Perl one liner to delete or replace a line in a file

Delete a matching line from a file:

perl -ni -e 'print unless /pattern/' filename

Replace a matching pattern to another:

perl -pi -e "s/matchingpattern/newpattern/" filename

Remove duplicate lines:

 perl -i -ne 'print unless $seen{$_}++' filename 

Perl options:

-n: while (<>) { ... # your script}
-p: while (<>) { ... # your script } continue { print or die "-p destination: $!\n";}
-i: in place