Text editor

A text editor is a program to create and edit of text files. Although not it is not impossible to edit files without using one, text editors make it easy to edit configuration files.

Software
More text editor options can be found online in the app-editors category or by running:

Vim and Vi
If Vim is installed the vi and vim commands become synonymous due to the following link:

The synonymous use also holds for setting editor defaults.

Sudo editor
sudo does not preserve the user's environment variables and therefore may have a different default editor.

Visudo editor
Due to the sensitive nature of it may only edited via the visudo command which in turn is limited to a predefined selection of editors. Type man visudo for more information.

Setting system default
The system wide default text editor can be defined in the file. To change the Gentoo system default from nano to Vim add the path to Vim's executable:

The system default editor can also be set with the eselect utility. Replace  in the following command with a number corresponding to the text editor of choice:

Actually eselect modifies the file above. It seems that the old method of editing doesn't work any more.