Regular expression listing all possibilities

Question

Given a regular expression, how can I list all possible matches? For example: AB[CD]1234, I want it to return a list like: ABC1234 ABD1234

I searched the web, but co

Answer 1

It may be possible to find some code to list all possible matches for something as simple as you are doing. But most regular expressions you would not even want to attempt listing all possible matches.

For example AB.*1234 would be AB followed by absolutely anything and then 1234.

Answer 2

I'm not entirely sure this is even possible, but if it were, it would be so cpu/time intensive for many situations that it would not be useful.

For instance, try to make a list of all matches for A.*Z

There are sites that help with building a good regular expression though:

• http://www.fileformat.info/tool/regex.htm
• http://www.regular-expressions.info/javascriptexample.html
• http://www.regextester.com/

Answer 3

It's possible to write an algorithm to do this but it will only work for regular expressions that have a finite set of possible matches. Your regexes would be limited to using:

• Optional: ?
• Characters: . \d \D
• Sets: like [1a-c]
• Negated sets: [^2-9d-z]
• Alternations: |
• Positive lookarounds

So your regexes could NOT use:

• Repeaters: * +
• Word patterns: \w \W
• Negative lookarounds
• Some zero-width assertions: ^ $

And there are some others (word boundaries, lazy & greedy quantifiers) I'm not sure about yet.

As for the algorithm itself, another user posted a link to this answer which describes how to create it.

Answer 4

Well you could convert the regular expression into an equivalent finite state machine (is relatively simple and can be done algorithmly) and then recursively folow every possible path through that fsm, outputting the followed paths through the machine. It's neither very hard nor computer intensive per output (you will normally get a HUGE amount of output however). You should however take care to disallow potentielly infinite passes (like .*). This can be done by having a maximum allowed path length, after which the tracing is aborted

Answer 5

A regular expression is intended to do nothing more than match to a pattern, that being said, the regular expression will never 'list' anything, only match. If you want to get a list of all matches I believe you will need to do it on your own.

Answer 6

Exrex can do this:

$ python exrex.py 'AB[CD]1234'
ABC1234
ABD1234