Vi[m] [classic]

While in command mode (case sensitive)

• move the cursor with arrow keys; if there aren't any arrow keys, use j,k,h,l
• i - change to insert mode (before cursor)
• a - change to insert mode (after cursor)
• A - change to insert mode (at end of line)
• r - replace one character
• R - overwrite text
• x - delete one character
• dd - delete one line
• yy - yank line (copy)
• p - paste deleted or yanked text after cursor
• P - paste deleted or yanked text before cursor
• G - go to end of the file
• 1G - go to top of the file
• J - merge next line with this one
• / - search, follow / with text to find
• :wq - write file and quit
• :q! - quit without saving
• :%s/old/new/g - substitute; replace "old" with "new" on all lines
• :g/pattern/d - delete all lines that match the pattern

While in insert mode

• ESC - change to command mode
• any text typed is entered at the cursor

If you gave vi a whirl and don't dig it, give the nano editor a try.