3 ways to read files line by line in shell

There are many methods, here are three methods:
Writing method one:

#!/bin/bash
while read line
do
echo $line
done < filename(待读取的文件)

Writing method two:

#!/bin/bash
cat filename(待读取的文件) | while read line
do
echo $line
done

Writing method three:

for line in `cat filename(待读取的文件)`
do
echo $line
done

Explanation:# There is a difference between ##for line-by-line reading and while line-by-line reading, such as:

$ cat file
1111
2222
3333 4444 555

$ cat file | while read line; do echo $line; done
1111
2222
3333 4444 555

$ for line in $(<file); do echo $line; done
1111
2222
3333
4444
555

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