tails a (runit) service by name, or tail all services on a machine

svtail.sh

# tail a service by name
#
#   svtail cad-server 50 
#
# becomes
#
#   tail -fn 50 /var/log/cad-server/current
#
svtail() {
  local n=${2:-50}
  local sv=${1}

  if [[ -z $sv ]]; then
    echo "Tailing all"
    # find services with logs in standard place (our runit setup)
    local services=$(__intersect <( printf "%s\n" `ls /etc/sv` ) <( printf "%s\n" `ls /var/log` ))
    tail -fn $n `printf "/var/log/%s/current " $services`
  fi

  if [[ ! -e /etc/sv/$sv ]]; then
    echo "Could not find service $sv in /etc/sv"
    return 1
  fi
  tail -fn $n /var/log/$sv/current 
}

__intersect() {
  # -1, suppress only in 1, -2 supress only in 2 (leaving -3 - only in both)
  comm -12 $1 $2
}