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Re: Inconsistent arithmetic evaluation of parameters
From: |
Greg Wooledge |
Subject: |
Re: Inconsistent arithmetic evaluation of parameters |
Date: |
Wed, 2 Sep 2015 11:48:40 -0400 |
User-agent: |
Mutt/1.4.2.3i |
On Wed, Sep 02, 2015 at 11:24:42AM -0400, Chet Ramey wrote:
> On 9/2/15 11:19 AM, Greg Wooledge wrote:
> > On Wed, Sep 02, 2015 at 10:16:14AM -0500, Dennis Williamson wrote:
> >> The $ is implied.
> >
> > That is completely absurd. (And wrong.)
>
> Not exactly. When the arithmetic evaluator encounters a token that is of
> the form of a shell identifier (`bar'), in a context where an operand is
> needed, it treats it as a shell variable and looks up the variable's
> value. In that sense, it's an expansion.
>
> The difference between bash and dash is what each shell does with that
> value.
$foo and foo are not equivalent in dash, as we've already discussed:
$ dash
$ foo=bar bar=5
$ echo $((foo))
dash: 4: Illegal number: bar
$ echo $(($foo))
5
They are also not equivalent in bash, if I may be permitted to change
the context slightly:
$ bash
$ foo='$(id >&2)'
$ echo $((x[foo]))
bash: $(id >&2): syntax error: operand expected (error token is "$(id >&2)")
$ echo $((x[$foo]))
uid=563(wooledg) gid=22(pgmr) groups=1002(webauth),208(opgmr)
0
So "The $ is implied" is false, in both shells, although there are some
contexts where they happen to produce the same result.
- Re: Inconsistent arithmetic evaluation of parameters, (continued)
- Re: Inconsistent arithmetic evaluation of parameters, Greg Wooledge, 2015/09/01
- Re: Inconsistent arithmetic evaluation of parameters, Dennis Williamson, 2015/09/01
- Re: Inconsistent arithmetic evaluation of parameters, Greg Wooledge, 2015/09/01
- Re: Inconsistent arithmetic evaluation of parameters, Dennis Williamson, 2015/09/01
- Re: Inconsistent arithmetic evaluation of parameters, Andreas Schwab, 2015/09/01
- Re: Inconsistent arithmetic evaluation of parameters, Dennis Williamson, 2015/09/01
- Re: Inconsistent arithmetic evaluation of parameters, Andreas Schwab, 2015/09/02
- Re: Inconsistent arithmetic evaluation of parameters, Dennis Williamson, 2015/09/02
- Re: Inconsistent arithmetic evaluation of parameters, Greg Wooledge, 2015/09/02
- Re: Inconsistent arithmetic evaluation of parameters, Chet Ramey, 2015/09/02
- Re: Inconsistent arithmetic evaluation of parameters,
Greg Wooledge <=
- Re: Inconsistent arithmetic evaluation of parameters, Chet Ramey, 2015/09/03
- Re: Inconsistent arithmetic evaluation of parameters, Chet Ramey, 2015/09/02
- Re: Inconsistent arithmetic evaluation of parameters, Stephane Chazelas, 2015/09/03
- Re: Inconsistent arithmetic evaluation of parameters, Dennis Williamson, 2015/09/03
- Re: Inconsistent arithmetic evaluation of parameters, Chet Ramey, 2015/09/02
- Re: Inconsistent arithmetic evaluation of parameters, Chet Ramey, 2015/09/02