Build a hash of the words to eliminate duplicates and sort the keys to order the output. (No shell required:)
Update: I forgot the lowercase requirement.
perl -nle"$words{lc$1}=undef while m[(\w+)]g; END{ print for sort keys
+ %words }" <textfile
(Use single quotes instead of double as needed)
Examine what is said, not who speaks.
1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
3) Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clarke.