Vi IMproved, a programmer's text editor, providing several modes for different kinds of text manipulation. Pressing "i" enters edit mode. "Esc" goes back to normal mode, which doesn't allow regular text insertion.

# To open a file:
vim file

# To enter text editing mode (insert mode):

# To copy ("yank") or cut ("delete") the current line (paste it with 'P'):

# To undo the last operation:

# To search for a pattern in the file (press 'n'/'N' to go to next/previous match):

# To perform a regex substitution in the whole file:

# To save (write) the file, and quit:

# To quit without saving: