nsh:support $! get last pid use nsh run

test:
    nsh> hello &
    hello [4:100]
    nsh> Hello, World!!

    nsh> echo $!
    4
    nsh> echo $!
    3
    nsh> ps
      PID GROUP PRI POLICY   TYPE    NPX STATE    EVENT     SIGMASK           STACK COMMAND
        0     0   0 FIFO     Kthread   - Ready              0000000000000000 0069616 Idle_Task
        1     1 224 FIFO     Kthread   - Waiting  Signal    0000000000000000 0067536 loop_task
        2     2 224 FIFO     Kthread   - Waiting  Semaphore 0000000000000000 0067504 hpwork 0x45ae80 0x45aea8
        3     3 100 FIFO     Task      - Running            0000000000000000 0067536 nsh_main
    nsh>

Signed-off-by: anjiahao <anjiahao@xiaomi.com>

nshlib/nsh.h

@@ -659,6 +659,11 @@ struct nsh_parser_s
   bool     np_redir_out; /* true: Output from the last command was re-directed */
   bool     np_redir_in;  /* true: Input from the last command was re-directed */
   bool     np_fail;      /* true: The last command failed */
+  pid_t    np_lastpid;   /* Pid of the last command executed */
+#ifdef NSH_HAVE_VARS
+  char     np_pids[32];  /* String representation of the last pid */
+#endif
+
 #ifndef CONFIG_NSH_DISABLESCRIPT
   uint8_t  np_flags;     /* See nsh_npflags_e above */
 #endif

nshlib/nsh_builtin.c

@@ -121,6 +121,7 @@ int nsh_builtin(FAR struct nsh_vtbl_s *vtbl, FAR const char *cmd,
        *     foreground
        */
 
+       vtbl->np.np_lastpid = ret;
 #ifdef CONFIG_SCHED_WAITPID
 
       /* CONFIG_SCHED_WAITPID is selected, so we may run the command in

nshlib/nsh_command.c

@@ -1256,6 +1256,7 @@ int nsh_command(FAR struct nsh_vtbl_s *vtbl, int argc, FAR char *argv[])
     }
 
   ret = handler(vtbl, argc, argv);
+  vtbl->np.np_lastpid = getpid();
   return ret;
 }
 

nshlib/nsh_fileapps.c

@@ -202,6 +202,7 @@ int nsh_fileapp(FAR struct nsh_vtbl_s *vtbl, FAR const char *cmd,
        *     foreground
        */
 
+       vtbl->np.np_lastpid = pid;
 #ifdef CONFIG_SCHED_WAITPID
       /* CONFIG_SCHED_WAITPID is selected, so we may run the command in
        * foreground unless we were specifically requested to run the command

nshlib/nsh_parse.c

@@ -281,6 +281,7 @@ static const char g_redirect_out2[]  = ">>";
 static const char g_redirect_in1[]   = "<";
 #ifdef NSH_HAVE_VARS
 static const char g_exitstatus[]      = "?";
+static const char g_lastpid[]         = "!";
 static const char g_success[]         = "0";
 static const char g_failure[]         = "1";
 #endif
@@ -1262,6 +1263,11 @@ static FAR char *nsh_envexpand(FAR struct nsh_vtbl_s *vtbl,
           return (FAR char *)g_success;
         }
     }
+  else if (strcmp(varname, g_lastpid) == 0)
+    {
+      itoa(vtbl->np.np_lastpid, vtbl->np.np_pids, 10);
+      return vtbl->np.np_pids;
+    }
   else
     {
       FAR char *value;