regex search valid only if registers n and n+1 are equal?

Voronich has asked for the wisdom of the Perl Monks concerning the following question:

Help me obi-several, you're my only hope.

I'm not confident I phrased that right in the title. But here 'goes. (I know this is out there but I don't have any hooks on what to call it to search.)

I have 2 strings:

"foo 1000 bar 1000"
"foo 1000 bar 500"

and I'm starting with something like:

/foo (\d+) bar (???)/

My goal is to match the first string but not the second. I couldn't care less what the values are, merely whether or not they are equal.

I seem to recall it being possible (and perhaps fundamental) to match against "the string that matched grouping N".

But for the life of me I can't figure out how to do it, or what kind of keywords to search for to dig this up.

(please feel invited to edit this for clarity.)

UPDATE: Damnit. My fault. There's an additional restriction. The regex itself is to be included in a fairly obtuse dispatch mechanism so the test needs to be constrained entirely to the matching of the expression. (does that make sense?)

Here's another wrinkle for the willing: Given that I can match easily enough with backrefs those two numbers, anyone know how to, again entirely within the scope of the regex match, return a POSITIVE match if the two numbers (both of \d+ format) do NOT match? (Yes, this is a practical independent real-world case. Ah, the joys of parsing log files in realtime.)

Thanks very much for your help (this article pushes me up to Monk! *SQUEE*)

-V

uccu

Comment on regex search valid only if registers n and n+1 are equal? Download Code

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Re: regex search valid only if registers n and n+1 are equal? by Hue-Bond (Priest) on Jun 30, 2006 at 19:36 UTC
Use backreferences, like this: `while (<DATA>) { print "match on $1\n" if /^\S+ (\d+) \S+ \1$/; } __DATA__ foo 1000 bar 1000 foo 1000 bar 500` [download] -- David Serrano	[reply] [d/l]
Re^2: regex search valid only if registers n and n+1 are equal? by Voronich (Hermit) on Jun 30, 2006 at 20:17 UTC
yeesh. "backreference" is the word that unlocked the universe here. Thanks :) http://www.mpwilson.com/uccu/	[reply]
Re: regex search valid only if registers n and n+1 are equal? by TedPride (Priest) on Jul 01, 2006 at 01:08 UTC
Why make things overly complicated? `while (<DATA>) { next if !m/foo (\d+) bar (\d+)/ \|\| $1 != $2; print; } __DATA__ foo 1000 bar 1000 foo 1000 bar 500` [download]	[reply] [d/l]
Re^2: regex search valid only if registers n and n+1 are equal? by ikegami (Patriarch) on Jul 01, 2006 at 04:21 UTC
That can also be written using positive logic, as follows: `while (<DATA>) { print if m/foo (\d+) bar (\d+)/ && $1 == $2; } __DATA__ foo 1000 bar 1000 foo 1000 bar 500` [download]	[reply] [d/l]
Re^3: regex search valid only if registers n and n+1 are equal? by antirice (Priest) on Jul 01, 2006 at 06:26 UTC
Hello De Morgan's laws. Yes, I think you already knew what it is. This is for the other members of the audience.	[reply]
Re: regex search valid only if registers n and n+1 are equal? by Miguel (Friar) on Jul 01, 2006 at 12:23 UTC
~~Just another way:~~ UPDATE: Another 3 ways: `#!/usr/bin/perl use strict; use warnings; while (<DATA>) { # 1 # my @arr = split; # print if $arr[1] != $arr[3]; # 2 print if sub { $_[1] != $_[3] }->(split); } # 3 # while (@_ = <DATA> =~ /(\w+)\s+/g) {print "@_\n" if $_[1] != $_[3]} __DATA__ foo 1000 bar 1000 foo 1000 bar 500` [download] Prints: `foo 1000 bar 500` [download]	[reply] [d/l] [select]
Re: regex search valid only if registers n and n+1 are equal? by gam3 (Curate) on Jul 01, 2006 at 15:01 UTC
And here is a benchmark for the 3 solutions. It seems that using the regular expression natively is very fast. This is followed by the regular exprssion and OR logic. The split is slowest. Read more... (1353 Bytes) `Rate split simple backref split 4329/s -- -31% -66% simple 6313/s 46% -- -50% backref 12658/s 192% 101% --` [download] UPDATE: As Sam points out I had the effeciency of the different techniques completely backwards. I also noticed a bug in the simple technique. Fixxing that speed it up by 50%. -- gam3 A picture is worth a thousand words, but takes 200K.	[reply] [d/l] [select]
Re^2: regex search valid only if registers n and n+1 are equal? by samtregar (Abbot) on Jul 01, 2006 at 16:10 UTC
The backreference is much slower as you would expect. Really? Looks like the backreference is faster in your test. -sam	[reply]
Re: regex search valid only if registers n and n+1 are equal? by sh1tn (Priest) on Jun 30, 2006 at 23:19 UTC
Another possible solution can be: `while (<DATA>) { print "match on $1 and no 2nd$2\n" if /\S+ (\d+) \S+ (?:\d+)/; }` [download]	[reply] [d/l]
Re^2: regex search valid only if registers n and n+1 are equal? by ikegami (Patriarch) on Jul 01, 2006 at 04:19 UTC
I get two prints (as expected) for the provided data. It should only print the first line. Perhaps you didn't understand the question?	[reply]