<oerjan> learn `edit <file> gives you a url, then in your browser: (1) Press Fetch (2) Make your changes (3) Press edit (4) Paste the command line at the top into the channel.

#!/bin/bash
declare {{a..h},{j..t}}="$((i++))" letters=({{a..h},{j..t}}); while read -r; do echo "${letters[18-${REPLY:0:1}]}$((20-${REPLY:1}))"; done