I don't use perl for things for which there are standard unix utils.

$ cat text
first
second
third
fourth
fifth
sixth
seventh
eighth
$ cat nums
1
4
6
7
$ ed -s text < nums
first
fourth
sixth
seventh
[download]

Update: this sucks if the text file is too large to load in memory. In that case,

Update: here's a perl solution too:

perl -we 'open N, "<", shift or die; $p = 0; while(defined($n = <N>)) 
+{ $s = <> for $p + 1 .. $n + 0; print $s; $p = $n; }' nums text
[download]

Update: if anyoune knows how to convert the above snippet so that it uses either $. or IO::Handle::input_line_number, please reply me, cause I can't figure out how to do that.