Vi IMproved, a programmer's text editor, providing several modes for different kinds of text manipulation. Pressing i enters edit mode; the normal mode (accessed via ) doesn't allow regular text editing.

# To open a file:
vim file

# To enter text editing mode (insert mode):
<Esc> i

# To copy ("yank") or cut ("delete") the current line (paste it with P):
<Esc> yy|dd

# To undo the last operation:
<Esc> u

# To search for a pattern in the file (press n to go to the next result):
<Esc> /search_pattern <Enter>

# To perform a regex substitution in the whole file (from the start, 1, to the end, $):
<Esc> :1,$s/pattern/replacement/g <Enter>

# To save (write) the file, and quit vim:
<Esc> :wq <Enter>

# To exit the file, and quit without saving:
<Esc> :q! <Enter>