On that line of your code  $url = str_replace(' ','',$url); returns a Random url of one of the files txt of the directory  pasta as an example www.site.com/nome/juliana.html
Right after you use  file_get_contents; whose purpose is to read the contents of a file. Only you are trying to read the contents of a url  file_get_contents($url); since $url returns for example www.site.com/nome/juliana.html and this will only generate an error and nothing more.
Warning:  file_get_contents(www.site.com/nome/juliana.html): 
failed to open stream: No such file or directory in .....
So remove that line from your code that serves nothing but generating one  Warning.
If you already have a url to redirect, I don’t understand why the list of urls  
<li class="ohyeah">
  .............
  .............
</li>
You should have your reasons there and therefore to do this you can use the code below.
$conteudoLista="";
$arr="";
$i=1;
$pasta = 'pasta/';
$diretorio = dir($pasta);
while($arquivo = $diretorio -> read()){
    if (file_exists($pasta.$i.".txt")) {
        $f = file($pasta.$i.".txt");
            foreach($f as $item){
               $arr .= $item .",";
               $strDir = str_replace(".html","",$item); 
               $nome = substr($strDir, 18);
               $conteudoLista .="<a href='http://".$item."'>".$nome."</a><br>"; 
               $conteudoLista = preg_replace( "/\r|\n/", "", $conteudoLista );
            }
    }
$i=$i+1;
}
$diretorio -> close();
$enderecos = (substr($arr,0,-1)); 
$partes = explode(',',$enderecos);
$qtd = count($partes);
$numRnad = (rand(1,$qtd));
$result=$partes[$numRnad];
echo "<li class=\"ohyeah\">".$conteudoLista."</li>";
echo "<br>";
echo "link random : ".$result;
Explaining:
$pasta = 'pasta/' - directory relative path
dir() - With this function, we will read the folder directory and, using the read() method, we will list all the existing files in this directory.
$diretorio = dir($pasta) - read the directory
while($arquivo = $diretorio -> read()) - iteration to go through the files by listing them with the read method()
if (file_exists($pasta.$i.".txt")) - make a check to know if the file exists
foreach($f as $item) - iteration in which $item receives the value of each array item
$arr .= $item ."," - concatenating each item separated by comma
str_replace - to remove (replace) the . html extension from the urls
substr($strDir, 18) - Extract a part of a string - returns the part of the url from position 18 to the end, i.e., eliminates - www.site.com/name/ - which is common to all urls
preg_replace( "/\r|\n/", "", $conteudoLista ) - performs a search for a regular expression and replaces it -  n line break and r car return
substr($arr,0,-1) - removing the last $arr comma
$partes = explode(',',$enderecos)- Let’s separate the $addresses string in all comma occurrences
$qtd = count($partes)- get the number of elements that make up the $parts array
$numRnad = (rand(1,$qtd)) - generates a random number between 1 and the number of elements in the $parts array
$result=$partes[$numRnad] - returns the value of the $numRnad position of the $parts array
$diretorio -> close() - close the reading
Documentation used
							
							
						 
What’s the point of this? Why so many redirects?
– Woss
Play everything for an array, and then do an array_rand
– Don't Panic
@Andersoncarloswoss, for a URL sharing system. The content of the site is not saved in a database so for me to capture the urls the way I need to... it’s the easiest way I could find.
– Marcelo
@Everson, I don’t know enough. Can you help me?
– Marcelo
I’ll edit the question to make it easier. A moment.
– Marcelo
Put html content with urls here to help you. Edit your Question to keep cohesion !
– Rafael Salomão
@Rafaelsalomão, made!
– Marcelo
Honestly, I still don’t understand. All the files
.txthave a URL, and within each URL has a reference to a.htmland in this HTML, they all have the tag<li class="ohyeah">?– Don't Panic
@Everson, exact. I already get the URL inside the txt file. Now I need to search A single url inside the <li tag and redirect the user to it.
– Marcelo