watch_change

#! /usr/bin/env bash

function cleanup () {
    rm -f /tmp/{cur,last,diffout}.$$
    exit 0
}

trap 'cleanup' SIGINT

sleeptime=1
nochangeiterations=900
timeout=1800

myargs=""
# Pop arguments off of the argument list until we hit one that isn't one of our arguments
while :
do
    if [[ $1 == -h ]]
    then
        echo "Usage: $0 [OPTION]... COMMAND [ARGS]"
        echo "Monitor output from command and show differences when they exist"
        echo "Not that the command cannot currently contain any pipelines"
        echo ""
        echo "    -i<num> Time to pause between checks."
        echo "    -I<num> Number of iterations to wait for no change before exiting.  0 means don't exit."
        echo "    -t<num> Maximum time to watch command.  0 means don't time out."
        exit 0
    fi
    if [[ $1 == -* ]]
    then
        if [ ${#1} -ne 2 ]
        then
            # argument and param stacked together
            myargs="${myargs} ${1}"
            shift
        elif [ ${#1} -lt 2 ]
        then
            break
        else
            myargs="${myargs} ${1} ${2}"
            shift
            shift
        fi
    else
         break
    fi
done

while getopts "i:I:t:" opt ${myargs}
do
    case ${opt} in
      i)
          sleeptime=${OPTARG}
          ;;
      I)
          nochangeiterations=${OPTARG}
          ;;
      t)
          timeout=${OPTARG}
          ;;
    esac
done

lastchange=0
if [ ${timeout} -gt 0 ]
then
    deadline=$(expr $(date +%s) + ${timeout})
fi
while :
do
    "$@" > /tmp/cur.$$
    diff --unified /tmp/last.$$ /tmp/cur.$$ >/tmp/diffout.$$ 2>/dev/null
    if [ $? -ne 0 ]
    then
        lastchange=0
        date
        if [ -s /tmp/diffout.$$ ]
        then
            echo "Differences:"
            cat /tmp/diffout.$$
        else
            echo "Current contents:"
            cat /tmp/cur.$$
        fi
  
        mv /tmp/cur.$$ /tmp/last.$$
    else
        lastchange=$(expr ${lastchange} + 1)
        if [ ${nochangeiterations} -gt 0 ]
        then
            if [ ${lastchange} -gt ${nochangeiterations} ]
            then
                break
            fi
        fi
    fi
    if [ -n "${deadline}" ]
    then
        if [ $(date +%s) -gt ${deadline} ]
        then
            break
        fi
    fi
    sleep ${sleeptime}
done