How do I paste the name of the alternate (previously edited) file into the buffer?

Explanation

The # register holds the name of the alternate file — the file you were editing just before the current one. Using "#p in normal mode pastes this filename directly into the buffer, which is handy for constructing commands, inserting file references, or quickly noting paths.

How it works

• "# specifies the # (alternate file) register
• p pastes the register contents after the cursor
• The alternate file is the one you most recently switched away from — the same target as <C-^> or :e #
• In insert mode, you can use <C-r># to insert the same value while typing

Example

You're editing main.go and previously edited config.go. The alternate file is config.go.

"#p

Inserts config.go at the cursor position in normal mode.

In insert mode:

<C-r>#

Inserts config.go inline while typing.

Tips

• The % register holds the current filename; # holds the alternate filename
• Use "#P to paste before the cursor instead of after
• The alternate file changes each time you switch files with <C-^>, :e #, :bn, etc.
• Combine with :vs <C-r>#<CR> to open the alternate file in a vertical split from the command line