PHP: Using a variable inside a double quotes with backshlashes - php

Question

I have a variable with Windows path and backslahes. And in this i need two antoher variables. Looks like this:
$file_name_with_full_path = 'C:\inetpub\wwwroot\upload\files\$filnr\$file';
At the end i need the variable $filnr and $file, but it is not possible to do it with " "
$file_name_with_full_path = "C:\inetpub\wwwroot\upload\files\$filnr\$file";
With " " i got an error, because in my script i do a curl-request.
How can i insert the variables with backslash in a single ' ?
my full script looks like this:
if ($result->num_rows > 0) {
//schleife ausführen
while($row = $result->fetch_assoc()) {
//ip und filnr aus datenbank in var
$ip = $row["ip"];
$filnr = $row["filnr"];
echo "$filnr $ip<br>";
//filnr und dateiname momentan noch hart codiert
$target_url = "http://10.74.20.94:6001/upload";
$file_name_with_full_path = 'C:\inetpub\wwwroot\upload\files\$filnr\$file';
if (function_exists('curl_file_create')) {
$cFile = curl_file_create($file_name_with_full_path);
} else {
$cFile = '#' . realpath($file_name_with_full_path);
}
$post = array('targetpath'=>'C:\bizstorecard\hossi','uploadfile'=> $cFile);
$go = curl($target_url,$post);
}
} else {
echo "Fehler bei Abfrage";
}
function curl($target_url,$post) {
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$target_url);
curl_setopt($ch, CURLOPT_POST,1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
curl_exec($ch);
curl_close($ch);
}

Answer 1

Just use string concatenation instead:
$file_name_with_full_path = 'C:\inetpub\wwwroot\upload\files\\' . $filnr . '\\' . $file;
Note you need to use \\ for the \ before the ' otherwise PHP treats it as an escaped '.
If you want to use double quotes, you just need to escape all the backslashes that occur before something that can be interpreted as a variable (or a special character e.g. \f = Formfeed):
$file_name_with_full_path = "C:\inetpub\wwwroot\upload\\files\\$filnr\\$file";
Demo on 3v4l.org

Answer 2

You cannot use variables directly in a single quoted string, if you want to use this you need to either concatenate manually or use sprintf.
The reason the double quotes aren't working is because the backslash escapes the $ character and so it just prints the string literally. You need to escape the backslash characters to print them correctly.
$file_name_with_full_path = "C:\\inetpub\\wwwroot\\upload\\files\\$filnr\\$file";

Answer 3

Alternatively, and with added readability, you can use curly braces inside double-quoted strings.
$path = "C:\inetpub\wwwroot\upload\files\{$filnr}\{$file}";
Additionally, this works with array values addressed using single quotes:
$path = "C:\inetpub\wwwroot\upload\files\{$file['directory']}\{$file['name']}";