I use regular expressions to validate user input. Now I can configure the regex and so it would help the user to see an example of how a certaint input has to be formatted.
Is it possible to generate some strings that match an arbitrary regex? And is there even an implementation usable somewhere?
UPDATE: Due to the licence I can not use REX. Are there other possiblities?
Try using this app Rex can do this :)
http://research.microsoft.com/en-us/projects/rex/
For java it's https://code.google.com/p/xeger/
So there are many regex matches generators :)
And this: https://github.com/moodmosaic/Fare
It's xeger wrapper in c#
Some solutions:
(1) If the regex is written by you (not by the user) and rarely changes, why create anything programmatically? You could just create a few nice examples by hand.
(2) Use a ready-made solution. (see other answers)
(3) Rejection sampling, the sledge hammer solution to all random generation problems: Create a random string and check if it matches the regex. If not, try again. If the regex is very specific, this solution has terrible performance, though.
(4) Implement a parser that transforms a regex into a string construction tree that consists e.g. of the nodes below. Every node has a CreateRandomString method that follows certain rules. Creating a random string means calling that method for the root node.
concatenation: Traverse all child subtrees and concatenate the results in order.
random choice: Select a random child subtree and traverse it. Return the result.
multiplication: Create a random number n between a and b. Traverse the subtree n times and concatenate the results.
leaf: Return a constant string.
Creating the parser is the tricky part :) , especially nested structures. (I have written one for a syntax similar to regexes.)
as specified in comment, Rex tool will do the trick -
Using Rex to create strings that match your pattern:
run the rex.exe as follows:
rex.exe "your_regex_pattern_here" /k:your_required_examples_num_here
more info regarding this:Rex Guide
Almost certainly not, no.
Regular expressions are generally used, in the context you're looking at, to check that a string matches a given format. If you know what your format should be well enough that you're writing a regular expression for it, there should be no reason why you can't generate your own test data easily enough.
[Edit - it appears there are a few examples around. But this does ignore the fact that, to test that your regex is correct, you must have written test data already. So you should already have your strings.]
Some random matchessection. You may be surprised with the propositions made when your regex starts to be complicate..*?