#!/usr/local/bin/bash 
#

#This script watches a file with du -b (displays the size of the file
#in bytes), perhaps useful if you have a slow internet connection and
#want to track the progress of a large download. Won't stop until you
#press ^C!

# Usage is: watchfile filename [delay_interval]
#
# if delay_interval is not specified, the script pauses 5 seconds
# between each time it shows the file size and elapsed time
# 

#
# This script uses the date command to get the time of day
# so it can print elapsed time. This script does not handle
# rollover to a new day!  
#
# Other stuff of interest:
#    checking for a valid command line parameters
#    (we expect at least 1 and it must be a file).
#

# make sure there is at least 1 command line parameter
if [ $# -lt 1 ]
then
  echo "usage: watchfile filename [delay_interval]"
  exit
fi

# record the file name we are supposed to watch
file=$1

# make sure it is really a file

if [ ! -f $file ]
  then
    echo "Error: $file does not exist or is not a file!"
    exit
fi


# this variable is the time we wait between printing the file size
# (in seconds)

if [ $2 ]
  then 
    # we got 2 parameters, use the second as the delay interval
    delay=$2
  else
    delay=5
fi


# make sure the delay is really a number

# uses expr to find out how many characters in the string $delay
# are not digits (anything greater than 0 means it's not
# an integer so we quit)

if [ `expr $delay : "[^0-9]*"` -gt 0 ]
   then
    echo "invalid delay_interval (must be a number greater than 0)"
    echo "usage: watchfile filename [delay_interval]"
    exit
fi 


# get the initial hour, min and second

ihour=`date +%H`
imin=`date +%M`
isec=`date +%S`

echo "watching the file $1"
echo "Starting time ${ihour}:${imin}:${isec}"

# now go in to a loop that never ends...

while [ 1 ]
  do
    # we sleep for delay seconds, but don't rely on
    # this for printing elapsed time! sleep is not that
    # accurate (we might sleep much longer)

    sleep $delay
    # get the current hour, min and second

    hour=`date +%H`
    min=`date +%M`
    sec=`date +%S`
    
    # compute elapsed time
    dhour=`expr $hour - $ihour`
    dmin=`expr $min - $imin`
    dsec=`expr $sec - $isec`

    elapsed=`expr $dhour "*" 3600 + $dmin "*" 60 + $dsec`
    echo -n "$elapsed seconds: "
    kbytes=`du -L -k $file | cut -f1`
    echo " FILE: " $file " SIZE: " $kbytes "Kbytes"
done