On Thu, Aug 25, 2011 at 12:02:37PM +0200, Honza Mach wrote:
> Hi,
>
> On Thu, 2011-08-25 at 11:35 +0200, Paul Johnson wrote:
> >
> > say "extracted: ", /^(\d+\s+.{$len})/ if ($len) = /^(\d+)/
> > Sometimes two passes are are better than one.
> >
>
> Thank you for your advice, however I wanted to do it in one pass because
> of the following reasons:
>
> 1. I wanted to compile the pattern because of the performance
Ah. Then you have already benchmarked a solution, found it to be too
slow, profiled your code and discovered that this section of the code
was the bottleneck in such a way that compiling the regualar expression
would solve the problem?
Why on earth are you worried about performance? Especially when your
data is coming from a socket. I suggest not worrying about performance
until you need to.
Please don't think I'm geting at you personally here. Perhaps you have
already done this. But in general there is far too much talk about
speed on this list. Make your code correct. Make it nice. Until that
point performance cannot be a concern.
> (I guess it is not possible to compile the pattern, when there are
> some substitutions of the variables from outside of the RE engine,
> or am I wrong?)
See below.
> 2. Perhaps I should have mentioned, that the application is parsing the
> continuos string stream coming from a socket, there are many of
> these "commands" coming one after each other and there will not
> always be the complete command present in the buffer, next chunk
> may come later. I was actually trying to use it this way:
>
> my $string = "5 abcde 2 fg 3 hij 6 klm";
> while ($string =~ s/\s*(\d+)\s+(.{\1})//)
> {
> print "extracted: $1 $2\n";
> }
>
> This way the while loop elegantly fails, when the pattern does not
> match and when the next data arrives, the check is made again.
OK. So try this:
say "extracted: $1 $2" while s/\s*(\d+)(?{$len = $^N})\s+((??{"." x $len}))//
That uses features marked as experimental. It would probably be a good
idea to read perlre to understand them. You can even compile that if
you want to but I'm not sure what difference, if any, you will notice in
doing so.
> I was just trying to find the most elegant solution, but if it is not
> possible, I will create some work around, that is not the problem.
Some might class this as an elegant solution. Others might take the
opposite position.
Good luck,
--
Paul Johnson - p...@pjcj.net
http://www.pjcj.net
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