Uly.me

cloud engineer

Check Open Ports Remotely

Here are a few tools to check if ports are open from a remote host.

nc -zvw10 192.168.0.1 22
nmap 192.168.0.1 -p 22
telnet 192.168.0.1 22

You may have to install netcat and nmap if missing in your distro.

yum install nc
yum install nmap

Terraform GCloud VM Image Family

How to implement image family with Terraform in GCP.

Declare the machine image in terraform.tfvars.

image-family = "centos-7"

Declare data type for the machine image in maint.tf.

data "google_compute_image" "my_image" {
  family  = var.image-family
  project = "your-project-id"
}

In main.tf use “google_compute_instance” under boot disk section in main.tf.

boot_disk {
  initialize_params {
    image = data.google_compute_image.my_image.self_link
  }
}

Bash Variable Empty

Here’s how to check in Bash if a variable is empty or unset.

if [ -z "${VAR}" ]; 
then
  echo 'do something'
else
  echo 'do another'
fi

One liner

if [ -z "${VAR}" ]; then echo 'do something'; else echo 'do another'; fi

The inverse

if [ ! -z "${VAR}" ]; 
then
  echo 'do something'
else
  echo 'do another'
fi
if [ ! -z "${VAR}" ]; then echo 'do something'; else echo 'do another'; fi