> For some regexes, it is very easy, for others, it is very difficult or even impossible.

it's often much simpler as you might think, cause you can decompose regexes into smaller and easier parts.

 perl -e'use re 'debug';qr/x{100}.*y{100}/'
Compiling REx "x{100}.*y{100}"
Final program:
   1: CURLY {100,100} (5)
   3:   EXACT <x> (0)
   5: STAR (7)
   6:   REG_ANY (0)
   7: CURLY {100,100} (11)
   9:   EXACT <y> (0)
  11: END (0)
anchored "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"... at 0 floating "yyyyyyyyyy
+yyyyyyyyyyyyyyyyyyyy"... at 100..2147483647 (checking floating) minle
+n 200 
Freeing REx: "x{100}.*y{100}"

[download]

In this case you start looking for 'x'x100 in a sliding window of size >200 from the beginning. Then you search backwards from the end in sliding windows for 'y'x100.

Like this even greedy matches can be handled (mostly) and the total match might even cover terrabytes.

Cheers Rolf

( addicted to the Perl Programming Language)

In reply to Re^5: Possible to have regexes act on file directly (decompose regex) by LanX
in thread Possible to have regexes act on file directly (not in memory) by Nocturnus

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