we had a similar question not long ago: Using special characters in left part of a regex match?

In short: It's not easy!!!

I'm not sure how efficient it is but I might try to code all possibilities into a long or-clause

/(12345x|1234x6|123x56|123x6| ...)/

please note that from 5.10 on such expressions are efficiently trie-optimized.

Another approach could be to match all "x" and surrounding n bytes to be further investigated...

edit

something like /(1 [2-5]{0,4} x [2-5]{0,4} 6)/gx in a while loop to narrow the set of possible matches.

Cheers Rolf

( addicted to the Perl Programming Language)

In reply to Re: "Inverse" Pattern Matching by LanX
in thread "Inverse" Pattern Matching by hdb

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