Let's just make the final count with awk too...
#!/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.
netstat -an |
awk -v date="$(date)" '$6 == "ESTABLISHED" && /:8333/ { split($5, a, ":"); print a[1] ; n++ }
END { print "# " date " : " n " bitcoin clients seen." }'
Just to be a little bit picky, the netstat output is slightly different between BSD-like Unix and GNU/Linux.
The port is separated by a dot on the BSD-like Unix. So maybe the pattern matching /:8333/ could be
reviewed to include also the other output... but beside that, this is just fine.