Bash functions to convert to and from milliseconds since epoch UTC. Requires moment (http://momentjs.com/docs/) to be installed.

bash-milliseconds-functions

function millis {
  nvm use v0.10.12 > /dev/null && node -e "var m = require('moment'); console.log(+m.utc('${1}', ['MM/DD/YY', 'YYYYMMDDTHH:mm:ss']))"
}

function fmillis {
  nvm use v0.10.12 > /dev/null && node -e "var m = require('moment'); console.log(m(${1}).utc().format())"
}

Same functions in a source file. This won't work on OSX though, only linux. BSD bash has the somewhat-similar-but-different -f and -r flags though.

#!/bin/bash

function millis(){
  date --date="${1}" +%s -u
}

function fmillis(){
  date -d @${1} +"%Y%m%dT%H:%M:%S" -u
}