Decode output from a variety of hex dumps, such as BSD hexdump and Java javax.net.debug=all.

hexparse.js

#! /usr/bin/env node

// decode output from a variety of hex dumps, such as
// - BSD hexdump / hd
//   00000000  50 4f 53 54 50 4f 53 54  50 4f 53 54 50 4f 53 54  |POSTPOSTPOSTPOST|
// - od -t x1
//   0000000    50  4f  53  54  50  4f  53  54  50  4f  53  54  50  4f  53  54
// - Java javax.net.debug=all
//   0000: 50 4F 53 54 50 4F 53 54   50 4F 53 54 50 4F 53 54  POSTPOSTPOSTPOST

var readline = require('readline'),
    rl = readline.createInterface({
        input:  process.stdin,
        output: null
    }),
    re = /^[0-9A-F]{4,}:?((?: +[0-9A-F]{2}){1,16})( |$)/i,
    spaces = / +/g;

rl.on('line', function (s) {
    var m = re.exec(s);
    if (m === null)
        return;
    process.stdout.write(Buffer.from(m[1].replace(spaces, ''), 'hex'));
});