hush: more efficient filtering of "safe" arithmetic

function                                             old     new   delta
expand_variables                                    2170    2147     -23

diff --git a/shell/hush.c b/shell/hush.c
index 3aae7d7c11c36b9da62345c92174e745499d7951..e86f0d22f1ee956035640865bf141919950179fe 100644 (file)
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -1782,24 +1782,15 @@ static int expand_vars_to_list(o_string *output, int n, char *arg, char or_mask)
                        debug_printf_subst("ARITH '%s' first_ch %x\n", arg, first_ch);
 
                        /* Optional: skip expansion if expr is simple ("a + 3", "i++" etc) */
-                       exp_str = arg;
-                       while (1) {
-                               unsigned char c = *exp_str++;
-                               if (c == '\0') {
-                                       exp_str = NULL;
-                                       goto skip_expand;
-                               }
-                               if (isdigit(c))
-                                       continue;
-                               if (strchr(" \t+-*/%<>()_", c) != NULL)
-                                       continue;
-                               c |= 0x20; /* tolower */
-                               if (c >= 'a' && c <= 'z')
-                                       continue;
-                               break;
-                       }
-                       /* We need to expand. Example: "echo $(($a + 1)) $((1 + $((2)) ))" */
-                       {
+                       exp_str = NULL;
+                       if (strchr(arg, '$') != NULL
+#if ENABLE_HUSH_TICK
+                        || strchr(arg, '`') != NULL
+#endif
+                       ) {
+                               /* We need to expand. Example:
+                                * echo $(($a + `echo 1`)) $((1 + $((2)) ))
+                                */
                                struct in_str input;
                                o_string dest = NULL_O_STRING;
 
@@ -1810,7 +1801,6 @@ static int expand_vars_to_list(o_string *output, int n, char *arg, char or_mask)
                                //bb_error_msg("'%s' -> '%s'", dest.data, exp_str);
                                o_free(&dest);
                        }
- skip_expand:
                        hooks.lookupvar = get_local_var_value;
                        hooks.setvar = arith_set_local_var;
                        hooks.endofname = endofname;