Shell逐行读取文件的4种方法

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

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

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

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

#!/bin/bash
FILENAME="$1"
TIMEFILE="/tmp/loopfile.out" > $TIMEFILE
SCRIPT=$(basename $0)
function usage(){
echo -e "\nUSAGE: $SCRIPT file \n"
exit 1
}
function while_read_bottm(){
while read LINE
do
echo $LINE
done < $FILENAME
}
function while_read_line(){
cat $FILENAME | while read LINE
do
echo $LINE
done
}
function while_read_line_fd(){
exec 3<&0
exec 0< $FILENAME
while read LINE
do
echo $LINE
done
exec 0<&3
}
function for_in_file(){
for i in  `cat $FILENAME`
do
echo $i
done
}
if [ $# -lt 1 ] ; then
usage
fi
echo -e " \n starting file processing of each method\n"
echo -e "method 1:"
echo -e "function while_read_bottm"
time while_read_bottm >> $TIMEFILE
echo -e "\n"
echo -e "method 2:"
echo -e "function while_read_line "
time while_read_line >> $TIMEFILE
echo -e "\n"
echo -e "method 3:"
echo "function while_read_line_fd"
time while_read_line_fd >>$TIMEFILE
echo -e "\n"
echo -e "method 4:"
echo -e "function  for_in_file"
time  for_in_file >> $TIMEFILE

method 1:
function while_read_bottm
real    0m5.689s
user    0m3.399s
sys    0m1.588s
method 2:
function while_read_line
real    0m11.612s
user    0m4.031s
sys    0m4.956s
method 3:
function while_read_line_fd
real    0m5.853s
user    0m3.536s
sys    0m1.469s
method 4:
function  for_in_file
real    0m5.153s
user    0m3.335s
sys    0m1.593s

real    0m5.153s    method 4 （for 循环法）
real    0m5.689s    method 1  （while 釜底抽薪法）
real    0m5.853s    method 3    （标识符法）
real    0m11.612s  method 2    （管道法）

while read LINE
do
echo $LINE
done < $FILENAME