php does not detect subfolders and files

  mysql, mysqli, php

the php file and the folder are in the same directory, when I check the path that includes a subfolder and a file it shows that the file does not exist. but the path if it is in the windows explorer if it exists.


if (!empty($_GET['copia']) ){
    $consultar1 = mysqli_query($conexion,"SELECT * FROM documentos" );
    $total = mysqli_num_rows($consultar1);
    if($total > 0){
        if (!file_exists("copia_seguridad")) {
        while ( $doct = mysqli_fetch_row($consultar1)){
            $consultar_categoria = mysqli_query($conexion,"SELECT nombreCategoria FROM categorias");
            $subdirectory = mysqli_fetch_array($consultar_categoria);
            $longitud = count($subdirectory);
            for($i=0; $i<$longitud; $i++){
            $nombre_fichero = 'documentos/$subdirectory[$i]/".$doct[1].';
            if (file_exists($nombre_fichero)) {
               echo "El fichero $nombre_fichero existe";
             } else {
               echo "El fichero $nombre_fichero no existe";

        echo  "<script> alert('Copia de Seguridad realizada...'); </script>";
        echo "<script>document.location.href = 'admin.php'; </script>";
        echo  "<script> alert('No hay documentos para guardar...'); </script>";
        echo "<script>document.location.href = 'admin.php'; </script>";

windows explorer path

error with "

error with ‘

change the double quotes in the path to a single quote but it still doesn’t detect the file.

How should the path be built for php to detect subfolders and files?

Source: Ask PHP