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>

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)) {
- 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;
+			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 /* 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

shell/hush_test/hush-vars/var_bash1b.right

@@ -0,0 +1,23 @@
+all    |0123456
+4:     |456
+4:2    |45
+4:-1   |45
+4:-2   |4
+4:-3   |
+-4:    |3456
+-4:2   |34
+-4:-1  |345
+-4:-2  |34
+-4:-3  |3
+-4:-4  |
+-4:i=2 |34
+-4:i=-2|34
+-4:i=-3|3
+-4:i=-4|
+-5:    |23456
+-6:    |123456
+-7:    |0123456
+-8:    |
+-9:    |
+-9:-99 |
+Ok:0

shell/hush_test/hush-vars/var_bash1b.tests

@@ -0,0 +1,24 @@
+set -- 0123456
+	echo "all    |"$1
+	echo "4:     |"${1:4}
+	echo "4:2    |"${1:4:2}
+	echo "4:-1   |"${1:4:-1}
+	echo "4:-2   |"${1:4:-2}
+	echo "4:-3   |"${1:4:-3}
+	echo "-4:    |"${1: -4}
+	echo "-4:2   |"${1: -4:2}
+	echo "-4:-1  |"${1: -4:-1}
+	echo "-4:-2  |"${1: -4:-2}
+	echo "-4:-3  |"${1: -4:-3}
+	echo "-4:-4  |"${1: -4:-4}
+i=2;	echo "-4:i=2 |"${1: -4:i}
+i=-2;	echo "-4:i=-2|"${1: -4:i}
+i=-3;	echo "-4:i=-3|"${1: -4:i}
+i=-4;	echo "-4:i=-4|"${1: -4:i}
+	echo "-5:    |"${1: -5}
+	echo "-6:    |"${1: -6}
+	echo "-7:    |"${1: -7}
+	echo "-8:    |"${1: -8}
+	echo "-9:    |"${1: -9}
+	echo "-9:-99 |"${1: -9:-99}
+echo Ok:$?