#!/bin/bash

stdin_logger() {

  local log_file="$1"
  local lock_file="$log_file.lock"
  local LOG_FD
  local line
  local logbuffer=()
  local counter=0
  local buffer_size=1000 

  trap "stdin_logger_flush $log_file $lock_file" EXIT INT HUP TERM
  
  while IFS= read -r line ; do
    logbuffer+=("$line")
    ((counter++))

    if [ $counter -ge $buffer_size ] ; then
      stdin_logger_flush "$log_file" "$lock_file"
    fi

  done
  stdin_logger_flush "$log_file" "$lock_file"
}

stdin_logger_flush() {
 
 local log_file="$1"
 local lock_file="$2"

 [ -z "$counter" ] && return
 
 # $logfile bei Bedarf oeffnen
 [ -n "$LOG_FD" ] || exec {LOG_FD}<>$lock_file

 dbg "logbuffer flush, logbuffer_count: ${#logbuffer} counter: ${counter}"  
 local i
 if flock --exclusive --timeout 10 $LOG_FD ;then
         for((i=0;i<$counter;i++));do
                 dbg "writing line >${logbuffer[$i]}< ..." 
                 echo "${logbuffer[$i]}" >>$log_file
         done
         logbuffer=()
         counter=0
         flock --unlock $LOG_FD
 fi
}

dbg() {
        # Debug ausgabe am Bildschirm
        if [ "$DEBUG" == "1" ] ;then
                echo "DEBUG: $*" >&2
        fi
}

machwas() {
        local i=0
        for((x=1;x<=10;x++)) ; do
                for name in anton peter "" susanne fritz mira markus tina ;do
                        echo "$name"
                done
        done

        }

# --- Hauptprogramm ---

declare -x DEBUG=1

# - mehrere logger definieren -
#
logger_data()  { stdin_logger data.log  ; }
logger_extra() { stdin_logger extra.log ; }

machwas | logger_data
machwas | logger_extra