reverse grep

Erik Trulsson ertr1013 at
Sat Nov 3 17:29:08 PDT 2007

On Sun, Nov 04, 2007 at 01:12:45AM +0100, deeptech71 at wrote:
> How is it possible to select lines that do NOT match a specific pattern?

By using the '-v' option to grep.

> For example, I'm connecting to via telnet (port 23), and do 
> tcpdump -nli rl0. This cyclic traffic, becuase when tcpdump outputs 
> something, the system sends me some packets, which generates output in 
> tcpdump, and vice versa. I want to filter out packets of telnet access to 
> the FreeBSD machine, that is, something like:
>     tcpdump -nli rl0 | grep --non-matching-lines

You can also tell tcpdump directly to not generate certain output.
E.g.  'tcpdump -nli rl0 not port 23' will not display any traffic to/from
port 23.  Read the tcpdump(1) manpage for the details - many more options
are available.

<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at

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