Or you could just use the toolbox.

$ sed -n 10,20p somefile
$ sed -n 40,/foo/p somefile
$ sed -n /foo/,/bar/p somefile
[download]

Although that's less fun I suppose. Fine, let's do it in Perl.

$ perl -ne'print if 10 .. 20' somefile
$ perl -ne'print if 40 .. /foo/' somefile
$ perl -ne'print if /foo/ .. /bar/' somefile
[download]