Re: expansion in conditional expression patterns

[Sebastian Stark <seb-zsh@xxxxxxxxxxx>]

On 13.10.2009, at 11:07, Peter Stephenson wrote:

> On Mon, 12 Oct 2009 19:51:14 +0200
> Sebastian Stark <seb-zsh@xxxxxxxxxxx> wrote:
> > % limit=5
> > % if [[ 1 != <2-$limit> ]]; then print outside; fi
> > zsh: parse error: condition expected: 1
> >
> > What part of this do I misunderstand?
>
> Logically this ought to work:  parameter substitution is performed  
> before
> pattern matching or globbing.  However, "<" is rather overloaded and  
> when
> the expression is parsed the shell only decides it's a numeric glob  
> if the
> expression is in the strict form with digits.  It could probably be  
> made
> smarter in this case, where "<" can't be a redirection, but as a  
> knock-on
> effect pattern matching would have to be made smarter about deciding  
> later
> on if the expression was a numeric glob, so it's not entirely trivial.

Thanks for clarifying this.

> Your best bet for now is to do numeric comparisons with -ge and -le  
> or with
> <= and >= in (( ... )) expressions.  You can use an "eval" but  
> that's probably
> a bit too ugly for what you're trying to do.

I just did this:

  if [[ ! ( ($cmdnum -ge 1) && ($cmdnum -le $limit) ) ]]

Maybe I should have asked differently because there might be a better  
solution for what I'm trying to do. I have an array of commands,  
$cmds, and a user supplied $cmdnum. Now I want to check wether the  
user entered a valid number. ($limit would be $#cmds in this example).

Is there a better way to check wether the user entered a) a number and  
b) in the range 1..$#cmds?


Sebastian