nshlib: add expr command support

It is a mini version for the `expr` command, which implements the features of addition, subtraction, multiplication, division and mod.

Reference: https://www.geeksforgeeks.org/expr-command-in-linux-with-examples/

bl2>
bl2> expr 1 + 2
3
bl2> expr
Usage: expr <operand1> <operator> <operand2>
bl2> expr 5 - 2
3
bl2> set hello 10
bl2> expr $hello - 2
8
bl2> expr 8 a 9
Unknown operator
bl2> expr 20 / 5
4
bl2> expr 10 % 4
2
bl2> expr 10 / 0
operand2 invalid
bl2>
bl2> expr mi + 100
invalid parameter
bl2> expr 100 + mi
invalid parameter
bl2> expr 100 + 0
100

Signed-off-by: Junbo Zheng <zhengjunbo1@xiaomi.com>

Author: Junbo-Zheng

nshlib/Kconfig

@@ -359,6 +359,10 @@ config NSH_DISABLE_EXIT
 	bool "Disable exit"
 	default DEFAULT_SMALL && !NSH_TELNET
 
+config NSH_DISABLE_EXPR
+	bool "Disable expr"
+	default DEFAULT_SMALL
+
 config NSH_DISABLE_EXPORT
 	bool "Disable export"
 	default DEFAULT_SMALL

nshlib/nsh_command.c

@@ -26,6 +26,7 @@
 
 #include <string.h>
 #include <assert.h>
+#include <stdlib.h>
 
 #ifdef CONFIG_NSH_BUILTIN_APPS
 #  include <nuttx/lib/builtin.h>
@@ -91,6 +92,10 @@ static int  cmd_false(FAR struct nsh_vtbl_s *vtbl, int argc,
 static int  cmd_exit(FAR struct nsh_vtbl_s *vtbl, int argc, FAR char **argv);
 #endif
 
+#ifndef CONFIG_NSH_DISABLE_EXPR
+static int cmd_expr(FAR struct nsh_vtbl_s *vtbl, int argc, FAR char **argv);
+#endif
+
 static int  cmd_unrecognized(FAR struct nsh_vtbl_s *vtbl, int argc,
                              FAR char **argv);
 
@@ -226,6 +231,11 @@ static const struct cmdmap_s g_cmdmap[] =
   CMD_MAP("exit",     cmd_exit,     1, 1, NULL),
 #endif
 
+#ifndef CONFIG_NSH_DISABLE_EXPR
+  CMD_MAP("expr",     cmd_expr,     4, 4,
+    "<operand1> <operator> <operand2>"),
+#endif
+
 #ifndef CONFIG_NSH_DISABLE_EXPORT
   CMD_MAP("export",   cmd_export,   2, 3, "[<name> [<value>]]"),
 #endif
@@ -1091,6 +1101,74 @@ static int cmd_exit(FAR struct nsh_vtbl_s *vtbl, int argc, FAR char **argv)
 }
 #endif
 
+#ifndef CONFIG_NSH_DISABLE_EXPR
+static int cmd_expr(FAR struct nsh_vtbl_s *vtbl, int argc, FAR char **argv)
+{
+  int operand1;
+  int operand2;
+  int result;
+  FAR char *endptr;
+
+  if (argc != 4)
+    {
+      nsh_output(vtbl, "Usage: %s <operand1> <operator> <operand2>\n",
+                 argv[0]);
+      return ERROR;
+    }
+
+  operand1 = strtol(argv[1], &endptr, 0);
+  if (*endptr != '\0')
+    {
+      nsh_output(vtbl, "operand1 invalid\n");
+      return ERROR;
+    }
+
+  operand2 = strtol(argv[3], &endptr, 0);
+  if (*endptr != '\0')
+    {
+      nsh_output(vtbl, "operand2 invalid\n");
+      return ERROR;
+    }
+
+  switch (argv[2][0])
+    {
+      case '+':
+        result = operand1 + operand2;
+        break;
+      case '-':
+        result = operand1 - operand2;
+        break;
+      case '*':
+        result = operand1 * operand2;
+        break;
+      case '/':
+        if (operand2 == 0)
+          {
+            nsh_output(vtbl, "operand2 invalid\n");
+            return ERROR;
+          }
+
+        result = operand1 / operand2;
+        break;
+      case '%':
+        if (operand2 == 0)
+          {
+            nsh_output(vtbl, "operand2 invalid\n");
+            return ERROR;
+          }
+
+        result = operand1 % operand2;
+        break;
+      default:
+        nsh_output(vtbl, "Unknown operator\n");
+        return ERROR;
+    }
+
+  nsh_output(vtbl, "%d\n", result);
+  return OK;
+}
+#endif
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/