How could I go through a file in php and search line by line for a phrase

I am learning to program in this language and I have a problem, I can not extract the line that contains a particular phrase.

I leave the code in case you can help me or guide me a little, since it only prints false and never finds the searched text

<?php
    $ruta = "\\x-wing\logs\"; //ruta actual
    echo listarArchivos($ruta);

    function listarArchivos( $path ){
        $dir = opendir($path);
        $files = array();
        while ($elemento = readdir($dir)){
            if( $elemento != "." && $elemento != ".."){
                if(is_dir($path.$elemento)){
                    listarArchivos( $path.$elemento.'/' );
                }
                else
                {
                    $files[] = $elemento;
                }
            }
        }
        echo $path."<br>";

        for($x=0; $x<count( $files ); $x++){
            $fila = $path.$files[$x];
            echo $files[$x]."<br> ";
            $fp = fopen($fila,"r"); 
            while(!feof($fp)) {
                $linea = fgets($fp);
                if(stristr($linea, "Respaldo terminado") == TRUE){
                    echo $linea. "<br>";
                } else {
                    echo 'Falso';
                }
            }
            fclose($fp);
        }
        echo "<BR>";
    }
?>