File I/O, find line?

[Joe Seeley <joiey.seeley@...>]

I'm pretty new to Lua, and am using the I/O API for the first time.  I
am currently trying to read/write ini files for an application that I
support.  The file has parameters similar to this.

[subset1]
param1=foo
param2=foo2

[subset2]
param1=foobar
param2=foobar2

What I would like to do is find if certain parameters are defined for
different subsets.  I am able to find my line range by locating the
subset title and then the next blank line following it.  I then want
to find my matching parameter that falls inside that range.  The way I
would like to do this is with a function like so

FindLineInFile_Range(filename,desired_line,start_of_range,end_of_range)
        -- code here....
        if line_found then
             return line_number
        else
             return nil
         end
end

The problem that I am running into is that the only file offset I have
encountered is a character offset via file:seek("set", charOffset).

Is there an easy way to offset directly to the lines I desire?

Thanks so much in advance!

Joe