Enable ssh and bootstrap WiFi for Raspberry Pi 3 on OSX. Make it executable with "chmod +x enable_ssh_wifi_osx.sh".

enable_ssh_wifi_osx.sh

#!/usr/bin/env bash

ssh_wifi() {
    touch /Volumes/boot/ssh
    
    touch wpa_supplicant.conf
    echo "country=DE" >> wpa_supplicant.conf
    echo "ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev" >> wpa_supplicant.conf
    echo "update_config=1" >> wpa_supplicant.conf
    echo "network={" >> wpa_supplicant.conf
    echo "        ssid=\"$ssid\"" >> wpa_supplicant.conf
    echo "        psk=\"$psk\"" >> wpa_supplicant.conf
    echo "}" >> wpa_supplicant.conf
    mv wpa_supplicant.conf /Volumes/boot/wpa_supplicant.conf

    # eject sd card after setup ssh and wifi
    diskutil list
    read -p "Enter disk identifier to eject the sd card: " disk
    if [ -n $disk ]; then
        sudo diskutil eject /dev/$disk
    else
        echo "Could not eject sd card, so diy."
    fi
}

if [ -d "/Volumes/boot" ]; then
    read -p "Enter SSID: " ssid
    read -p "Enter PSK: " psk
    ssh_wifi "$ssid" "$psk"
else
    echo "Please insert the SD card and run the script again."
fi

helpful!
here is what I've added to mine..

....
.....
    echo "update_config=1"           >> wpa_supplicant.conf
+   echo "ap_scan=1"                 >> wpa_supplicant.conf   
    echo "network={"                 >> wpa_supplicant.conf
+   echo "        scan_ssid=1"       >> wpa_supplicant.conf
    echo "        ssid=\"$ssid\""    >> wpa_supplicant.conf
    echo "        psk=\"$psk\""      >> wpa_supplicant.conf
+   echo "        key_mgmt=WPA2-PSK" >> wpa_supplicant.conf
    echo "}"                         >> wpa_supplicant.conf
.....
....
...
..
.

adds support for hidden SSID,
useful in-case you use your pi as a IP-camera-hub (with ffmpeg or something),
and WPA2-PSK, to match what is the default in many routers now days (default is WPA-PSK).