Bash script to generate knock sequences

Here is a simple bash script to generate random knock/knockd sequences with desired length, port ranges and types:

#!/bin/bash

# ---- config.
knocks_number=5
knocks_types=('udp' 'tcp');

port_min=1000
port_max=2000

# ---- config end

dport=$(( $port_max - $port_min ))

for i in `seq 1 $knocks_number`
do
    sequence=$sequence$[`shuf -i $port_min-$port_max -n 1` ]":"${knocks_types[ $[($RANDOM % 2)] ]}","
done

echo
echo "# A sequence for knockd.conf:"
echo "sequence = $sequence" | sed 's/,$//g'
echo "# A sequence to use with knock"
echo "knock \$ADDRESS $sequence" | sed 's/,/ /g'

The output may looks like:

# A sequence for knockd.conf:
sequence = 1460:udp,1344:tcp,1997:tcp,1712:udp,1304:udp
# A sequence to use with knock
knock $ADDRESS 1460:udp 1344:tcp 1997:tcp 1712:udp 1304:udp