Notepad++

Problem:

Add a text at the start of every line

Solution:

Press Ctrl+H keys
In search and replace box
search for ^ and in replace text box type the text that you want to display.

Problem:

Add a text at the end of every line

Solution:

Press Ctrl+H keys
In search and replace box
search for $ and in replace text box type the text that you want to display.

Problem:

I need to combine two separate files line by line.

For Eg:
Consider I have two text files file 1 and file 2.
File 1 contains the following text

Start of Line 1
Start of Line 2
Start of Line 3
.
.
.
Start of Line N

File 2 Contains the following text

End of Line 1
End of Line 2
End of Line 3
.
.
.
End of Line N

Solution:

1. Open a new tab ( Ctrl + N )
2. Select the contents of File 1 and paste them in this new tab
3. Write any symbols in a new line. Eg: ______ ( Type 3 _ characters )
4. Select the contents of File 2 and paste them, in the new tab, BELOW the ___ line
5. Open the Replace dialog ( Ctrl + H )
6. SEARCH : (?s)^___.+|(?-s)^.*(?=\R(?:.*\R){n}(^.*)) ( Just replace n with the appropriate number of lines )
7. REPLACE: ?1$0\1
8. OPTIONS: Wrap Around and Regular expression set. All other options unticked
9. ACTION: Click on the Replace All button

Result:

File 3

Start of Line 1End of Line 1
Start of Line 2End of Line 2
Start of Line 3End of Line 3
..
..
..
Start of Line NEnd of Line N