(1)
# Use existing vnet and subnet.
$rg="fy"
az group create -g $rg -l eastus
az network vnet create -g $rg -n vnet --address-prefix 10.0.0.0/16
az network vnet subnet create -g $rg --vnet-name vnet -n subnet1 --address-prefixes 10.0.0.0/24
az network vnet subnet create -g $rg --vnet-name vnet -n subnet2 --address-prefixes 10.0.1.0/24
az vm create -g $rg -n vma --count 5 --image ubuntults --nsg-rule None --vnet-name vnet --subnet subnet1
az vm create -g $rg -n vmb --count 5 --image ubuntults --nsg-rule None --vnet-name vnet --subnet subnet2

(2)
# Use existing vnet and subnet in another resource group
$rg1="fy2"
$rg2="fy3"
az group create -g $rg1 -l eastus
az group create -g $rg2 -l eastus
az network vnet create -g $rg1 -n vnet --address-prefix 10.0.0.0/16 --subnet-name subnet --subnet-prefix 10.0.0.0/24
$subnetId=$(az network vnet subnet show -g $rg1 -n subnet --vnet-name vnet --query [id] -o tsv)
az vm create -g $rg2 -n vm --count 5 --image ubuntults --nsg-rule None --subnet $subnetID

(3)
# Specify address prefix
$rg="fy4"
$count="150"
az group create -g $rg -l eastus
# Will create new vnet and subnet
az vm create -g $rg -n vma --count $count --image ubuntults --nsg-rule None --vnet-address-prefix 10.0.0.0/8 --subnet-address-prefix 10.0.0.0/16
# Will use vnet and subnet created just now
az vm create -g $rg -n vmb --count $count --image ubuntults --nsg-rule None
az vm create -g $rg -n vmc --count $count --image ubuntults --nsg-rule None