Using Linux bash

1. Write a command sequence to print the login names of all users on a system?

2. What is the difference between $$ and $!?

3. I want to read all input to the command from file1 direct all output to file2 and error to file 3, how can I achieve this?

4. Given a file find the count of lines containing word EFG.

5. How to list files where third letter is a or b ?

6. How to remove array element with id 4 ?

7. Write a shell script that adds an extension .Newto all the files in a directory.

8: How will you insert a line ABCDEF at every 50th line of a file?

9. Write a command sequence to find all the files modified in less than 5 days and print the record count of each.

10. What is the difference between $* and $@?

11. Given a file, replace all occurrence of word ABC with DEF from 5th line till end in only those lines that contains word MNO