4. A method to read the file line by line Shell

Method 1: highest efficiency, the most common method of execution while loop.

function while_read_LINE_bottm(){
While read LINE
do
echo $LINE
done  < $FILENAME
}

Method 2: Redirect method; Pipeline Act: cat $ FILENAME | while read LINE

Function While_read_LINE(){
cat $FILENAME | while read LINE
do
echo $LINE
done
}

Method 3: Method Wenjianmiaoshufu

Function while_read_line_fd(){
Exec 3<&0
Exec 0<$FILENAME
While read LINE
Do
Echo $LINE
Exec 0<&<3
}

Method 4 for loop

function  for_in_file(){
For  i  in  `cat $FILENAME`
do
echo $i
done
}