shell: handle $((NUM++...) like bash does. Closes 10706

function                                             old     new   delta
evaluate_string                                      680     729     +49

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/shell/math.c b/shell/math.c
index f01f24362..611b3beab 100644
--- a/shell/math.c
+++ b/shell/math.c
@@ -598,10 +598,24 @@ evaluate_string(arith_state_t *math_state, const char *expr)
                 }
 
                 /* Should be an operator */
+
+                /* Special case: NUM-- and NUM++ are not recognized if NUM
+                 * is a literal number, not a variable. IOW:
+                 * "a+++v" is a++ + v.
+                 * "7+++v" is 7 + ++v, not 7++ + v.
+                 */
+                if (lasttok == TOK_NUM && !numstackptr[-1].var /* number literal */
+                 && (expr[0] == '+' || expr[0] == '-')
+                 && (expr[1] == expr[0])
+                ) {
+                        //bb_error_msg("special %c%c", expr[0], expr[0]);
+                        op = (expr[0] == '+' ? TOK_ADD : TOK_SUB);
+                        expr += 1;
+                        goto tok_found1;
+                }
+
                 p = op_tokens;
                 while (1) {
-// TODO: bash allows 7+++v, treats it as 7 + ++v
-// we treat it as 7++ + v and reject
                         /* Compare expr to current op_tokens[] element */
                         const char *e = expr;
                         while (1) {
@@ -627,6 +641,7 @@ evaluate_string(arith_state_t *math_state, const char *expr)
                 }
  tok_found:
                 op = p[1]; /* fetch TOK_foo value */
+ tok_found1:
                 /* NB: expr now points past the operator */
 
                 /* post grammar: a++ reduce to num */