3 ways the shell reads files by row _linux Shell

There are a lot of ways, and here are three ways to write:
Writing a:

Copy Code code as follows:

#!/bin/bash
While Read line
Todo
Echo $line
Done < filename (files to be read)

Writing two:

Copy Code code as follows:

#!/bin/bash
Cat filename (Files to be read) | While Read line
Todo
Echo $line
Done

Writing three:

Copy Code code as follows:

For line in ' cat filename (file to be read) '
Todo
Echo $line
Done

Description
For row-by-line reading and while-line-by-row reading are different, such as:

Copy Code code as follows:

$ 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