#main Perl file
my $var = 100;
my $filename = "temp.txt";
open my IN, '<', $filename
    or die "Can't read '$filename': $!";
while (defined (my $line = <IN>)) {
    if($line =~ /^#/){
        #execute perl if statement here
         #Do something based on if statement processed
    };
};

## File to be read, temp.txt##
Some random text, not Perl.
#if($var == 100)
  output this text to a file
#endif