GNU nano

Help読み。

Main nano help text

The nano editor is designed to emulate the functionality and
ease-of-use of the UW Pico text editor. There are four main
sections of the editor. The top line shows the program version,
the current filename being edited, and whether or not the file has
been modified. Next is the main editor window showing the file
being edited. The status line is the third line from the bottom
and shows important messages. The bottom two lines show the most
commonly used shortcuts in the editor.

The notation for shortcuts is as follows: Control-key sequences
are notated with a caret (^) symbol and can be entered either by
using the Control (Ctrl) key or pressing the Escape (Esc) key
twice. Escape-key sequences are notated with the Meta (M-) symbol
and can be entered using either the Esc, Alt, or Meta key
depending on your keyboard setup. Also, pressing Esc twice and
then typing a three-digit decimal number from 000 to 255 will
enter the character with the corresponding value. The following
keystrokes are available in the main editor window. Alternative
keys are shown in parentheses: