epoch formatting, shell function (mac os / BSD)

epoch.sh

# epoch format, use with arg or pipe; no argument -> echo current epoch
function epoch() { 
  fmt="+%Y-%m-%dT%H:%M:%S%z"
  if [ -t 0 ] && [ -z "$1" ]; then
    # no input, echo current epoch
    date "+%s"
  elif [[ -z "$1" ]]; then
    # no arg, use piped value
    xargs -I {} sh -c "date -r {} $fmt"
  else
    date -r $1 $fmt 
  fi
}