perl -ne '$x=/ou/..0; print if $x && $x-1 <= 3' data.dat

##</code><code>##

% cat data.dat
one
two
thrtestee
four
five
six
werwr
werwer
seen?

% perl -ne '$x=/ou/..0; print if $x && $x-1 <= 3' data.dat

four
five
six
werwr