Re: [Help-bash] Arithmetic evaluation / expansion question

[Andy Chu]

In the statement

echo $(( pd ))

pd is parsed as a variable name, not a "string".  So your question really
reduces to the first thing you mentioned -- undefined variables are coerced
to 0 in arithmetic contexts.

I am working on a bash compatible shell that warns you about this, and
provides the option for it to be a fatal error with 'set -o strict-arith'.
It's not done but it handles this case well, and I appreciate other bug
reports.

http://www.oilshell.org/

bash$ bin/osh
osh$ echo $(( undef ))
Line 1 of '<interactive>'
  echo $(( undef ))
           ^~~~~
osh warning: Coercing undefined value to 0 in arithmetic context
0
osh$ echo $?
0

osh$ set -o strict-arith

osh$ echo $(( undef ))
Line 4 of '<interactive>'
  echo $(( undef ))
           ^~~~~
Coercing undefined value to 0 in arithmetic context
osh$ echo $?
1


On Wed, Oct 10, 2018 at 9:47 AM Bruce Hohl <address@hidden> wrote:

> An arithmetic evaluation / expansion question please:  the man page
> indicates that base 10 is the default, and null or unset variables evaluate
> to zero.
>
> Are strings also evaluated to zero within $(( ))?
> (Except those beginning with 0 which are octals.)
>
> $ pd=abc
> $ echo $pd
> abc
> $ echo $((pd))
> 0
>