$ cat foo
Hello world, this is
a paragraph.

This is also a paragraph
but it contains doubled
doubled words.
$ grab 'x/[^\n].+?(?=\n\n|$)/ g/(\b\w+\b)\s+\1/' foo
This is also a paragraph
but it contains doubled
doubled words.
$ # Just like grep, you can display match positions
$ grab -f '…' foo
foo:4:1:This is also a paragraph
but it contains doubled
doubled words.