sh: arith: Disallow decimal constants starting with 0 (containing 8 o…

…r 9).

Constants in arithmetic starting with 0 should be octal only.

This avoids the following highly puzzling result:
  $ echo $((018-017))
  3
by making it an error instead.

bin/sh/arith_lex.l

@@ -74,12 +74,12 @@ int yylex(void);
 			return ARITH_NUM;
 		}
 
-0[0-7]+		{
+0[0-7]*		{
 			yylval.l_value = strtoarith_t(yytext, NULL, 8);
 			return ARITH_NUM;
 		}
 
-[0-9]+		{
+[1-9][0-9]*	{
 			yylval.l_value = strtoarith_t(yytext, NULL, 10);
 			return ARITH_NUM;
 		}

tools/regression/bin/sh/expansion/arith8.0

@@ -0,0 +1,4 @@
+# $FreeBSD$
+
+v=$( (eval ': $((08))') 2>&1 >/dev/null)
+[ $? -ne 0 ] && [ -n "$v" ]