I think you can imagine I'm not going to talk about the police dog…
Rex is a utility designed by a team of Microsoft Research. It allows to generate strings that match a regular expression. Results can be saved to a file for easy use. An example of use:
> rex.exe "^[a-z]+$" /k:10 /file:toto.txt
/k:10generates 10 results
/file:toto.txtsave results to a file
For instance, here's the generated strings:
d ux gxh k lo ze m jvl u som
Rex makes it very convenient to generate data for testing. In addition it is a .NET executable file, so it is possible to use it in your own applications.