Upload error checking

[Anon]

I've got an upload form which works. However, it will overwrite an existing file if the name is a duplicate. I wanted to do a check for the file, and if the name is already used, send them back to choose a different name. However, the code doesn't seem to work. All upload attempts work and existing files are overwritten. Here's the relevant code.

if (file_exists("documents/$filename.$filetype")) {
printf("Filename already exists. Please click Back and choose a different filename.");
} else {
copy($file,"documents/$filename.$filetype");
odbc_exec($db, "INSERT INTO content (posting_date, content_author, content_email, content_title, content_file, content_body) VALUES ('$date', '$author', '$email', '$title', '$filename.$filetype', '$comment')");
}

What's wrong?

[Anon]

I wrote an upload function in one of my scripts so I will include it here hoping you find it useful. It was my first PHP project so it probably isn't written that well, I haven't come across the copy function so that might of been a better way to do it but what follows works so I hope you find it useful.

The following code does use variable variables hence the ${$filename} and also is used in a class so I hope it isn't to confusing. I also use a dienice function that prints an appropriate error message then exits the script.

#
# This is upload get value. It saves the uploaded file in the upload directory
function getValue() {
    global $uploadDir;
global ${$this->name}; # This is the file that has been saved in the tmp dir
    $size = $this->name . "_size"; # This is the filesize in bytes
    $filename = $this->name . "_name"; # This is the original file name
    global ${$size};
    global ${$filename};

    # If a file has been uploaded already and we are uploading another one then
    # delete the original. Otherwise if there is no new file return the old one.
if ($this->value && ${$filename}) {
    unlink("$uploadDir/$this->value");
} else if (!${$filename}) {
    return "$this->value";
}

    # If a file of this name already exists print an error message and cancel.
    # We don't want to overwrite the existing file
    if (file_exists("$uploadDir/${$filename}")) {
    $this->dienice("File <i>$uploadDir/${$filename}</i> exists. Will not overwrite");
}

    # This is where the file save occurs. Open the temporary file and read it's 
    # contents. Then write the contents out to the final destination
$writefd = fopen("$uploadDir/${$filename}", "wb");
if (!$writefd) {
    $this->dienice("Unable to open file $uploadDir/${$filename}");
}
$readfd = fopen(${$this->name}, "rb");
if (!$readfd) {
    $this->dienice("Unable to upload file ${$filename}");
}

$contents = fread($readfd, ${$size});
fwrite($writefd, $contents);

fclose($readfd);
fclose($writefd);

return ${$filename};
}