bulk write in Unix using shell script - shell

Question

Is there any way to write bulk data in a file in shell script instead of writing line by line code in file?
In below script, I want to write difference between arrival time and generation time of files in test.csv file.
########################################################
echo "Starting the Execution for Time difference\n";
############################################################
# Functions used across the script
datediff() {
Unixtime=`echo $1 $2 $3 $4`
Filetime=`echo $5 $6 $7 $8`
echo $Unixtime;
echo $Filetime;
d1=`date -d "$Unixtime" +%s`
d2=`date -d "$Filetime" +%s`
echo $d1;
echo $d2;
TIME_DIFF=`expr $d1 - $d2`
TIME_DIFF=`expr $TIME_DIFF / 60`
echo $TIME_DIFF;
echo "$Unixtime,$Filetime,$TIME_DIFF,$9" >> ../test.csv
}
rm -f ../test.csv;
for i in `ls -1 | grep -v 'DelayCheck.s*'`
do
DayMonth=`ls -lrt $i | awk '{print $7" "$6" "}'`
Year=`ls --full-time $i | awk '{print $6}' | cut -c1-4`
HourMin=`ls -lrt $i | awk '{print " "$8}'`
timeA=`echo $DayMonth $Year $HourMin`
FileYearMonDay=`ls -ltr $i | awk '{print $9}' | awk -F'--' '{print $3}' | cut
-c2-9`
timeB1=`date -d $FileYearMonDay +'%d %b %Y'`
timeB2=`echo $i | awk -F'--' '{print substr($3,10,13)}' | sed -e
's/../:&/2g'`
timeB=`echo $timeB1 $timeB2`
echo "Time A is $timeA";
echo " Time b is $timeB";
datediff $timeA $timeB $i
done
echo $?;
script is working fine, but the problem is there is over 100k files. So script performance is bad.
I had tried to search is there any way to write bulk data in a file but I didn't find any solution.