If you just want to ensure a string contains only alphanumeric characters. A-Z, a-z, 0-9 you don't need to use regular expressions.

Use ctype_alnum()

Example from the documentation:

<?php
$strings = array('AbCd1zyZ9', 'foo!#$bar');
foreach ($strings as $testcase) {
    if (ctype_alnum($testcase)) {
        echo "The string $testcase consists of all letters or digits.\n";
    } else {
        echo "The string $testcase does not consist of all letters or digits.\n";
    }
}
?>

The above example will output:

The string AbCd1zyZ9 consists of all letters or digits.
The string foo!#$bar does not consist of all letters or digits.

You need to use anchors and a quantifier:

echo preg_match("/^[a-z0-9.]+$/i", $accountname);

Your string +_#luke123* contains a letter and a number, thus there is a match. If we tell the engine to only match the whole string from beginning (^) to end ($), we'll make sure this will not match. + ensures we capture not just 1, but all characters.

See this demo, now there is no match!

EDIT: Since you also need to check these conditions:

string must start with 2 or more letters or numbers and end with 1 or more letters or numbers

I can suggest this ^[a-z0-9]{2,}[a-z0-9.]*[a-z0-9]+$ regex (must be used with i option) that means:

• Starts with 2 or more letters or numbers
• then follow any number of digits, letters or periods
• and ends in 1 or more letters or numbers.

Another demo

Use

preg_match('/^[a-z0-9 .\-]+$/i', $firstname)

You can use the following regular expression:

^[\w ]+$

This matches any combinations of word characters \w and spaces , but as the guys said be careful because some names might contain other symbols.

So you can use it like this:

if (preg_match("/^[\\w ]+$/", $name)) {
    // valid name
}
else {
    // invalid name
}

Use \p{L}, a Unicode letter class, to match any letter from any alphabet (i.e. non-ASCII Unicode letters):

^[\d\s\p{L}]+$

Demo: https://regex101.com/r/wfjCjF/3

P.S.

Mind the pattern delimiters when using a regex in preg_match:

preg_match('/^[\d\s\p{L}]+$/', 'öäßè')
            ^              ^

It seems the simplest way is just to do it in two regex's.

if (preg_match('/[A-Za-z]/', $myString) && preg_match('/[0-9]/', $myString))
{
    echo 'Contains at least one letter and one number';
}

I suppose another way to do it is this below. It says "a letter and then later on at some point a number (or vice versa)". But the one above is easier to read IMO.

if (preg_match('/[A-Za-z].*[0-9]|[0-9].*[A-Za-z]/', $myString))
{
    echo 'Contains at least one letter and one number';
}

simplest to understand, longest to write

[A-Z][A-Z][0-9][0-9][0-9][0-9][0-9][A-Z][A-Z]

shorter:

[A-Z]{2}[0-9]{5}[A-Z]{2}

complete lines only:

^[A-Z]{2}[0-9]{5}[A-Z]{2}$    // ^ - start of line; $ - end of line

capture in parens:

(^[A-Z]{2}[0-9]{5}[A-Z]{2}$)  // as per mpaepper, for reuse in matched expression

shorter still:

(^[A-Z]{2}\d{5}[A-Z]{2}$)     //  \d represents 0-9

Code:

if(preg_match('/[^a-z_\-0-9]/i', $string))
{
  echo "not valid string";
}

Explanation:

• [] => character class definition
• ^ => negate the class
• a-z => chars from 'a' to 'z'
• _ => underscore
• - => hyphen '-' (You need to escape it)
• 0-9 => numbers (from zero to nine)

The 'i' modifier at the end of the regex is for 'case-insensitive' if you don't put that you will need to add the upper case characters in the code before by doing A-Z

PHP is trying to render the variable $s in the double quoted string. Use single quotes instead and you can remove the {1} inside your regular expression because it is not necessary.

$word = '$1$s';

if (preg_match('/^\$[1-9]\$s$/', $word)) {
    echo 'true';
} else {
    echo 'false';
}

You can also escape the $ in your double quoted string:

$word = "$1\$s";
// Note $1 doesn't need to be escaped since variables can't start with numbers

Finally, you can see why this wasn't working by seeing what your $word actually equaled (with error reporting enabled):

$word = "$1$s"; // Notice: Undefined variable: s on line #
echo $word;     // $1

You wrote you have a regex that allows an input to be either letters a to z and numbers 0 to 9 only, but actually ^[a-zA-Z0-9\'.]{5,30}$ matches a string of 5 to 30 ASCII letters, digits and also ' or ..

If you just want to make your regex match what it matches, but not a string that only consists of digits, use a (?!\d+$) lookahead:

'/^(?!\d+$)[a-z0-9\'.]{5,30}$/i'
   ^^^^^^^^

Note you do not need to specify the A-Z or a-z range if you use a i case insensitive flag (just either of them is enough).

The (?!\d+$) is a negative lookahead that fails the match if there are one or more digits followed by the end of string ($) immediately to the right of the current location (which is the start of the string).

See the regex demo.

If you do not want to match a string that only consists of dots, or ', or digits, use

'/^(?!(?:\d+|([\'.])\1*)$)[a-z0-9\'.]{5,30}$/i'

See another demo.

That would be:

if(preg_match('/[^a-z\s-]/i',$stringabc))

for "anything but letters (a-z), spaces (\s, meaning any kind of whitespace), and dashes (-)".

To also allow numbers:

if(preg_match('/[^0-9a-z\s-]/i',$stringabc))