#37 -lp doesn't not act like original

[Anonymous]

Fedora 7
The original netcat allows this:

nc -lvnp 31000 127.0.0.1 > x

The man page says this should work:

SYNOPSIS
netcat [options] hostname port [port] ...

netcat -l -p port [options] [hostname] [port] ...

However, GNU netcat does this:
$ nc -lvnp 31000 127.0.0.1 > x
nc: cannot use -p and -l

[Denis Vlasenko]

I second that.

GNU nc broke command-line compatibility with original nc-1.10 needlessly.
This causes PITA for anyone trying to use nc -l from scripts.

With -l, local port used to be specified with -p:

nc-1.10:
# ./nc -vvv -l -p 1111
listening on [any] 1111 ...

Not in GNU nc:
# nc -vvv -l -p 1111
usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]

GNU nc requires it to be specified like this:
# nc -vvv -l 0.0.0.0 1111
(waits for connections)

[Note that the second buglet is here - despite -vvv nothing like "listening on [any] 1111 ..." is printed]

This format (nc -vvv -l 0.0.0.0 1111) was accepted by original nc,
but had completely different meaning! It meant "listen on random port
(because -p NNN is missing), and accept only connections from
0.0.0.0 1111":

# ./nc -vvv -l 0.0.0.0 1111
0.0.0.0: inverse host lookup failed:
listening on [any] 46000 ...

Original's interpretation of parameters is more consistent:

nc ... [-l] [-s LOCAL_IP] [p LOCAL_PORT] [REMOTE_IP] [REMOTE_PORT]

whereas GNU nc has something like

nc ... -l LOCAL_IP LOCAL_PORT
or
nc ... -l REMOTE_IP REMOTE_PORT

Help text isn't too obvious about it:
# nc
usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]

[Denis Vlasenko]

In previous comment, I meant:

nc ... -l LOCAL_IP LOCAL_PORT
or
nc ... REMOTE_IP REMOTE_PORT

[Giovanni Giacobbi]

I'll investigate this problem.