Bash while read line

The following syntax is used for bash shell to read a file using while loop:

1. while read -r line; do. echo "$line" ; done < input.file.
2. while IFS= read -r line; do. echo $line; done < input.file.
3. $ while read line; do. echo $line; done < OS.txt.
4. #!/bin/bash. filename='OS.txt' n=1. ...
5. #!/bin/bash. filename=$1. while read line; do.