If you have two things to do, do them as two things. First find the first string, then as a second thing find the second string. Consider:

#!/usr/bin/perl
use strict;
use warnings;

my $str1 = 'through a file';
my $str2 = 'string';
my $lastStr2Line;

1 while <DATA> !~ m/$str1/;

m/$str2/ and $lastStr2Line = $. while $_ = <DATA>;

die "String 2 '$str2' not found\n" if ! defined $lastStr2Line;
print "String 2 last found on line $lastStr2Line\n";

__DATA__
Here's a good one. Looking to read through a file and then detect a ce
+rtain
string. Then check again sometime later to detect a different string a
+nd alert
if that different string isn't found. While this string could appear a
+nywhere in
the file, I would only want the last found string to run this check on
+...
example:
[download]

Prints:

String 2 last found on line 4
[download]