hush: support ${VAR:N:-M}

function                                             old     new   delta
expand_one_var                                      1602    1615     +13
builtin_type                                         114     116      +2

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

1 files changed, 25 insertions, 23 deletions

diff --git a/shell/hush.c b/shell/hush.c
index fd2a3d0f5..836f3b83c 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -5723,32 +5723,34 @@ static NOINLINE const char *expand_one_var(char **to_be_freed_pp, char *arg, cha
                         if (errmsg)
                                 goto arith_err;
                         debug_printf_varexp("len:'%s'=%lld\n", exp_word, (long long)len);
-                        if (len >= 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)) {
+                        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) {
+                                /* in bash, len=-n means strlen()-n */
+                                len = (arith_t)strlen(val) - beg + len;
+                                if (len < 0) /* bash compat */
+                                        die_if_script("%s: substring expression < 0", var);
+                        }
+                        if (len == 0 || !val || beg >= strlen(val)) {
  arith_err:
-                                        val = NULL;
-                                } else {
-                                        /* Paranoia. What if user entered 9999999999999
-                                         * which fits in arith_t but not int? */
-                                        if (len >= INT_MAX)
-                                                len = INT_MAX;
-                                        val = to_be_freed = xstrndup(val + beg, len);
-                                }
-                                debug_printf_varexp("val:'%s'\n", val);
-                        } else
-//TODO: in bash, len=-n means strlen()-n
-#endif /* HUSH_SUBSTR_EXPANSION && FEATURE_SH_MATH */
-                        {
-                                die_if_script("malformed ${%s:...}", var);
                                 val = NULL;
+                        } else {
+                                /* Paranoia. What if user entered 9999999999999
+                                 * which fits in arith_t but not int? */
+                                if (len >= INT_MAX)
+                                        len = INT_MAX;
+                                val = to_be_freed = xstrndup(val + beg, len);
                         }
+                        debug_printf_varexp("val:'%s'\n", val);
+#else /* not (HUSH_SUBSTR_EXPANSION && FEATURE_SH_MATH) */
+                        die_if_script("malformed ${%s:...}", var);
+                        val = NULL;
+#endif
                 } else { /* one of "-=+?" */
                         /* Standard-mandated substitution ops:
                          * ${var?word} - indicate error if unset