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Date: Wed, 15 Apr 2015 10:03:24 +0100
From: Peter Stephenson <p.stephenson@samsung.com>
To: zsh-workers@zsh.org
Subject: Re: broken parsing with $((`:`))
Message-id: <20150415100324.296ffa3e@pwslap01u.europe.root.pri>
In-reply-to: <20150415030531.GA8187@vapier>
References: <20150415030531.GA8187@vapier>
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On Tue, 14 Apr 2015 23:05:31 -0400
Mike Frysinger <vapier@gentoo.org> wrote:
> looks like zsh doesn't correctly parse this:
> $ zsh -c 'echo $((`:`))'
> zsh:1: bad math expression: illegal character: \M-]
>
> looks like it's related to the subshell not outputting anything.

Yes, indeed --- there's a funny internal special case for empty strings
that I never quite get my head around.

(Please, God, make the problems with command and math substitution
parsing stop now.)

pws

diff --git a/Src/math.c b/Src/math.c
index c047725..f2c72d5 100644
--- a/Src/math.c
+++ b/Src/math.c
@@ -1398,7 +1398,7 @@ matheval(char *s)
     if (!mlevel)
 	outputradix = outputunderscore = 0;
 
-    if (!*s) {
+    if (!*s || *s == Nularg) {
 	x.type = MN_INTEGER;
 	x.u.l = 0;
 	return x;
diff --git a/Test/C01arith.ztst b/Test/C01arith.ztst
index d3176dd..e2dfe56 100644
--- a/Test/C01arith.ztst
+++ b/Test/C01arith.ztst
@@ -383,4 +383,7 @@
   print ${$(( $1 * 100 ))%%.[0-9]#})
 0:Arithmetic substitution nested in parameter substitution
 >3246
- 
+
+  print $((`:`))
+0:Null string in arithmetic evaluation after command substitution
+>0