Yes, i got fixed with this and i made unsuccesfull tries using eof..eof flip-flop to process even files..
anyway now i get two semi-obfuscated oneliners, the first, simpler, is called with a single arg (the name of file):

# $y is <C>yet</C> set for the second read, @u is <C>unwanted</C> <P>

perl -lnE "BEGIN{push @ARGV,$ARGV[0]}eof&&!$y?$y=close ARGV:/XXXXX/&&!
+$y?push @u,$.-1..$.+1:$y&&!($.~~@u)?say:0" next-and-previous.txt
11111
22222
33333
44444<P>
[download]

while the latter is parametrizable one: firts arg is the regex used to match unwanted strings, the second is the number of lines to be removed after and before and then the filename:

perl -lnE "BEGIN{$r=shift;$r=qr/$r/;$n=shift@ARGV;push @ARGV,$ARGV[0]}
+eof&&!$y?$y=close ARGV:/$r/&&!$y?push @u,$.-$n..$.+$n:$y&&!($.~~@u)?s
+ay:0" XXXXX 1 next-and-previous.txt
11111
22222
33333
44444

perl -lnE "BEGIN{$r=shift;$r=qr/$r/;$n=shift;push @ARGV,$ARGV[0]}eof&&
+!$y?$y=close ARGV:/$r/&&!$y?push @u,$.-$n..$.+$n:$y&&!($.~~@u)?say:0"
+ XXXXX 2 next-and-previous.txt
22222
[download]

I promise i'll try to no bother you anymore with this.. :=)

update the parametrized oneliner can be shortend using -s switch (that has some problem anyhow) It is the second time i use -- too.

perl -slnE "BEGIN{$r=qr/$r/;push @ARGV,$ARGV[0]}eof&&!$y?$y=close ARGV
+:/$r&&!$y?push@u,$.-$n..$.+$n:$y&&!($.~~@u)?say:0"  
           -- -r=XXXXX -n=1 next-and-previous.txt

11111
22222
33333
44444
[download]

L*