Find string patterns preferably in regex for string streams
The general approach is likely to be:


Identify a set of candidate patterns that might appear.
For each candidate pattern, check for all instances of that pattern.


I'm not aware of any simple procedure that avoids the need for step 1.  The problem is that there are many possible patterns that might appear (e.g., "consists solely of Latin-8 characters"; "length is always at most 100") but most of them won't be meaningful or useful in your domain.  Only you know what will be meaningful/useful.  So, you'll have to use your domain knowledge to identify which potential patterns are useful -- I don't know of any algorithm that can do that for you.