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Date:      Fri, 24 Jan 2014 10:34:47 -0700 (MST)
From:      Warren Block <wblock@wonkity.com>
To:        "'Devin Teske'" <dteske@FreeBSD.org>
Cc:        'RW' <rwmaillists@googlemail.com>, freebsd-questions@freebsd.org
Subject:   RE: awk programming question
Message-ID:  <alpine.BSF.2.00.1401241029230.89161@wonkity.com>
In-Reply-To: <050a01cf1929$051c0670$0f541350$@FreeBSD.org>
References:  <F01EB9CE742DEB17DB6B51C7@localhost> <alpine.BSF.2.00.1401230900270.76961@wonkity.com> <20140123185604.4cbd7611@gumby.homeunix.com> <04a201cf1878$8ebce540$ac36afc0$@FreeBSD.org> <alpine.BSF.2.00.1401231346520.80613@wonkity.com> <04aa01cf187e$cfcf9ef0$6f6edcd0$@FreeBSD.org> <alpine.BSF.2.00.1401231537260.80613@wonkity.com> <04d201cf1895$20956890$61c039b0$@FreeBSD.org> <alpine.BSF.2.00.1401231904410.82598@wonkity.com> <050a01cf1929$051c0670$0f541350$@FreeBSD.org>

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On Fri, 24 Jan 2014, dteske@FreeBSD.org wrote:

>>> I'm not entirely sure how I feel about that -- in terms of
>>> readability, I'm not sure if the following is more readable:
>>>
>>> 	/(a[^z]*z)/
>>
>> Wait till you see the other PCRE stuff.  There are lots of things 
>> that really make it much more powerful.  perlre(1) covers it all, 
>> sketchily and not really in order.
>>
>> I've said elsewhere, and will repeat again: "Mastering Regular 
>> Expressions" by Jeffrey E. F. Friedl (the owl book) is amazing.  My 
>> first edition (1997) does not have some of the newer Perl stuff, but 
>> it's now up to a third edition:
>>
>> http://shop.oreilly.com/product/9780596528126.do
>
> Does it cover "back references" ? Definitely one of the more powerful 
> but esoteric regular expressions (e.g., you want to match a string 
> that starts with a quote and has a matching terminating quote, but not 
> match a string that has a quote without matching termination).

It does cover backreferences, in the sense of egrep:
\<[A-Za-z]+) +\1\>

That will find a word followed by one or more spaces and the same word 
again.

> If-so, I'm totally buying that book.

Buy it.  I've never seen another book that treats such a complex subject 
with such clarity and readability.



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