hush: implement negative start in the ${v: -n[:m]} idiom
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush.c b/shell/hush.c
index 64b33cf..f6b50de 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -5619,8 +5619,12 @@
goto arith_err;
debug_printf_varexp("len:'%s'=%lld\n", exp_word, (long long)len);
if (len >= 0) { /* bash compat: len < 0 is illegal */
- if (beg < 0) /* bash compat */
- beg = 0;
+ if (beg < 0) {
+ /* negative beg counts from the end */
+ beg = (arith_t)strlen(val) + beg;
+ if (beg < 0) /* ${v: -999999} is "" */
+ beg = len = 0;
+ }
debug_printf_varexp("from val:'%s'\n", val);
if (len == 0 || !val || beg >= strlen(val)) {
arith_err: