Just to be on the safe side, I'd advice you to habitually use the strictures ,this is like the ABS system in a car and can really stabilize you from slipping into errors or typos:

use strict;
use warnings;
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Another advice is to use the three argument form of open and show the open modes your files are accessed under (input, output, appending, piping...),

open (FH, '<', "saved_system.txt");
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A third advice with open is to provide for explanation/clues of errors that could ensue, like if the file couldn't be opened, didn't exist, didn't have access attributes and more importantly if system-errors where involved, these clues can be indicated from $!..

open(FH, '<', 'saved_system.txt')or die("Couldn't open file, $!");
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to read the perlvar documentation for $! from the terminal prompt of your machine, "perldoc perlvar $!"

Update:ikegami posted a wholesome example while I was writing these ideas :)...