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I was posed an interesting question from a colleague for an operational pain point we currently have, and am curious if there's anything out there (utility/library/algorithm) that might help automate this.
Say you have a list of literal values (in our cases, they are URLs). What we want to do is, based on this list, come up with a single regex that matches all of those literal items.
So, if my list is:
http://www.example.com
http://www.example.com/subdir
http://foo.example.com
The simplest answer is
^(http://www.example.com|http://www.example.com/subdir|http://foo.example.com)$
but this gets large for lots of data, and we have a length limit we're trying to stay under.
Currently we manually write the regexes but this doesn't scale very well nor is it a great use of anyone's time. Is there a more automated way of decomposing the source data to come up with a length-optimal regex that matches all of the source values?
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A regular expression (regex, regexp or rational expression) is a sequence of characters that specifies a search pattern. Usually these patterns are used by string-searching algorithms for find or find and replace operations on strings, or for input validation.
If you want to match for the actual '+', '. ' etc characters, add a backslash( \ ) before that character. This will tell the computer to treat the following character as a search character and consider it for matching pattern. Example : \d+[\+-x\*]\d+ will match patterns like "2+2" and "3*9" in "(2+2) * 3*9".
This operator is similar to the match-zero-or-more operator except that it repeats the preceding regular expression at least once; see section The Match-zero-or-more Operator ( * ), for what it operates on, how some syntax bits affect it, and how Regex backtracks to match it.
The Aho-Corasick matching algorithm constructs a finite automaton to match multiple strings. You could convert the automaton to its equivalent regex but it is simpler to use the automaton directly (this is what the algorithm does.)
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