hush: more efficient filtering of "safe" arithmetic

function                                             old     new   delta
expand_variables                                    2170    2147     -23

1 files changed, 9 insertions, 19 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 3aae7d7c1..e86f0d22f 100644
--- 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;