From: Robert Klemme <bob.news@...>
Date: 2004-08-17T16:55:58+09:00
Subject: Re: Rubish Way of extracting elements


"Daniel V�lkerts" <dvoelkerts@web.de> schrieb im Newsbeitrag
news:cfr4ml$d13$00$1@news.t-online.com...
> Robert Klemme wrote:
>
> > Some more admittedly ugly constructions:
> >
> > val = "<165> Aug 16 17:01:35 localhost Just a test"

(1) This one converts the RX MatchData into an array and tests for emptyness
to determine whether it matched.  And along the way values are assigned to
local vars.

> > unless ( ( pri, timestamp, device, msg = * /^<(\d+)> \s+ (\S+ \s+ \d+
\s+
> > \d+:\d+:\d+) \s+ (\S+) \s+ (.*)$/x.match(val).to_a ).empty? )
> >   puts "matched"
> > end

(2) Similar, but now just one local var is used as match check: if "pri" is
not nil, the RX matched.

> > pri, timestamp, device, msg = * /^<(\d+)> \s+ (\S+ \s+ \d+ \s+
\d+:\d+:\d+)
> > \s+ (\S+) \s+ (.*)$/x.match(val).to_a
> > if pri
> >   puts "matched"
> > end

(3) Same approach as (1) but the regexp is defined as a constant to make
stuff more readable.

> > LOG_RX = /^<(\d+)> \s+ (\S+ \s+ \d+ \s+ \d+:\d+:\d+) \s+ (\S+) \s+
(.*)$/x
> >
> > unless ( ( pri, timestamp, device, msg = *
LOG_RX.match(val).to_a ).empty? )
> >   puts "matched"
> > end

(4) Similar approach to (2) but the test is included ("&& line").  Note that
this time no conversion to array is done here so we need the additional
local "line" to receive the complete capture.

> > if ( line, pri, timestamp, device, msg = * /^<(\d+)> \s+ (\S+ \s+ \d+
\s+
> > \d+:\d+:\d+) \s+ (\S+) \s+ (.*)$/x.match(val) ) && line
> >   puts "matched"
> > end

(5) Same as (4) but with regexp in constant as in (3).

> > if ( line, pri, timestamp, device, msg = * LOG_RX.match(val) ) && line
> >   puts "matched"
> > end
> >
> > :-)
> >
> >     robert
> >
>
> *boom* That blow my mind away! No no, thanks a lot for that piece of code.

:-)  I *should've* put some comments in...  Ok, inserting them above now.

> But I prefer the scanf and one-line-regexp.

Basically I used extended regular expressions (switched by the "/x" flag).
Whitespace is ignored, that's why you see more "\s+" in there.  And that's
why the regexp is longer.

> I'll test which kind performs better for my needs. As I said, I'm a ruby
> newbie and personal programming rule is: keep it simple! ;) I've to
> understand the things I wrote.

That's an excellent road to walk down!  Handcrafted, simple code is better
than a mindless copy of something found somewhere.

Kind regards

    robert