Bash script to test port availability

Ahmed Aboulnaga -

I created a quick script to test if a port is consistently available between a source server to a target server for the purpose of gathering statistics to see if there are any network hiccups not.

This is a very simple and straightforward script.

Simply copy the content below to a file called test_network_port.sh and change the permissions (e.g., chmod 700 test_network_port.sh):

#!/bin/bash

#--------------------------------------------------------------#
# FILENAME:      test_network_port.sh                          #
# CREATION DATE: 2021-12-06                                    #
# DESCRIPTION:   Test network port to IP:PORT                  #
# AUTHOR:        Ahmed Aboulnaga                               #
# LOG:           Log file 'test_network_port.log' generated    #
#--------------------------------------------------------------#

#--------------------------------------------------------------#
# Help                                                         |
#--------------------------------------------------------------#
if [ $# -ne 4 ]; then
  echo ""
  echo "Usage: ./test_network_port.sh [target_ip] [target_port] [number_of_loops] [delay_in_secs]"
  echo ""
  echo "Example: ./test_network_port.sh"
  echo "         ./test_network_port.sh 8 1"
  echo "         nohup ./test_network_port.sh 345600 0.5 &"
  echo ""
  exit 0
fi

#--------------------------------------------------------------#
# Check file existence                                         |
#--------------------------------------------------------------#
if ! command -v nc &> /dev/null; then
  echo ""
  echo "ERROR: Command 'nc' does not exist."
  echo ""
fi

#--------------------------------------------------------------#
# Parameters                                                   |
#--------------------------------------------------------------#
V_TARGETIP=${1}
V_TARGETPORT=${2}
V_LOOP=${3}
V_DELAY=${4}

#--------------------------------------------------------------#
# Loop                                                         |
#--------------------------------------------------------------#
i=1
while [ ${i} -le ${V_LOOP} ]; do
  V_TIMESTAMP=`date +'%Y-%m-%d %H:%M:%S.%N'`
  nc -vz ${V_TARGETIP} ${V_TARGETPORT} > test_network_port.tmp 2>&1
  echo "${V_TIMESTAMP}|`cat test_network_port.tmp | tail -1 | awk '{print $9}'`" >> test_network_port.log
  rm -f test_network_port.tmp
  sleep ${V_DELAY}
  i=`expr ${i} + 1`
done

exit 1

Pass the following arguments in this order:

  1. Target IP address
  2. Target port
  3. Number of times to loop
  4. Number of seconds between each loop (fraction of a second is allowed)

Executing it is simple (it should be run from your source server):

root@soadev:/root/temp> ./test_network_port.sh 192.168.1.1 1521 10 1
root@soadev:/root/temp>

It can also be run in the background for 2 days as shown:

root@soadev:/root/temp> ./test_network_port.sh 192.168.1.1 1521 345600 0.5
root@soadev:/root/temp>

It generates a log file called test_network_port.log that has the following output:

2021-12-06 23:01:06.471441274|0.01
2021-12-06 23:01:07.493995977|0.01
2021-12-06 23:01:08.517366674|0.01
2021-12-06 23:01:09.540446846|0.01
2021-12-06 23:01:10.563645494|0.01
2021-12-06 23:01:11.587027598|0.01
2021-12-06 23:01:12.610403491|0.01
2021-12-06 23:01:13.633558440|0.01
2021-12-06 23:01:14.656778628|0.01
2021-12-06 23:01:15.679733290|0.01