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Re: backreferences

On 10/16/2015 05:35 AM, Bart Schaefer wrote:
} when nested and even when 'doing something else'?


Ok, good to know. I've only been using backreferences since two days ago and up till now it's seemed that you had to add parentheses to create the reference and existing parentheses only had their existing syntax. I suppose this means that when you do have existing parentheses you'll get a 'match' whether you want one or not but so what, just ignore it. Yup, that's best.
... but the part about not needing the
middle * is wrong, because (^edcba) matches xxxxedcbaxxxx just fine, and
I assume you don't want that.

   test2 ()
   # Bart doesn't like:
   #if [[ "$sstring" = (#b)([(^(edcba))]*)(edcba)(*) ]];
   # Bart likes:
   if [[ "$sstring" = (#b)(^edcba)(edcba)(*) ]];

      echo "\nIt's a poyfect match\n"

   echo "one   $match[1]"
   echo "two   $match[2]"
   echo "three $match[3]"
   echo "four  $match[4]"
   echo "five  $match[5]"

   It's a poyfect match

   one   abcde
   two   edcba
   three abcde

... match[1]  seems to agree with your previous interpretation, no?

This needs to be (#b)(^edcba*)(edcba)(*)

That produces identical output as well, so what's the diff? Probably one of those things that blows up in your face one day ...
} God knows.  But your simplified command works fine too, and I'll
} take it on faith.  I've never seen any sort of 'any number of characters'
} sort  of thing look other than:
} [....]*

No, now you're confusing grep-style regular expressions with zsh patterns.

... which is what I meant to say.
     .		?
     .*		* or ?#
     .+		?##
     .?		(?|)
     [xyz]	[xyz]
     [xyz]*	[xyz]#

There's a lot more but those are the most important bits.

A table like that is worth tattooing onto one's arm. Seriously once a fella has learned a bit of regex it becomes burnt into the brain, and it's an act of deliberation to use the other syntax. It sorta makes it worse that they are similar :( Is a complete table available somewhere?
} ... so you can see where I'd go astray there.  Ok, so
} ^(edcba)
} is individual character matches and
} (^edcba)
} is  anything up to "edcba"

No.  [^edcba] is individual character matches and (^edcba) is anything
other than the literal string edcba,

Ok, got it. A mortal's guide to this stuff would sure be useful. All the docs tend to dive right in to the deep end and immediately start explaining all the possible obscure permutations when KSH_GLOB is set and it's not leap year but it IS a Friday. Such control! But we start with the basics.
including longer strings that have
edcba as a substring.  Negated patterns are really tricky.


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