#! /bin/bash

# A useful shell script to calculate the number of bytes
# used by all files in the given directory that end with a particular extension
FILES=`ls *.${1}`  # get the list of files
TOT=0
for FILE in $FILES
do
  DET=`ls -l $FILE`  # for a particlar file, get its details
  CNT=0
  for DETP in $DET  # cycle through file details until get to size
  do
     #echo "$CNT $DETP"
     if [ $CNT -eq 4 ]
     then
        TOT=$(( $TOT + $DETP ))
        #echo $DETP
     fi
     ((CNT++))
  done
done
echo $TOT