php keep only the first 4 lines of a text file when uploading

Question

I'm using the following code to upload a txt file to my server..

<form style="margin-bottom:2px;" method="post" enctype="multipart/form-data" name="formUploadFile">     
            <label>Select txt file to upload:</label>
            <br>
            <input type="file" name="files[]" /> <input type="submit" value="Upload" name="Submit"/>
            <br>
        </form> 

        <?php
            if(isset($_POST["Submit"]))
            {
                $errors = array();
                $uploadedFiles = array();
                $extension = array("txt");
                $bytes = 1024;
                $KB = 1024;
                $totalBytes = $bytes * $KB;
                $UploadFolder = "tmp_txt_store";

                $counter = 0;

                foreach($_FILES["files"]["tmp_name"] as $key=>$tmp_name){
                    $temp = $_FILES["files"]["tmp_name"][$key];
                    $name = $_FILES["files"]["name"][$key];

                    if(empty($temp))
                    {
                        break;
                    }

                    $counter++;
                    $UploadOk = true;

                    if($_FILES["files"]["size"][$key] > $totalBytes)
                    {
                        $UploadOk = false;
                        array_push($errors, $name." file size is larger than the 1 MB.");
                    }

                    $ext = pathinfo($name, PATHINFO_EXTENSION);
                    if(in_array($ext, $extension) == false){
                        $UploadOk = false;
                        array_push($errors, $name." invalid file type.");
                    }

                    if(file_exists($UploadFolder."/".$name) == true){
                        $UploadOk = false;
                        array_push($errors, $name." file already exists.");
                    }

                    if($UploadOk == true){
                        $name = "my.txt";
                        move_uploaded_file($temp,$UploadFolder."/".$name);
                        array_push($uploadedFiles, $name);
                    }

                }

                if($counter>0){
                    if(count($errors)>0)
                    {
                        echo "<b>Errors:</b>";
                        foreach($errors as $error)
                        {
                            echo " ".$error.",";
                        }
                        echo "<br/>";
                    }

                    if(count($uploadedFiles)>0){
                        echo "<b>Uploaded:</b>";
                        echo "=";
                        foreach($uploadedFiles as $fileName)
                        {
                            echo " ".$fileName.",";
                        }
                        echo "<br/>";

                        echo "DONE!";
                                            }                                           
                }
                else{
                    echo "ERROR: Please press the browse button and select a txt file to upload.";
                }

            }
        ?>

And I would like to keep only the first 4 lines of text, so trim off (delete) all lines of text (after the 4th line) before it gets uploaded.

So

line 1 text
line 2 text
line 3 text
line 4 text
line 5 text
line 6 text
line 7 text
<!--And so on-->

Becomes

line 1 text
line 2 text
line 3 text
line 4 text

How do I go about doing this? I have tried a few suggstions looking at answers to other (similar) questions but being a so novice at php I'm really not getting anywhere with this.

Answer 1

You can just read the first four line, then overwrite the file.

    $fp = fopen($file_path);
    $num = 4;
    while($num-- > 0 && $line = fgets($fp)){
        $lines [] = $line;
    }
    fclose($file_path);
    file_put_contents($file_path,join("",$lines));