Unix basic shell script help needed please?

Question

I need some help writing a basic Unix shell script that will run on AIX:

Loop that will run a netstat command (netstat -an| grep 16752| grep ESTABLISHED| wc -l) that counts sessions every second and also gets the timestamp and redirects that data to a log for review. I would like to be able to input in minutes how long it should run for if possible. I would like the output to be pretty basic and look like similar to this:

timestamp  #count
timestamp  #count

Answer 1

Here is a hint.

date +%s

returns the number of seconds since the epoch. Since there are 60 seconds in a minute so you can easily do the math. Both ksh and bash allow you to do arithmetic with double parentheses around an expression like this

echo $(( 324567 / 60 ))

Answer 2

I tested this under ksh, which I believe is the shell used in AIX. Unlike my comment to the question, it seems "until" works OK. This script assumes bc is working; I'm not sure if the $( ) syntax works in your likely old shell, but it's a gamble and without specific / shell version information, it will have to do.

Usage: thisscript.sh *minutes* Calls the script with a number of minutes. It will run the commands every second until it has counted down from the calculated loop_total to zero.

There's no visible output other than a couple "start / end" and duration messages. Everything is piped to the LOG_FILE. If you want output to the screen, you'll likely have to use variables to store the data and THEN output that to the LOG_FILE. Cheers.

#!/bin/sh
LOG_FILE="connections.txt"
PORT="16752"
COMMAND="netstat -an | grep ${PORT} | grep ESTABLISHED | wc -l"
TIMESTAMPER="date +'%D %H:%M:%S'" # Format like "mm/dd/yy hh:mm:ss"


if test -z "$1" ; then
  echo "ERROR: No duration provided"
  exit 1
else 
  INPUT="$1" # Store the number of minutes wanted
  LOOP_TOTAL=$(( ${INPUT} * 60 ))
  echo "Started on $( eval ${TIMESTAMPER} )"
  echo "Executing for: ${LOOP_TOTAL} seconds (${INPUT} minutes)" 
  COUNTDOWN=${LOOP_TOTAL} # Initialize counter

  until test ${COUNTDOWN} -eq 0 ; do
    COUNTDOWN=$(echo "${COUNTDOWN} - 1" | bc)
    OUTPUT=$( eval ${COMMAND} )
    if test -z "${OUTPUT}"; then
      OUTPUT="0" # greps are blank when no connection, so fill out as 0
    fi  

    TIMESTAMP=$( eval ${TIMESTAMPER} )  
    echo "${TIMESTAMP} #${OUTPUT}"
    sleep 1;
  done >> ${LOG_FILE}

  echo "Finished on $( eval ${TIMESTAMPER} ) "
fi