From f8ddbe1ccce9eceaaac28b4b1aa71631fcc56db6 Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Mon, 25 Jul 2016 03:56:00 +0200
Subject: [PATCH] ash: fix handling of ${VAR: -2}

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
 shell/ash.c                              | 12 ++++++++----
 shell/ash_test/ash-vars/var_bash1a.right |  6 ++++++
 shell/ash_test/ash-vars/var_bash1a.tests | 11 +++++++++++
 3 files changed, 25 insertions(+), 4 deletions(-)
 create mode 100644 shell/ash_test/ash-vars/var_bash1a.right
 create mode 100755 shell/ash_test/ash-vars/var_bash1a.tests

diff --git a/shell/ash.c b/shell/ash.c
index 4f6376f78..496167fbe 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -6323,6 +6323,8 @@ subevalvar(char *p, char *varname, int strloc, int subtype,
 
 #if ENABLE_ASH_BASH_COMPAT
 	case VSSUBSTR:
+//TODO: support more general format ${v:EXPR:EXPR},
+// where EXPR follows $(()) rules
 		loc = str = stackblock() + strloc;
 		/* Read POS in ${var:POS:LEN} */
 		pos = atoi(loc); /* number(loc) errors out on "1:4" */
@@ -11577,15 +11579,18 @@ parsesub: {
 		STPUTC('=', out);
 		flags = 0;
 		if (subtype == 0) {
+			static const char types[] ALIGN1 = "}-+?=";
 			/* ${VAR...} but not $VAR or ${#VAR} */
 			/* c == first char after VAR */
 			switch (c) {
 			case ':':
 				c = pgetc();
 #if ENABLE_ASH_BASH_COMPAT
-				if (c == ':' || c == '$' || isdigit(c)) {
-//TODO: support more general format ${v:EXPR:EXPR},
-// where EXPR follows $(()) rules
+				/* This check is only needed to not misinterpret
+				 * ${VAR:-WORD}, ${VAR:+WORD}, ${VAR:=WORD}, ${VAR:?WORD}
+				 * constructs.
+				 */
+				if (!strchr(types, c)) {
 					subtype = VSSUBSTR;
 					pungetc();
 					break; /* "goto do_pungetc" is bigger (!) */
@@ -11594,7 +11599,6 @@ parsesub: {
 				flags = VSNUL;
 				/*FALLTHROUGH*/
 			default: {
-				static const char types[] ALIGN1 = "}-+?=";
 				const char *p = strchr(types, c);
 				if (p == NULL)
 					goto badsub;
diff --git a/shell/ash_test/ash-vars/var_bash1a.right b/shell/ash_test/ash-vars/var_bash1a.right
new file mode 100644
index 000000000..1965b5c6c
--- /dev/null
+++ b/shell/ash_test/ash-vars/var_bash1a.right
@@ -0,0 +1,6 @@
+parameter     'abcdef'
+varoffset2    'cdef'
+varoffset-2   'ef'
+literal '2'   'cdef'
+literal '-2'  'abcdef'
+literal ' -2' 'ef'
diff --git a/shell/ash_test/ash-vars/var_bash1a.tests b/shell/ash_test/ash-vars/var_bash1a.tests
new file mode 100755
index 000000000..551dd9acc
--- /dev/null
+++ b/shell/ash_test/ash-vars/var_bash1a.tests
@@ -0,0 +1,11 @@
+parameter=abcdef
+offset=2
+noffset=-2
+echo "parameter     '${parameter}'"
+echo "varoffset2    '${parameter:${offset}}'"
+echo "varoffset-2   '${parameter:${noffset}}'"
+echo "literal '2'   '${parameter:2}'"
+# This is not inrpreted as ${VAR:POS{:LEN}},
+# but as ${VAR:=WORD} - if VAR is unset or null, substitute WORD
+echo "literal '-2'  '${parameter:-2}'"
+echo "literal ' -2' '${parameter: -2}'"