• File checks
• File test operators check if a file exists, is readable or writable, etc.
• -e tests if file is exists
• -r tests if file is readable
• -w tests if file is writable
• -x tests if file is executable
• -l tests if file is a symlink
• -T tests if file is a text file
• perldoc perlfunc lists more

        my $filename = "pie_recipe";
        if (-r $filename) {
            open INPUT, "> $filename" or die "Can't open $filename: $!";
        } else {
            print "The file $filename is not readable.\n";
        }