmd/rc/syntax.y"
                      { (yyval.tree) = maketree2(Tif, nil, (yyvsp[0].tree)); }
-#line 1463 "sys/cmd/rc/parse.c"
+#line 1465 "sys/cmd/rc/parse.c"
     break;
 
   case 15: /* ifbody: block Telse nl cmd  */
 #line 63 "sys/cmd/rc/syntax.y"
                      { (yyval.tree) = maketree3(Tif, nil, (yyvsp[-3].tree), (yyvsp[-2].tree)); }
-#line 1469 "sys/cmd/rc/parse.c"
+#line 1471 "sys/cmd/rc/parse.c"
     break;
 
   case 16: /* assign: executable '=' word  */
 #line 66 "sys/cmd/rc/syntax.y"
                         { (yyval.tree) = maketree2('=', (yyvsp[-2].tree), (yyvsp[0].tree)); }
-#line 1475 "sys/cmd/rc/parse.c"
+#line 1477 "sys/cmd/rc/parse.c"
     break;
 
   case 17: /* cmd: %empty  */
 #line 69 "sys/cmd/rc/syntax.y"
                           { (yyval.tree) = nil; }
-#line 1481 "sys/cmd/rc/parse.c"
+#line 1483 "sys/cmd/rc/parse.c"
     break;
 
   case 18: /* cmd: basic  */
 #line 70 "sys/cmd/rc/syntax.y"
                           { (yyval.tree) = maketree1(Tbasic, (yyvsp[0].tree)); }
-#line 1487 "sys/cmd/rc/parse.c"
+#line 1489 "sys/cmd/rc/parse.c"
     break;
 
   case 20: /* cmd: assign cmd  */
 #line 72 "sys/cmd/rc/syntax.y"
                           { (yyval.tree) = hangchild1((yyvsp[-1].tree), (yyvsp[0].tree), 2); }
-#line 1493 "sys/cmd/rc/parse.c"
+#line 1495 "sys/cmd/rc/parse.c"
     break;
 
   case 21: /* cmd: Tif paren nl ifbody  */
 #line 73 "sys/cmd/rc/syntax.y"
                           { (yyval.tree) = hangchild1((yyvsp[-2].tree), (yyvsp[-3].tree), 0); }
-#line 1499 "sys/cmd/rc/parse.c"
+#line 1501 "sys/cmd/rc/parse.c"
+    break;
+
+  case 22: /* cmd: Tbang cmd  */
+#line 74 "sys/cmd/rc/syntax.y"
+                          { (yyval.tree) = maketree1(Tbang, (yyvsp[0].tree)); }
+#line 1507 "sys/cmd/rc/parse.c"
+    break;
+
+  case 23: /* cmd: Tsubshell cmd  */
+#line 75 "sys/cmd/rc/syntax.y"
+                          { (yyval.tree) = maketree1(Tsubshell, (yyvsp[0].tree)); }
+#line 1513 "sys/cmd/rc/parse.c"
     break;
 
-  case 23: /* basic: basic word  */
-#line 77 "sys/cmd/rc/syntax.y"
+  case 25: /* basic: basic word  */
+#line 79 "sys/cmd/rc/syntax.y"
                       { (yyval.tree) = maketree2(Targs, (yyvsp[-1].tree), (yyvsp[0].tree)); }
-#line 1505 "sys/cmd/rc/parse.c"
+#line 1519 "sys/cmd/rc/parse.c"
     break;
 
-  case 25: /* atom: keyword  */
-#line 87 "sys/cmd/rc/syntax.y"
+  case 27: /* atom: keyword  */
+#line 89 "sys/cmd/rc/syntax.y"
                       { (yyval.tree) = maketree1(Tword, (yyvsp[0].tree)); }
-#line 1511 "sys/cmd/rc/parse.c"
+#line 1525 "sys/cmd/rc/parse.c"
     break;
 
-  case 27: /* word: word '^' atom  */
-#line 91 "sys/cmd/rc/syntax.y"
+  case 29: /* word: word '^' atom  */
+#line 93 "sys/cmd/rc/syntax.y"
                       { (yyval.tree) = maketree2('^', (yyvsp[-2].tree), (yyvsp[0].tree)); }
-#line 1517 "sys/cmd/rc/parse.c"
+#line 1531 "sys/cmd/rc/parse.c"
     break;
 
-  case 29: /* executable: executable '^' atom  */
-#line 95 "sys/cmd/rc/syntax.y"
+  case 31: /* executable: executable '^' atom  */
+#line 97 "sys/cmd/rc/syntax.y"
                       { (yyval.tree) = maketree2('^', (yyvsp[-2].tree), (yyvsp[0].tree)); }
-#line 1523 "sys/cmd/rc/parse.c"
+#line 1537 "sys/cmd/rc/parse.c"
     break;
 
-  case 31: /* nonkeyword: '$' atom  */
-#line 99 "sys/cmd/rc/syntax.y"
+  case 33: /* nonkeyword: '$' atom  */
+#line 101 "sys/cmd/rc/syntax.y"
                   { (yyval.tree) = maketree1('$', (yyvsp[0].tree)); }
-#line 1529 "sys/cmd/rc/parse.c"
+#line 1543 "sys/cmd/rc/parse.c"
     break;
 
-  case 32: /* nonkeyword: '(' wordsnl ')'  */
-#line 100 "sys/cmd/rc/syntax.y"
+  case 34: /* nonkeyword: '(' wordsnl ')'  */
+#line 102 "sys/cmd/rc/syntax.y"
                   { (yyval.tree) = (yyvsp[-1].tree); }
-#line 1535 "sys/cmd/rc/parse.c"
+#line 1549 "sys/cmd/rc/parse.c"
     break;
 
-  case 33: /* nonkeyword: Tcount atom  */
-#line 101 "sys/cmd/rc/syntax.y"
+  case 35: /* nonkeyword: Tcount atom  */
+#line 103 "sys/cmd/rc/syntax.y"
                   { (yyval.tree) = maketree1(Tcount, (yyvsp[0].tree)); }
-#line 1541 "sys/cmd/rc/parse.c"
+#line 1555 "sys/cmd/rc/parse.c"
     break;
 
-  case 34: /* nonkeyword: Tflat atom  */
-#line 102 "sys/cmd/rc/syntax.y"
+  case 36: /* nonkeyword: Tflat atom  */
+#line 104 "sys/cmd/rc/syntax.y"
                   { (yyval.tree) = maketree1(Tflat, (yyvsp[0].tree)); }
-#line 1547 "sys/cmd/rc/parse.c"
+#line 1561 "sys/cmd/rc/parse.c"
     break;
 
-  case 37: /* wordsnl: %empty  */
-#line 113 "sys/cmd/rc/syntax.y"
+  case 41: /* wordsnl: %empty  */
+#line 115 "sys/cmd/rc/syntax.y"
                { (yyval.tree) = nil; }
-#line 1553 "sys/cmd/rc/parse.c"
+#line 1567 "sys/cmd/rc/parse.c"
     break;
 
-  case 39: /* wordsnl: wordsnl word  */
-#line 115 "sys/cmd/rc/syntax.y"
+  case 43: /* wordsnl: wordsnl word  */
+#line 117 "sys/cmd/rc/syntax.y"
                {(yyval.tree) = (!(yyvsp[-1].tree)) ? ((!(yyvsp[0].tree)) ? nil : (yyvsp[0].tree)) : ((!(yyvsp[0].tree)) ? (yyvsp[-1].tree) : maketree2(Twords, (yyvsp[-1].tree), (yyvsp[0].tree))); }
-#line 1559 "sys/cmd/rc/parse.c"
+#line 1573 "sys/cmd/rc/parse.c"
     break;
 
 
-#line 1563 "sys/cmd/rc/parse.c"
+#line 1577 "sys/cmd/rc/parse.c"
 
       default: break;
     }
@@ -1783,5 +1797,5 @@ yyreturnlab:
   return yyresult;
 }
 
-#line 120 "sys/cmd/rc/syntax.y"
+#line 122 "sys/cmd/rc/syntax.y"
 
diff --git a/sys/cmd/rc/parse.h b/sys/cmd/rc/parse.h
index 85be043..b42cc2b 100644
--- a/sys/cmd/rc/parse.h
+++ b/sys/cmd/rc/parse.h
@@ -59,14 +59,15 @@ extern int yydebug;
     Tif = 260,                     /* Tif  */
     Telse = 261,                   /* Telse  */
     Tbang = 262,                   /* Tbang  */
-    Targs = 263,                   /* Targs  */
-    Tindex = 264,                  /* Tindex  */
-    Tbasic = 265,                  /* Tbasic  */
-    Tparen = 266,                  /* Tparen  */
-    Tblock = 267,                  /* Tblock  */
-    Twhile = 268,                  /* Twhile  */
-    Tcount = 269,                  /* Tcount  */
-    Tflat = 270                    /* Tflat  */
+    Tsubshell = 263,               /* Tsubshell  */
+    Targs = 264,                   /* Targs  */
+    Tindex = 265,                  /* Tindex  */
+    Tbasic = 266,                  /* Tbasic  */
+    Tparen = 267,                  /* Tparen  */
+    Tblock = 268,                  /* Tblock  */
+    Twhile = 269,                  /* Twhile  */
+    Tcount = 270,                  /* Tcount  */
+    Tflat = 271                    /* Tflat  */
   };
   typedef enum yytokentype yytoken_kind_t;
 #endif
@@ -80,14 +81,15 @@ extern int yydebug;
 #define Tif 260
 #define Telse 261
 #define Tbang 262
-#define Targs 263
-#define Tindex 264
-#define Tbasic 265
-#define Tparen 266
-#define Tblock 267
-#define Twhile 268
-#define Tcount 269
-#define Tflat 270
+#define Tsubshell 263
+#define Targs 264
+#define Tindex 265
+#define Tbasic 266
+#define Tparen 267
+#define Tblock 268
+#define Twhile 269
+#define Tcount 270
+#define Tflat 271
 
 /* Value type.  */
 #if ! defined YYSTYPE && ! defined YYSTYPE_IS_DECLARED
@@ -97,7 +99,7 @@ union YYSTYPE
 
     struct Tree *tree;
 
-#line 101 "sys/cmd/rc/parse.h"
+#line 103 "sys/cmd/rc/parse.h"
 
 };
 typedef union YYSTYPE YYSTYPE;
diff --git a/sys/cmd/rc/rc.h b/sys/cmd/rc/rc.h
index 55a4eb2..606ca7b 100644
--- a/sys/cmd/rc/rc.h
+++ b/sys/cmd/rc/rc.h
@@ -207,8 +207,11 @@ void execute(Word *, Word*);
 
 /* wait.c */
 void addwait(Thread *, int);
+void delwait(Thread *, int);
 void clearwait(Thread*);
+
 int  waitall(Thread *);
+int  waitfor(Thread *, int);
 
 void killzombies(void);
 
diff --git a/sys/cmd/rc/syntax.y b/sys/cmd/rc/syntax.y
index 469260f..6334819 100644
--- a/sys/cmd/rc/syntax.y
+++ b/sys/cmd/rc/syntax.y
@@ -1,4 +1,4 @@
-%token Tword Twords Tif Telse Tbang
+%token Tword Twords Tif Telse Tbang Tsubshell
 %token Targs Tindex
 %token Tbasic Tparen Tblock
 
@@ -14,7 +14,7 @@
 /* operator precendence: lowest first */
 %left  Twhile Telse
 %left  '\n'
-%left  Tbang
+%left  Tbang Tsubshell
 %right '$' Tcount Tflat
 %right Tindex
 
@@ -24,7 +24,7 @@
 }
 %type<tree> line cmds cmdsln body paren block ifbody assign;
 %type<tree> cmd basic executable nonkeyword keyword word words wordsnl atom arg args;
-%type<tree> Tbang;
+%type<tree> Tbang Tsubshell Tindex;
 %type<tree> Tword Tif Telse;
 
 /* grammar */
@@ -71,6 +71,8 @@ cmd:
 | block
 | assign cmd %prec Tbang  { $$ = hangchild1($1, $2, 2); }
 | Tif paren nl ifbody     { $$ = hangchild1($2, $1, 0); }
+| Tbang cmd               { $$ = maketree1(Tbang, $2); }
+| Tsubshell cmd           { $$ = maketree1(Tsubshell, $2); }
 
 basic:
   executable
@@ -103,7 +105,7 @@ nonkeyword:
 //| '`'  block      { $$ = maketree1('`', $2); }
 
 keyword:
-    Tif|Telse
+    Tif|Telse|Tbang|Tsubshell
 
 words:
 /* empty */  { $$ = nil; }
diff --git a/sys/cmd/rc/wait.c b/sys/cmd/rc/wait.c
index e3dcea1..6a8d859 100644
--- a/sys/cmd/rc/wait.c
+++ b/sys/cmd/rc/wait.c
@@ -84,6 +84,39 @@ shouldwait(Thread *job)
     return 0;
 }
 
+static inline
+void
+notify(Thread *job, struct WaitMsg msg)
+{
+    int i;
+    for(i=0; i < job->wait.len; i++){
+        if(job->wait.on[i].pid == msg.pid){
+            job->status = msg.status;
+            switch(msg.type){
+            case Pstop:
+                print(shell.err, "%d: suspended\n", msg.pid);
+                job->wait.status = Pstop;
+                job->wait.on[i].status = Pstop;
+                break;
+
+            case Psig:
+                print(shell.err, "%d: terminated by signal %d\n", msg.pid, msg.status);
+                /* fallthrough */
+            case Pdone:
+                job->wait.on[i].status = Pdone;
+                delwait(job, msg.pid);
+                if(!job->wait.len)
+                    job->wait.status = Pdone;
+                break;
+
+            default:
+                fatal("%d: unrecognized message type %d\n", msg.pid, msg.type);
+            }
+            break;
+        }
+    }
+}
+
 // -----------------------------------------------------------------------
 // exported
 
@@ -140,34 +173,31 @@ waitall(Thread *job)
             return 0;
         }
 
-        for(i=0; i < job->wait.len; i++){
-            if(job->wait.on[i].pid == msg.pid){
-                job->status = msg.status;
-                switch(msg.type){
-                case Pstop:
-                    print(shell.err, "%d: suspended\n", msg.pid);
-                    job->wait.status = Pstop;
-                    job->wait.on[i].status = Pstop;
-                    break;
-
-                case Psig:
-                    print(shell.err, "%d: terminated by signal %d\n", msg.pid, msg.status);
-                    /* fallthrough */
-                case Pdone:
-                    job->wait.on[i].status = Pdone;
-                    delwait(job, msg.pid);
-                    if(!job->wait.len)
-                        job->wait.status = Pdone;
-                    break;
-
-                default:
-                    fatal("%d: unrecognized message type %d\n", msg.pid, msg.type);
-                }
-                break;
-            }
+        notify(job, msg);
+    }
+    return 1;
+}
+
+int
+waitfor(Thread *job, int pid)
+{
+    int i;
+    Thread *t;
+    struct WaitMsg msg;
+
+    while(shouldwait(job) && await(-job->pgid, WUNTRACED, &msg)){
+        if(msg.pid == 0){
+            perror("wait for");
+            return 0;
         }
+
+        notify(job, msg);
+        /* allow for an early exit */
+        if(msg.pid == pid)
+            return 1;
     }
     return 1;
+
 }
 
 void
@@ -197,30 +227,3 @@ killzombies(void)
         }
     }
 }
-
-#if 0
-int
-waitfor(int pid)
-{
-    Thread *t;
-    struct WaitMsg w;
-
-    if(pid >= 0 && !havewait(pid))
-        return 0;
-
-    while(await(-proc->pgid, WUNTRACED, &w)){
-        delwait(w.pid);
-        if(w.pid == pid){
-            if(w.signal)
-                print(errio, "pid[%d]: signal: %d\n", w.pid, w.status);
-            return 1;
-        }
-        for(t=proc->link; t; t=t->link){
-            if(t->pid == w.pid)
-                t->pid = -1;
-        }
-    }
-
-    return 0;
-}
-#endif