evaluating a condition

evaluating a condition

[Gaspar Bakos]

Hi,

As a beginner in zsh, I would have a question concerning an 'if'
structure.

I have the following script, and I would like to print the numbers in the
terminal from ${min} to ${max}, if both of them are smaller than 10.

export min=$3;export max=$4;
        if (($[min]<10 && $[max]<10)) then
	        for i in {${min}..${max}}; do echo $i; done
        fi

However, this prints the numbers even if ${max}>10

Can someone help?

Gaspar

Re: evaluating a condition

[Bart Schaefer]

On Sep 12,  8:41pm, Gaspar Bakos wrote:
} Subject: evaluating a condition
}
} I have the following script, and I would like to print the numbers in the
} terminal from ${min} to ${max}, if both of them are smaller than 10.

At first I thought you'd found a bug in the math parser, but:

} export min=$3;export max=$4;
}         if (($[min]<10 && $[max]<10)) then
                           ^^
There's a metafied space here.  I think zsh is interpreting "\240$[max]" as
an identifier; e.g. if max=11, the identifier name is "\240\061\061".  That
identifier isn't defined, so it's value is 0 which is always < 10.

} 	        for i in {${min}..${max}}; do echo $i; done
}         fi

This is a danger of permitting identifiers to contain non-ascii characters.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Re: evaluating a condition

[Johannes Mähner]

Gaspar Bakos wrote:
> 
> Hi,
> 
> As a beginner in zsh, I would have a question concerning an 'if'
> structure.
> 
> I have the following script, and I would like to print the numbers in the
> terminal from ${min} to ${max}, if both of them are smaller than 10.
> 
> export min=$3;export max=$4;
>         if (($[min]<10 && $[max]<10)) then
>                 for i in {${min}..${max}}; do echo $i; done
>         fi
> 
> However, this prints the numbers even if ${max}>10
> 
> Can someone help?
> 
> Gaspar

What version of zsh are you using?
With zsh 3.1.6, your code works fine

Re: evaluating a condition

[Sweth Chandramouli]

On Sun, Sep 12, 1999 at 11:51:39PM +0000, Bart Schaefer wrote:
> On Sep 12,  8:41pm, Gaspar Bakos wrote:
> } Subject: evaluating a condition
> }
> } I have the following script, and I would like to print the numbers in the
> } terminal from ${min} to ${max}, if both of them are smaller than 10.
> 
> At first I thought you'd found a bug in the math parser, but:
> 
> } export min=$3;export max=$4;
> }         if (($[min]<10 && $[max]<10)) then
>                            ^^
> There's a metafied space here.  I think zsh is interpreting "\240$[max]" as
> an identifier; e.g. if max=11, the identifier name is "\240\061\061".  That
> identifier isn't defined, so it's value is 0 which is always < 10.
	??? what?

	((...)), at least according to the docs (and as implemented in ksh)
is just another syntax for `let '...''.  all the "metafying" (actually, 
quoting is unmetafying) does is prevent the shell from interpreting the 
space as a word separator; once the string to be evaluated is passed to let,
the space is a space again, and let _should_ (and does, in 3.1.6) simply
ignore it, such that the entire block of code does work.

> } 	        for i in {${min}..${max}}; do echo $i; done
> }         fi
> 
> This is a danger of permitting identifiers to contain non-ascii characters.
	??? okay, what did you do to bart?  :)
	i assume you meant non-printable and not non-ascii here, though 
technically a space is still printable.

	one related question that i've long wondered but never about cared 
enough to ask: is there a difference between the $[...] and ${...} notations?

	-- sweth.

-- 
Sweth Chandramouli ; <sweth@gwu.edu>
<a href="http://astaroth.nit.gwu.edu/resume/">Will Work For Food.</a>
<a href="http://astaroth.nit.gwu.edu/~sweth/disc.html">*</a>

Re: evaluating a condition

[Bart Schaefer]

On Sep 13, 12:35pm, Sweth Chandramouli wrote:
> Subject: Re: evaluating a condition
> On Sun, Sep 12, 1999 at 11:51:39PM +0000, Bart Schaefer wrote:
> > On Sep 12,  8:41pm, Gaspar Bakos wrote:
> > } export min=$3;export max=$4;
> > }         if (($[min]<10 && $[max]<10)) then
> >                            ^^
> > There's a metafied space here.  I think zsh is interpreting "\240$[max]" as
> > an identifier; e.g. if max=11, the identifier name is "\240\061\061".  That
> > identifier isn't defined, so it's value is 0 which is always < 10.
> 	??? what?
> 	((...)), at least according to the docs (and as implemented in ksh)
> is just another syntax for `let '...''.  all the "metafying" (actually, 
> quoting is unmetafying) does is prevent the shell from interpreting

I said there was a metafied space there:  I didn't say zsh metafied it.
There's a "\240" character there in the input; cut'n'paste that through
"cat -v" and you'll see "...10 &&M- $[max]...".  This has nothing whatever
to do with zsh's internal "metafication" process.

> > This is a danger of permitting identifiers to contain non-ascii characters.
> 	??? okay, what did you do to bart?  :)
> 	i assume you meant non-printable and not non-ascii here, though 
> technically a space is still printable.

I meant outside the range 0-127 (decimal), though technically I suppose I
actually meant outside the range 27-126.

> 	one related question that i've long wondered but never about cared 
> enough to ask: is there a difference between the $[...] and ${...} notations?

Yeah.  $[...] evaluates ... as a math expression, the same as $((...)).
So really it's completely unnecessary inside ((...)), but I didn't want to
answer too many questions at once.