Midnight Commander has a built in editor which is started by F4 function key when over the desired file in the browse mode. It can also be invoked in standalone mode by executing
mcedit <filename>
Here is a list of actions which can be triggered in the edit mode.
F1 Displays help
F2 Saves current file
F3 Marks the start of the text selection. Move cursor any direction to select. Second hit marks the end of the selection.
F4 Brings up the text search/replace dialog
F5 Copies selected text to the cursor location (copy/paste)
F6 Moves selected text to the cursor location (cut/paste)
F7 Brings up the text search dialog
F8 Deletes selected text
F9 Focuses to the main menu on the top of the screen
F10 Exits the editor