BBEdit Text Filter to transform unix timestamp to human a readable string in the UTC time zone.

unix-timestamp-converter.js

#!/usr/local/bin/node

// Note that a more standard node hashbang doesn't seem to work
// in a BBEdit Text Filter (or perhaps it's Homebrew installed node weirdness).
// So, change the hashbang to a path to your node executable

process.stdin.resume();
process.stdin.setEncoding('utf8');

process.stdin.on('data', function (data) {
    process.stdout.write((new Date(data * 1000)).toUTCString());
});