Win8 Strawberry 5.30.3.1 (64)  Sun 07/17/2022 22:13:06
C:\@Work\Perl\monks\abdan
>cat story.rst
seen first
the first found
found second
seen second
first occurred
occurred second

>perl -ane "print if /(seen|found|occurred)/ && !$seen{ $1 }++" story.rst
seen first
the first found
first occurred