add environment variable mac code example

Example 1: print env variable mac

# Print all environment variables 
printenv

Example 2: mac addres enviroment variable windos

wmic path Win32_NetworkAdapter where "PNPDeviceID like '%PCI%' AND AdapterTypeID='0'" get name, MacAddress

Example 3: mac set environment variable

HIMANSHUs-MacBook-Pro:~ himanshu$ export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home