php-regexHow to use PHP regex to match letters, numbers and underscores?

Using PHP regex to match letters, numbers and underscores is a common task. The following example code block shows how to do this:

$string = 'abc123_ABC';
$pattern = '/^[a-zA-Z0-9_]+$/';

if (preg_match($pattern, $string)) {
    echo 'Matched!';
} else {
    echo 'Not matched!';
}

The output of the example code is:

Matched!

Code explanation

• $string = 'abc123_ABC';: This is the string to be tested.
• $pattern = '/^[a-zA-Z0-9_]+$/';: This is the regular expression pattern used to match letters, numbers and underscores. The pattern /^[a-zA-Z0-9_]+$/ means that the string should start with a letter, number or underscore, and end with a letter, number or underscore.
• preg_match($pattern, $string): This is the function used to match the string against the pattern.
• if (preg_match($pattern, $string)) {: This is the condition used to check if the string matches the pattern.
• echo 'Matched!';: This is the output if the string matches the pattern.
• echo 'Not matched!';: This is the output if the string does not match the pattern.

Helpful links

• PHP Regular Expression Functions
• Regular Expressions Tutorial

Edit this code on GitHub