#!/bin/sh
# Display foreign IP addresses coming from port 8333 --or-- connected to local port 8333.
# Append line at end with date and count of addresses displayed.
#
# GNU Linux netstat separates port numbers from IP addrs using colon ':',
# whereas BSD netstat separates them using a period '.'.  The sed line
# below converts the BSD '.' to a ':', to make it easier for awk to
# split off the port.

netstat -an |
    sed 's/\([0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\)\.\([0-9][0-9]*\)/\1:\2/g' |
    awk -v date="$(date)" '
        $6 == "ESTABLISHED" && /:8333/ { split($5, a, ":"); print a[1] ; n++ }
        END { print "# " date " : " n " bitcoin clients seen." }
    '