A small note:
if you run regex you will see, you need to improve the formula into a non-infinite string.
Also you must limit the total size of the string, with minimum and maximum bounds.
Then, to round it all up, you need to specify not only the grep-position, but it would be nice to define the frequency range for each letter as well.
All that does not fit in a Regex expression, because it is designed & intended for checking a string / pattern matching.
Not for implementation and creation of a grouped string.
if you run regex you will see, you need to improve the formula into a non-infinite string.
Also you must limit the total size of the string, with minimum and maximum bounds.
Then, to round it all up, you need to specify not only the grep-position, but it would be nice to define the frequency range for each letter as well.
All that does not fit in a Regex expression, because it is designed & intended for checking a string / pattern matching.
Not for implementation and creation of a grouped string.