$ls -l
-rw-r--r--   1 userid   staff           166 Mar 01 04:21 f1
-rw-r--r--   1 userid   staff           166 Mar 01 04:21 f2
-rw-r--r--   1 userid   staff           166 Mar 01 04:21 f3
-rw-r--r--   1 userid   staff           166 Mar 01 04:21 f4
-rw-r--r--   1 userid   staff           166 Mar 01 04:21 f5
-rw-r--r--   1 userid   staff           166 Mar 01 04:22 f6
-rw-r--r--   1 userid   staff           166 Mar 01 04:22 f7
-rw-r--r--   1 userid   staff           166 Mar 01 04:22 f8
-rw-r--r--   1 userid   staff           166 Mar 01 04:22 f9
-rwxr-xr-x   1 userid   staff          2514 Mar 01 05:21 seperate.sh

Script seperate.sh

# Deleting previously created files by this script is any.......
rm -r dir1 dir2 dir3 list* size* thread* >/dev/null 2>/dev/null
# Preparing a file containing all the file names and their corrosponding sizes in the current directory
ls -l |grep -v "dr--*"|grep -v "total"|grep -v $0|awk '{print $9" :" $5}' >sizelist
 

                        ##################### PART1 #########################
# Calculating the total files size in current directory and taking 1/3 of it as reference for getting files for thread 1,2,3
totsize=0
for i in `cat sizelist|awk -F: '{print $2}'`
do
((totsize=$totsize+$i))
done
((refsize=$totsize/3))
 

                        ##################### PAR2 #########################
# Preparing a list of thread1 files
filelist1=" "
thread1size=0
for i in `cat sizelist|awk -F: '{print $1}'`
do
filesize=`cat sizelist|grep "$i"|awk -F: '{print $2}'`
((thread1size=$thread1size+$filesize))
if [ $thread1size -lt $refsize ]
then
filelist1=$filelist1:$i
else
filelist1=$filelist1:$i
break
fi
done
echo $filelist1 |tr -s : " " >thread1
 
                       ##################### PART3 ##########################
# Preparing a file containing  list of filenames excluding the thread1 files for getting thread2 files
cat sizelist >list2
for i in `cat thread1`
do
cat list2|grep -v $i >list2
done
# Preparing a list of thread2 files
filelist2=" "
threadr2size=0
for i in `cat list2|awk -F: '{print $1}'`
do
filesize=`cat list2|grep "$i"|awk -F: '{print $2}'`
((thread2size=$thread2size+$filesize))
if [ $thread2size -lt $refsize ]
then
filelist2=$filelist2:$i
else
filelist2=$filelist2:$i
break
fi
done
echo $filelist2 |tr -s : " " >thread2
 
                       ##################### PART4 #############################
# Preparing list of remaining files for thread3
#echo $thread2
cat list2 >thread3
for i in `cat thread2`
do
cat thread3|grep -v $i|awk -F: '{print $1}'>thread3
done
 
                       ##################### PART5 #############################
#creating three directories and coping thread1 and thread2 and thread3 files to them
mkdir dir1 dir2 dir3
for i in `cat thread1`
do
cp $i dir1/
done
for i in `cat thread2`
do
cp $i dir2/
done
for i in `cat thread3`
do
cp $i dir3/
done
echo "Total size of all files in the current directory is $totsize"
echo "The reference size is 1/3 is $refsize"
echo "Thread one files are: `cat thread1`"
echo "Thread two files are: `cat thread2`"
echo "Thread three files are: `cat thread3`"

$ seperate.sh

Total size of all files in the current directory is 1494
The reference size is 1/3 is 498
Thread one files are:  f1 f2 f3
Thread two files are:  f4 f5 f6
Thread three files are: f7
f8
f9