editing a file via a shell script ??

Morning All: I know this might be easy but since I don't do this very often I get stumped real quick... Sun box Solaris 8 ksh...

I need to edit a file via a shell script. In this file I need to locate one specific line and then remove that line plus the next 20 line below that....
Any suggestions on where to start?? I could use sed to search for the first line in question.. but not sure what to do after that.

sed '/matching line/{;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;d;}'

Sorry for posting my first answer before testing it. Actually I misread the question at first.

Sweet.... Works like a champ !!
This was done from inside a script to I had to replace the ' with a "

sed "/$delnode/{;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;d;}" myfile