Allow only capital and small letters - php

Question

I would like to accept only small and capital letters from the user.
I tried the below code, it echoes the invalid character message but doesn't work. I mean it doesn't check. It just displays the message. Any help?
<form action="" method="post">
<input type="text" name="fname">
<input type="submit" value="Send" name="submit">
</form>
Update: this is what I have to check and insert the name to database. if numbers found in the name reject the name by displaying the error message else if the name contains only letters insert it into database. That's all I want to acheive.
<?php
if ( isset( $_POST['submit'] ) ) {
$fname = $_POST["fname"];
if(!preg_match ('/^([a-zA-Z]+)$/', $fname)){
echo "Invalid characters";
}
if (empty($fname)) {
echo '<span> First name is required</span>';
}
else{
$mysqli = new mysqli("localhost", "root", "", "test");
$stmt = $mysqli->prepare("INSERT INTO test (firstname) VALUES (?)");
$stmt->bind_param("s", $fname);
$stmt->execute();
$stmt->close();
$mysqli->close();
}
}
?>

Answer 1

If you just want to check you could use ctype_alpha() but you said you want to ACCEPT only letters so if you choose to accept the input you could:
$fname=preg_replace('/[^a-z]/i','',$fname);
better after the check

Answer 2

if(!isset($_POST['fname']) || !ctype_alpha($_POST['fname'])){
// can i haz alpha letters only?
}
(reference)

Answer 3

There are several issues with the code, and the one you are stuck with is probably that you have the form and its processing in the same PHP file. That’s possible, but it requires a different approach. For a starter, it’s probably better to separate them.
What happens with the code posted is that the PHP processor tries to process the form data when no form has been submitted, without even checking for the presence of the data. Now $fname is undefined, so the test always fails.
The test is wrong, too. Now it only checks whether $fname contains at least one letter. For example, if(!preg_match ('/^[a-zA-Z]+$/', $fname)) would test that $fname consists of one or more Ascii letters and nothing else.

Answer 4

use this , this is giving me correct answer
if(!preg_match ('/^([a-zA-Z]+)$/', $fname)){
echo "Invalid characters";
}
else{
echo "correct";
}

Answer 5

The general idea of checking for characters that don't match the [a-zA-Z] pattern is a good one.
However, the "not" part of your if condition is in the wrong place if you want this to work. What you've got now just makes sure that any single character in fname is an upper- or lower-case Latin letter.
You want to push the "not" part of the logic into the pattern:
if (preg_match('/[^a-zA-Z]/', $fname)) {
This checks if any character in fname is not a Latin letter, which is what you're trying to do.
Edit: Your new update has a different test that also works (it appears to be from sourcecode's updated answer, but you've got several tests from the different answers here that will work equally well). But, your updated post makes it clear that your problem isn't really with the pattern for testing the name.
Your code looks like this:
if (/* invalid fname */) {
echo "Invalid characters";
}
if (/* empty fname */) {
echo '<span> First name is required</span>';
}
else {
/* insert into database */
}
That else clause only depends on the the if that comes immediately before it: the check whether fname is empty. In other words, regardless of the result of your check against the characters of fname, you insert it into the database whenever it's not empty.
One easy way to fix this is to just change your second if to an elseif. This will chain all three conditionals together, so the final else block will only occur if both of the earlier conditionals that print error messages weren't triggered.
if (/* empty fname */) {
echo 'First name is required.';
}
elseif (/* invalid fname */) {
echo 'Invalid characters';
}
else {
/* insert into database */
}