On 8/1/11 8:47 PM, Chet Ramey wrote:
> On 8/1/11 4:41 AM, [email protected] wrote:
>> Hello
>>
>> I wanted to check a variable before attempting to divide something by it, so
>> I wrote :
>>
>> echo $(( foo==0?0:something/foo ))
>>
>> And bash 2, 3 and up to 4.2.10 version sent me a "division by 0" error.
>>
>> So, I've tested a static version of the statement :
>>
>> $ echo $(( 0==0?0:1/0 ))
>> -bash: 0==0?0:1/0 : division by 0 (error token is " ")
>>
>> It looks like the "division by 0" happens whatever the condition result.
>> Shouldn't it happen only if condition result make the computing go that far
>> (like, FWIW, in zsh) ?
>
> Hmm...this looks like a precedence problem. I'll take a look.
It's not actually a precedence problem. The check for division by 0
shouldn't take place when evaluation is suppressed. (The bash
arithmetic evaluator, like most others of its type, is parse-and-
evaluate-on-the-fly, so all operands are evaluated.
Please try the attached patch and see if it works for you.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU [email protected] http://cnswww.cns.cwru.edu/~chet/
*** ../bash-4.2-patched/expr.c 2010-12-21 11:12:13.000000000 -0500
--- expr.c 2011-08-02 20:58:28.000000000 -0400
***************
*** 477,480 ****
--- 481,492 ----
if (special)
{
+ if ((op == DIV || op == MOD) && value == 0)
+ {
+ if (noeval == 0)
+ evalerror (_("division by 0"));
+ else
+ value = 1;
+ }
+
switch (op)
{
***************
*** 483,493 ****
break;
case DIV:
- if (value == 0)
- evalerror (_("division by 0"));
lvalue /= value;
break;
case MOD:
- if (value == 0)
- evalerror (_("division by 0"));
lvalue %= value;
break;
--- 495,501 ----
***************
*** 805,809 ****
if (((op == DIV) || (op == MOD)) && (val2 == 0))
! evalerror (_("division by 0"));
if (op == MUL)
--- 813,822 ----
if (((op == DIV) || (op == MOD)) && (val2 == 0))
! {
! if (noeval == 0)
! evalerror (_("division by 0"));
! else
! val2 = 1;
! }
if (op == MUL)
