TITLE: Shell script to get wifi password in macOS
DATE: 2019-11-05
AUTHOR: John L. Godlee
====================================================================


macOS uses the BSD security command to access information from the 
system keychain. With this command you can access all the same 
information which is normally stored in Keychain Access.app and 
more. I wrote a script which prints the WiFi password for either 
the current network, or a specified network to the terminal. This 
was mostly an exercise for me to learn how getopts works.

The script is below:

    #!/bin/bash

    
ssid=$(/System/Library/PrivateFrameworks/Apple80211.framework/Versio
ns/Current/Resources/airport -I | grep " SSID:" | awk -F': ' 
'{print $2}')

    while getopts ":n:" opt; do
        case $opt in 
            n)
                # If flag is given with argument
                ssid="$OPTARG"
                ;;
            \?)
                # If incorrect flag given
                echo "-$OPTARG is not a valid option" >&2
                exit 1
                ;;
            :)
                # If flag is given without argument
                echo "-$OPTARG requires an argument" >&2
                exit 1
                ;;
        esac
    done

    security find-generic-password -wga "$ssid"

If I run ./wifi.sh -n SSID the script will look for a network with 
the SSID SSID then return its password. If I run ./wifi.sh -n I 
will get the response: -n requires an argument. If I run ./wifi.sh 
-a I will get the response: -a is not a valid option. If I run 
./wifi.sh I will get the password for the WiFi network I am 
currently attached to.