Re: expansion in conditional expression patterns

[Peter Stephenson <pws@xxxxxxx>]

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.

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.

-- 
Peter Stephenson <pws@xxxxxxx>            Software Engineer
Tel: +44 (0)1223 692070                   Cambridge Silicon Radio Limited
Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, UK


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