sub file_expansion {
        my ($output, $input) = @_; 
        my $test = $output;     # For testing whether I need to append to an array or a scalar#
        while (<@$input>) { 
                if (-e $_) {
                        open (FILE, "< $_");
                        my @lines = <FILE>;
                        foreach my $line (@lines) {
                                $_ = $test;
                                if (/SCALAR/) {
                                        $output .= $line;
                                        
                                }
                                else {
                                        push @$output, $line;
                                }
                        }
                }
                else {
                        print "<<ERROR: File \'$_\' doesn't exist or can't be read.>>";
                }
        }
}

@temp_fyle = "/home/monkey/list_of_commands"; (looks like below:
interface blah 
ip address 1.2.3.4 255.255.255.255
)

&file_expansion(\$template,\@temp_fyle);