How do I get the number of (currently) established TCP connections for a specific port?

How do I get the number of (currently) established TCP connections for a specific port?

I have managed to get counters for traffic working by doing i.e for outgoing RTMP.

iptables -N $CHAIN 
iptables -I OUTPUT -j $CHAIN
iptables -A $CHAIN -p tcp --sport 1935
iptables-save

But now i need the number of current (not a counter) connections, for each protocol

I can get the total number with: netstat -ant | grep ESTABLISHED | wc -l

Can anyone help? Im not an iptables guru.

You say you're not a guru, but which of us is? You've done most of the heavy lifting; I'm sure the rest will occur to you in a minute or two.

Until then, try netstat -an|grep ESTABLISHED | grep -w 1935.

It works for me:

# netstat -ant | grep ESTABLISHED | wc -l

output:

total connection 22....

netstat + grep is a good and simple option for a few connections but if you have a huge number of connections I would recommend ss as recommended in nixCraft.

For instance: ss -s

Total: 78 (kernel 79)
TCP:   31 (estab 27, closed 0, orphaned 0, synrecv 0, timewait 0/0), ports 16

Transport Total     IP        IPv6
*     79        -         -        
RAW   0         0         0        
UDP   4         2         2        
TCP   31        2         29       
INET      35        4         31       
FRAG      0         0         0