It should be as simple as adding a variable to the end of your regexp.
$ set comment “this is an aop type comment”
$ regexp {(tba|TBA|aop|AOP)} $comment output
$ 1
$ puts $output
$ aop
This is assuming you don’t want the – / or blank space returned. You may also want to drop the ^ and $ from your regexp unless the string will only contain one of the four values.
Hope this helps.
Steve