<div>
You may find regular expressions easier to understand (decipher) if you write them like this -- with comments and explanations.<br />

<pre><code id="code-20-40398331-1">$rgx
= '#'        // REGEX DELIMITER
. '^'        // AT START OF STRING
. '['        // START CHARACTER CLASS
. '0-9'      // RANGE OF CHARACTERS 0-9
. ']'        // END OF CHARACTER CLASS 
. '{4}'      // EXACTLY FOUR OF THESE IN THE CLASS
. '[A-Z]'    // A CHARACTER CLASS OF ALPHABETIC CHARACTERS
. '{1}'      // EXACTLY ONE OF THESE IN THE CLASS
. '$'        // AT THE END OF THE STRING
. '#'        // REGEX DELIMITER
. 'i'        // OPTIONAL - CASE-INSENSITIVE
;</code></pre>
</div>


You may find regular expressions easier to understand (decipher) if you write them like this -- with comments and explanations.


$rgx
= '#'        // REGEX DELIMITER
. '^'        // AT START OF STRING
. '['        // START CHARACTER CLASS
. '0-9'      // RANGE OF CHARACTERS 0-9
. ']'        // END OF CHARACTER CLASS 
. '{4}'      // EXACTLY FOUR OF THESE IN THE CLASS
. '[A-Z]'    // A CHARACTER CLASS OF ALPHABETIC CHARACTERS
. '{1}'      // EXACTLY ONE OF THESE IN THE CLASS
. '$'        // AT THE END OF THE STRING
. '#'        // REGEX DELIMITER
. 'i'        // OPTIONAL - CASE-INSENSITIVE
;

<div>
<div class="content wysiwyg-content">
I need to validate a string for these criteria...<br />
<br />
Must be 5 characters<br />
First 4 characters must be 0-9<br />
Fifth character must be A-Z<br />
<br />
How do I make this work?<br />
<br />
$name = test_input($_POST[&quot;name&quot;])<wbr />;<br />
if (!preg_match(&quot;/^[0-9] {4} [A-Z] {1}$/&quot;,$name)) {<br />
&nbsp; $nameErr = &quot;not allowed&quot;; <br />
}
</div>
</div>


I need to validate a string for these criteria...

Must be 5 characters
First 4 characters must be 0-9
Fifth character must be A-Z

How do I make this work?

$name = test_input($_POST["name"]);
if (!preg_match("/^[0-9] {4} [A-Z] {1}$/",$name)) {
  $nameErr = "not allowed"; 
}

PHP preg_match

PHP is a widely-used server-side scripting language especially suited for web development, powering tens of millions of sites from Facebook to personal WordPress blogs. PHP is often paired with the MySQL relational database, but includes support for most other mainstream databases. By utilizing different Server APIs, PHP can work on many different web servers as a server-side scripting language.