I have the text:
This is a test. This is only a test! If there were an emergency, then Information would be provided for you.
$ cat <FILE> | perl -pe 's/[\s.?!]/\n/g;'
You can use this gnu grep command to extract first after each period or
grep -oP '(?:^|[.?!])\s*\K[A-Z][a-z]*' file This This If
Though I must caution you may get false results for cases like
(?:^|[.?!])- match start or DOT or
\s*- match 0 or more whitespaces
\K- match reset to forget matched data
[A-Z][a-z]*- match a word startign with upper case letter