You can add a line to the end of a file, such as your CONFIG.SYS file, without using an editor if you use the COPY command in the following form:
copy filename.ext + con

This causes MS-DOS to echo the file and CON, with the cursor. Enter the text to be added to the file, then press CTRL+Z and ENTER to end your modification. The following example adds a line to the end of a todo.txt file:
C:\>copy todo.txt + con
(A) @online Research text files
(A) @phone Call shop
^z

1 File(s) copied

If only one line is to be added and that line doesn’t contain any redirection, you can also use the ECHO command as follows:
C:\>echo (B) +SharePoint Create FAQ feature and test >> todo.txt

Check out todo.txt, List your life in .txt, and Living in text files for more information on using a text file to keep track of your own crazy life.