#!/usr/bin/ksh

# INSTALLATION:
# Copy this script as /opt/bin/nohup.sh and give execute rights
#
# See article at
#    http://www.sun.com/bigadmin/content/submitted/save_with_nohup.jsp
#
# CONFIGURATION:
# Script is started with the interpreter specified in $NOHUP_SHELL
# variable. If variable is not set, the default interpreter is started
# according to the script file's name extension:
#   - *.sh started with /usr/bin/ksh
#   - *.pl started with /usr/bin/perl
#   - *.rb started with /usr/bin/ruby
#   - *.py started with /usr/bin/python
# output is logged into the /var/tmp directory; export the
#   NOHUP_LOGDIR variable to change the directory
# set NOHUP_MONITORING=yes to monitor the command output with 'tail -f'
#   just after starting the script in the background, you can stop this
#   monitoring process without stopping the nohup command 
#
# USAGE:
# There are 2 different ways:
#   1. starting from command line
#        nohup.sh <command> <args...>
#   2. put into a script as the first line
#        #!/usr/bin/ksh /opt/bin/nohup.sh
#      nohup.sh starts automatically by calling the script and
#      executes the original script in the background
#
# Both ways have the same functionality: 
#   - the corresponding interpreter is started according to the file
#     extension or the $NOHUP_SHELL variable
#   - output is logged into $NOHUP_LOGDIR or if it is not specified
#     into the /var/tmp
#   - log file is the command or script name postfixed with date
#       e.g: mynohupscript_2007_03_23_11_11_22.log
#
# Example:
#   uncomment, save following lines and execute to see how it works
# #!/usr/bin/ksh /opt/bin/nohup.sh
# 
# default_cycles=3  
# default_sleeping=1
# cycles=${1:-$default_cycles}
# sleeping=${2:-$default_sleeping}
# i=0
# while [[ $i -lt $cycles ]]
# do
#   echo "$(date): $i"
#   sleep $sleeping
#   i=$((i+1))
# done


signal_handler() {
  kill $TAIL_PID
  echo "
--- $LOGFILE monitoring has stopped ---
--- background process is running yet, pid: $PID"
  ps -fp $PID | tail -1
  exit 0
}

filename=`basename $1`

if [[ -z $NOHUP_SHELL ]] ;then
  # starting the interpreter according to its extension, .pl perl, .rb ruby ...
  extension=${filename##*.}
  case $extension in
    pl) NOHUP_SHELL=/usr/bin/perl ;;
    rb) NOHUP_SHELL=/usr/bin/ruby ;;
    py) NOHUP_SHELL=/usr/bin/python ;;
    *|sh) NOHUP_SHELL=/usr/bin/ksh ;;
  esac
fi

# configuration setting, default values
: ${NOHUP_LOGDIR:=/var/tmp}
: ${NOHUP_MONITORING:=}

filename=${filename%.*}
LOGFILE=$NOHUP_LOGDIR/${filename}_`date +%Y_%m_%d_%H_%M_%S`".log"

echo "start command : $NOHUP_SHELL $@"
nohup $NOHUP_SHELL $@ >>$LOGFILE 2>&1 &
PID=$!

echo "pid           : $PID"
echo "check log file: $LOGFILE"

# optional tailing the output
if [[ -n $NOHUP_MONITORING ]] ;then
  trap signal_handler INT TERM 
  echo "
$LOGFILE is reported here with tail -f
Stop it with CTRL-C.
CTRL-C doesn't mean stopping the background process.

--- monitoring $LOGFILE ---
"
  # touching the log file to ensure having file when starting the tail
  touch $LOGFILE
  tail -f $LOGFILE &
  TAIL_PID=$!
  wait $PID
  kill $TAIL_PID
  echo "
--- background process has finished ---
exiting...
"
fi

##############################################################################
### This script is submitted to BigAdmin by a user of the BigAdmin community.
### Sun Microsystems, Inc. is not responsible for the
### contents or the code enclosed. 
###
###
### Copyright 2008 Sun Microsystems, Inc. ALL RIGHTS RESERVED
### Use of this software is authorized pursuant to the
### terms of the license found at
### http://www.sun.com/bigadmin/common/berkeley_license.html
##############################################################################