Bash manage child processes

gistfile1.txt

#!/usr/bin/env bash

cleanup() {
  flock unlock
  exit
}

die() {
  echo "$*"
  exit
}

kill() {
  [[ -z "$1" ]] && return 1
  [[ $1 -gt 0 ]] && builtin kill $1 >/dev/null 2>&1 && echo "killed $1" 1>&2
}

poke() {
  [[ -z "$1" ]] && return 1
  builtin kill -0 $1 >/dev/null 2>&1
}

sleep() {
  local IFS
  [[ -n "${_snore_fd:-}" ]] || exec {_snore_fd}<> <(:)
  read ${1:+-t "$1"} -u $_snore_fd || :
}

tail1() {
  if [[ ${tail1pid:-0} -eq 0 ]] || ! poke $tail1pid; then
    [[ $(((last_tail1=$(date +%s))-${last_tail1:-0})) -le 1 ]] && die "restarting tail1 too fast"
    tail -n 0 -f --pid=$$ ${logfile:-/var/log/messages} >/dev/null &
    tail1pid=$!
    echo "Started $tail1pid: tail1 -n 0 -f --pid=$$"
  else
    [[ -z "$last_tail1" ]] && echo "Already started $tail1pid"
    last_tail1=0
  fi
}

tail2() {
  if [[ ${tail2pid:-0} -eq 0 ]] || ! poke $tail2pid; then
    [[ $(((last_tail2=$(date +%s))-${last_tail2:-0})) -le 1 ]] && die "restarting tail2 too fast"
    tailfile -n 0 -f --pid=$$ ${logfile:-/var/log/messages} >/dev/null &
    tail2pid=$!
    echo "Started $tail2pid: tail2 -n 0 -f --pid=$$"
  else
    [[ -z "$last_tail2" ]] && echo "Already started $tail2pid"
    last_tail2=0
  fi
}

tail3() {
  if [[ ${tail3pid:-0} -eq 0 ]] || ! poke $tail3pid; then
    [[ $(((last_tail3=$(date +%s))-${last_tail3:-0})) -le 1 ]] && die "restarting tail3 too fast"
    tailfile -n 0 -f --pid=$$ ${logfile:-/var/log/messages} >/dev/null &
    tail3pid=$!
    echo "Started $tail3pid: tail3 -n 0 -f --pid=$$"
  else
    [[ -z "$last_tail3" ]] && echo "Already started $tail3pid"
    last_tail3=0
  fi
}

_tail() {
  [[ "$*" =~ --pid=([0-9]+) ]]
  local ppid=${BASH_REMATCH[1]}
  echo "${0##*/} tailing $logfile" 1>&2	
  while poke $ppid; do
    [[ -n "$P" ]] && echo -n "$P" 1>&2
    sleep .1
  done
}

flock() {
  local tmp=${TMP:-/tmp}
  local lockfile=$tmp/.${0##*/}
  case "$1" in
    lock)
      trap - 0
      [[ -z "$last_restart" && -f $lockfile ]] && die "$lockfile locked" || touch $lockfile
      trap cleanup 0
      ;;
    unlock)
      rm -fv $lockfile
      ;;
  esac

  trap cleanup 0 2 3 15
}

main() {
  while :; do
    tail1
    tail2
    tail3
    if [[ -z "$TERM" ]]; then
      sleep .1
    else
      read -s -t .1 -n1 -p "$p" key
      case "$key" in
        1) kill $tail1pid;;
        2) kill $tail2pid;;
        3) kill $tail3pid;;
        p) echo "-- -1 $tail1pid -2 $tail2pid -3 $tail3pid"; ps $tail1pid $tail2pid $tail3pid; pstree -acp $$;;
        q) break;;
      esac
    fi
  done
}

echo "Starting $0 $@ ($$)"

case "${0##*/}" in
  tailfile) _tail "$@"; exit;;
esac

# Process non-hidden args normally
while getopts 'a:b:c:' o; do
  case "$o" in
    *) true;;
  esac
done
shift $(($OPTIND-1))
logfile=$1; shift
export logfile

# And now business as usual...

main