bash$ sed [options] program [inputfile]
This simple program consists of the command 'd'. It tells sed to delete the pattern buffer.
bash$ sed -e 'd' /etc/hosts
Another command is 'p'. It tells sed to print the pattern buffer. (Every line is printed twice)
bash$ sed -e 'p' /etc/hosts
We don't always want to work on the whole document --> There must be a mechanism to address a line or several lines