On 3/19/12 9:27 AM, Mark Edgar wrote:
> I've boiled the problem down to this:
> 
>  A=
>  B=q
>  echo "x${A+${B#q*}}x" | sed -nel
> 
> Excluding the newline, the output I expect is "xx", but instead there
> is a delete character \177 between the two "x" characters.

Thanks for the wonderfully detailed bug report; that made the problem
easy to find and test.  I've attached a patch which fixes the issue.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    c...@case.edu    http://cnswww.cns.cwru.edu/~chet/
*** ../bash-4.2-patched/subst.c	2012-03-11 17:35:13.000000000 -0400
--- subst.c	2012-03-20 19:30:13.000000000 -0400
***************
*** 5805,5808 ****
--- 5814,5827 ----
        if (qdollaratp && ((hasdol && quoted) || l->next))
  	*qdollaratp = 1;
+       /* If we have a quoted null result (QUOTED_NULL(temp)) and the word is
+ 	 a quoted null (l->next == 0 && QUOTED_NULL(l->word->word)), the
+ 	 flags indicate it (l->word->flags & W_HASQUOTEDNULL), and the
+ 	 expansion is quoted (quoted & (Q_HERE_DOCUMENT|Q_DOUBLE_QUOTES))
+ 	 (which is more paranoia than anything else), we need to return the
+ 	 quoted null string and set the flags to indicate it. */
+       if (l->next == 0 && (quoted & (Q_HERE_DOCUMENT|Q_DOUBLE_QUOTES)) && QUOTED_NULL(temp) && QUOTED_NULL(l->word->word) && (l->word->flags & W_HASQUOTEDNULL))
+ 	{
+ 	  w->flags |= W_HASQUOTEDNULL;
+ 	}
        dispose_words (l);
      }

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