pure php prevent html input to save into text file - php

Question

i would like to save all submitted data into text file.
there is a regex looking for any name error, if there is, there should be an error message AND!! that submission should not be captured into the text file.
result now: if i were to hit submit button even with name being numbers, i am able to submit and the error message did show up, however, it is being captured in the text file.
HOW can i stop it from saving the input if the condition is not met?
<p> <span class="required"> text boxes with * are required field </span></p>
<form method="post">
Name: <input type="text" id="name" name="name">
<span class="required"> * <?php echo $nameErr;?></span>
<br><br>
Phone Number: <input type="text" id="phoneno" name="phoneno">
<span class="required"> * <?php echo $phonenoErr;?></span>
<br><br>
E-Mail: <input type="text" id="email" name="email">
<span class="required"> * <?php echo $emailErr;?></span>
<br><br>
<input type="submit" id="submit" name="submit" value="submit"> <!--need to code submit alr will redirect to where-->
</form>
UPDATED MY CODE
if (isset($_POST['submit'])) {
if (empty($_POST["name"])) {
$nameErr = "Name is required";
} else {
$name = $_POST["name"];
// check if name only contains letters and whitespace
if (!preg_match("/^[a-zA-Z-' ]*$/", $name)) {
$nameErr = "Only letters and white space allowed";
}
}
if (empty($_POST["phoneno"])) {
$phonenoErr = "Phone Number is required";
} else {
$phoneno = $_POST["phoneno"];
// check if name only contains letters and whitespace
if (!preg_match("/^[[0-9]{8}]*$/", $phoneno)) {
$phonenoErr = "Please key in 8 digits phone number";
}
}
if (empty($_POST["email"])) {
$emailErr = "Email Address is required";
} else {
$email = $_POST["email"];
// check if name only contains letters and whitespace
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
$emailErr = "Wrong email format";
}
else {
/* to save html input into text file */
$name = "Seller Name: " . $_POST['name'] . "
";
$phoneno = "Phone Number: " . $_POST['phoneno'] . "
";
$email = "E-Mail: " . $_POST['email'] . "
";
$file = fopen("testing.txt", "a");
fwrite($file, $name);
fwrite($file, $phoneno);
fwrite($file, $email);
fclose($file);
}
}

Answer 1

You do not need an else statement. Right now your file checks "is a form submitted or not" and if it's not, then stuff will be saved. That doesn't make sense, right? You want to save only if the form was submitted! So don't use an else condition.
You can use an error variable to check if there is any error in any user input.
if (isset($_POST['submit'])) { //the user put in data and submitted the form
$error = 0; //no error yet
if (empty($_POST["name"])) {
$nameErr = "Name is required";
$error = 1; //now there is an error
} else {
$name = $_POST["name"]; //be aware of security risks like SQL injection
}
//error checking for other inputs in the same way
//If there is no error at all, then save the input into a file
if ($error == 0) {
/* to save html input into text file */
$save = "Seller Name: " . $name;
$save .= "Phone Number: " . $phoneno;
$save .= "E-Mail: " . $email;
$file = fopen("testing.txt", "a");
fwrite($file, $save);
fclose($file);
}
}

Answer 2

You should put your writing file logic inside your success condition, without changing much of your code, it should be something like this:
$nameErr = $phonenoErr = $emailErr = "";
/*condition&regex to all text field*/
if (isset($_POST['submit']))
{
$name = $_POST["name"] ?? "";
if (empty($name)) {
$nameErr = "Name is required";
} else {
// check if name only contains letters and whitespace
if (!preg_match("/^[a-zA-Z-' ]*$/",$name)) {
$nameErr = "Only letters and white space allowed";
}
}
if ($nameErr === "") {
$name = "Seller Name: ".$_POST['name']."";
$phoneno = "Phone Number: ".$_POST['phoneno']."";
$email = "E-Mail: ".$_POST['email']."";
$file=fopen("testing.txt", "a");
fwrite($file, $name);
fwrite($file, $phoneno);
fwrite($file, $email);
fclose($file);
}
}
Also note that there is no checks for other field (phoneno and email), so if they are not set, you will have error!