Re: [PATCH] fix "Illegal number" on FreeBSD & macOS for x=; echo $((x))

[Martijn Dekker <martijn@xxxxxxxx>]

Op 05-03-18 om 22:41 schreef Harald van Dijk:
> On 3/5/18 1:32 AM, Martijn Dekker wrote:
>> dash compiled on Mac OS X (macOS) and FreeBSD manifests the following
>> bug:
>>
>> $ dash -c 'x=; echo $((x))'
>> dash: 1: Illegal number:
>>
>> This error is printed instead of the expected default "0" that should be
>> substituted for an empty variable in an arithmetic expression.
>>
>> The bug does not occur on Linux, NetBSD, OpenBSD or Solaris.
> 
> There is no reason why dash should behave differently on FreeBSD vs.
> Linux, so I agree with your patch, but isn't this non-standard, isn't
> either behaviour allowed?

I don't think so.

2.6.4 Arithmetic Expansion:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_04
"The arithmetic expression shall be processed according to the rules
given in Arithmetic Precision and Operations [...]".

Arithmetic Precision and Operations:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html#tag_17_01_02_01
"All variables shall be initialized to zero if they are not otherwise
assigned by the input to the application."

Also, consensus among existing shells appears to be universal.

> This looks good, it does the job, but it can be simplified a bit:
> 
> If errno == EINVAL, then p == s is already known.
> 
> If errno != 0 && p == s, then errno == EINVAL is already known.
> 
> This allows simplifying to either of the following:
> 
>   if (errno != 0 && errno != EINVAL)
>   if (errno != 0 && p != s)

Good point.

> But perhaps
> 
>   if (errno == ERANGE)
> 
> is all that's needed here.

Explain?

Thanks,

- M.
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