General UNIX puzzle

[Eric Anderson]

> 1) Delete the Nth line from a text file?
> 2) Insert a specified line in a file after the Nth line, leaving the 
> rest of the text the same?
> 3) Delete the first line containing a particular string?
> 4) Insert a specified line after the first line containing a 
> particular string, leaving the rest of the file the same?


You should do your own Comp Sci homework. This looks like (especially 
considering the time of th year) the begining of a Unix Basics course.