#!/usr/bin/perl
use warnings;use strict;

foreach (<DATA>)  {
  s{
    (^|\.)      # Start of string, or last full-stop
    (.*?)       # Non-alpha characters (non-greedy)
    ([a-zA-Z])  # First alphabetic character
    ([^\.]*)    # Through to next full stop
  }{
      $1.$2.uc($3).lc($4)
  }gex;

  print;
}
__DATA__
today is wednesday.tomorrow IS THURSDAY.
I am trying to write a regex to convert the first letter and any letter following a full stop in a string to uppercase .and  .   all the other characters to lowercase.