mjhjmtu

Say, I have 'a.txt'. I would like to copy the file and open the newly copied file using VI.

cp a.txt b.txt
vi b.txt

How to combine the two command in a command?

You can use vi itself to do the copy, by opening a.txt then saving the contents to b.txt (effectively copying it) and then switching to b.txt.

Putting it all together:

vi -c 'w b.txt' -c 'e#' a.txt

This is equivalent to running vi a.txt, followed by the :w b.txt command (inside vi), which will save the contents to a file named b.txt. But vi will still be editing a.txt at this point, so you follow up with the :e# command, which means "edit alternative file" (or "edit last file") and given vi has just touched b.txt, it will switch to editing that file.

using && operator

cp a.txt b.txt && vi b.txt

You can write your own function and use that function.
In the below example, you can use cp1 as a command.

example:

$ cat test.txt
function cp1() 
 source_file=$1
 destination_file=$2
 cp "$source_file" "$destination_file"
 vi "$destination"


$ . ./test.txt 
$ cp1 a.txt b.txt 

If you want a way to save you typing you can use bash build in functionality to repeat the last word of the previous command. You can do this by ALT+.

> cp a.txt b.txt
> vi ALT+.

Very useful, and reminds you of the dot operator of vim.

Happy golfing.