[GRASS-user] d.polar strange behavior when using MASK

[Stefano Costa]

Il giorno lun, 08/10/2007 alle 17.59 +0100, Glynn Clements ha scritto:
> I must be going blind; I missed that '*' the first time around. '^*$'
> isn't (AFAICT) a valid regexp, as the '*' must be preceded by an
> expression, and I don't think that '^' counts in this context.

I noticed that, but see below for some more details.

> I suspect that this is causing grep to get stuck in an infinite loop. 
> The * operator repeatedly matches the preceding expression until it
> fails. But matching against ^ doesn't advance the pointer, so no
> matter how many times it matches ^, it's still at the start of the
> line.
> 
> If it's meant to eliminate lines which consist of nothing but an
> asterisk, it should be:
> 
>         grep -v '^\*$'

I tried this and it was slow just as its `wrong' counterpart '^*$'.
In fact, I tried both the right and wrong regexps _without_ the -v flag
to see which lines where matching: in both cases ('^*$' and '^\*$')  on
my system all NULL cells (represented by *) were matching the regexp,
and the grep was taking hours to complete. My MASK actually leaves about
99% of the cells out.

Given the fact that the Debian package update took away the problem, I
ended up thinking that it was grep badly behaving with the -v flag. But
I have no clues about that.

Best,
Stefano


-- 
Stefano Costa
steko at jabber.linux.it
http://www.iosa.it Archeologia e Software Libero
Io uso Debian GNU/Linux!