the basic unit for change is a line (a string of characters terminated by a newline character). You can give commands to the editor to perform various operations on the lines: lines can be printed (displayed); lines can be changed; new lines can be inserted; existing lines can be deleted; lines can be moved or copied to a different place within the file; substitutions of character strings can be made within a line or group of lines [7, p. 186].
Most people use ed only if the terminal they are using at the time cannot support a screen editor. For this reason, only the most basic commands will be introduced here. More information can be found in [7, pp. 187-219].