Is it possible to generate an example string based on a regex pattern?

Question

In my application the user can enter his own regex pattern into a text box so he can force a certain input for another user/text box. Is it possible for the user to see an example of a string that would match the regex he has entered? For example if he was to enter: ^[A-Z]{2}$, it would generate a string like "XX" to show the user he can only enter two capital letters.

If there's no easy way to accomplish this (and I assume there isn't), how difficult would it be to build? Or does something like this already exist?

see http://stackoverflow.com/questions/205411/random-string-that-matches-a-regexp, it may help you. — Shimrod, Jun 28 '10 at 09:25

score 8 · Accepted Answer · edited Jul 28 '15 at 08:46

8

Check out Xeger. It looks like it can do what you want. It's in Java though.

Here is an example from the test suite:

   @Test
    public void shouldGenerateTextCorrectly() {
        String regex = "[ab]{4,6}c";
        Xeger generator = new Xeger(regex);
        for (int i = 0; i < 100; i++) {
            String text = generator.generate();
            assertTrue(text.matches(regex));
        }
    }

Update: thanks to Nikos Baxevanis, the dk.brics.automaton have been ported to C# at https://github.com/moodmosaic/Fare

edited Jul 28 '15 at 08:46

Veverke

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answered Jun 28 '10 at 09:33

Martin Wickman

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That's exactly what I'm looking for.. but for C#. At least I have something I can use as reference. – Fusyion Jun 28 '10 at 09:39
Xeger is just a thin wrapper around http://www.brics.dk/~amoeller/automaton/ which is DFA/NFA implementation of some regexp operations. Maybe there is something like that available for C# somewhere? – Martin Wickman Jun 28 '10 at 09:52
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@MartinWickman Yes, both the dk.brics.automaton and the xeger sources have been ported to C# at https://github.com/moodmosaic/Fare – Nikos Baxevanis Nov 08 '12 at 18:14

score 8 · Answer 2 · edited May 23 '17 at 10:29

8

For C# you may also want to look at project Fare. For more details have a look at this answer.

Example

var regex = @"((mailto\:|(news|(ht|f)tp(s?))\://){1}\S+)";
var xeger = new Xeger(regex);

var result = Regex.IsMatch(xeger.Generate(), regex);
// -> Prints 'true'

edited May 23 '17 at 10:29

Community

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answered Nov 23 '11 at 10:43

Nikos Baxevanis

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Nikos, it would be very useful if you show a code sample using Fare – Alberto Montellano Aug 18 '14 at 15:57
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Alberto, I just added an example. Hope that helps. – Nikos Baxevanis Aug 18 '14 at 19:54

score 0 · Answer 3 · answered Apr 23 '14 at 12:11

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I once needed such thing too, so I created a simple program with gui using xeger lib mentioned above. Simply run .jar from dist folder (jre is required) https://github.com/ogyct/SampleFromRegex

answered Apr 23 '14 at 12:11

Dmitry Avgustis

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Is it possible to generate an example string based on a regex pattern?

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