Answer by sumitsinghdeode for What are file descriptors, explained in simple terms?

Addition to above all simplified responses.
If you are working with files in bash script, it's better to use file descriptor.
For example:-
You want to read and write from/to the file "test.txt".
Use the file descriptor as show below

FILE=$1 # give the name of file in the command line
exec 5<>$FILE # '5' here act as the file descriptor
# Reading from the file line by line using file descriptor
while read LINE; do
    echo "$LINE"
done <&5

# Writing to the file using descriptor
echo "Adding the date: `date`" >&5 
exec 5<&- # Closing a file descriptor