After many months ... isn’t an ESP8266 shield, either: you can write code for the ESP module, connect the serial pins, and hit the program button. The basic functions of the Arduino IDE ...

These days, connecting your microcontroller ... avrdude -p m328p -c arduino -b 115200 -P net:192.168.1.123:23 -U:yourHexFile.hex. The ESP8266 passes the data straight through its TX and RX lines ...