WordPress函数：is_email 检查 email 有效性

函数原型：

is_email( string $email, bool $deprecated = false ): string|false

验证电子邮件是否有效。

参数说明：

$email 要检查的邮件地址。

函数源码：

function is_email( $email, $deprecated = false ) {
	if ( ! empty( $deprecated ) ) {
		_deprecated_argument( __FUNCTION__, '3.0.0' );
	}

	// Test for the minimum length the email can be.
	if ( strlen( $email ) < 6 ) {
		return apply_filters( 'is_email', false, $email, 'email_too_short' );
	}

	// Test for an @ character after the first position.
	if ( strpos( $email, '@', 1 ) === false ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'is_email', false, $email, 'email_no_at' );
	}

	// Split out the local and domain parts.
	list( $local, $domain ) = explode( '@', $email, 2 );

	// LOCAL PART
	// Test for invalid characters.
	if ( ! preg_match( '/^[a-zA-Z0-9!#$%&\'*+\/=?^_`{|}~\.-]+$/', $local ) ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'is_email', false, $email, 'local_invalid_chars' );
	}

	// DOMAIN PART
	// Test for sequences of periods.
	if ( preg_match( '/\.{2,}/', $domain ) ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'is_email', false, $email, 'domain_period_sequence' );
	}

	// Test for leading and trailing periods and whitespace.
	if ( trim( $domain, " \t\n\r\0\x0B." ) !== $domain ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'is_email', false, $email, 'domain_period_limits' );
	}

	// Split the domain into subs.
	$subs = explode( '.', $domain );

	// Assume the domain will have at least two subs.
	if ( 2 > count( $subs ) ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'is_email', false, $email, 'domain_no_periods' );
	}

	// Loop through each sub.
	foreach ( $subs as $sub ) {
		// Test for leading and trailing hyphens and whitespace.
		if ( trim( $sub, " \t\n\r\0\x0B-" ) !== $sub ) {
			/** This filter is documented in wp-includes/formatting.php */
			return apply_filters( 'is_email', false, $email, 'sub_hyphen_limits' );
		}

		// Test for invalid characters.
		if ( ! preg_match( '/^[a-z0-9-]+$/i', $sub ) ) {
			/** This filter is documented in wp-includes/formatting.php */
			return apply_filters( 'is_email', false, $email, 'sub_invalid_chars' );
		}
	}

	// Congratulations, your email made it!
	/** This filter is documented in wp-includes/formatting.php */
	return apply_filters( 'is_email', $email, $email, null );
}

可以看出，这个函数还是很复杂的。所以，在 WordPress 中最好使用 is_email 函数，不必自己造轮子了。

包含钩子：

apply_filters( 'is_email', string|false $is_email, string $email, string $context )

使用举例：

if ( is_email( 'email@domain.com' ) ) {
	echo 'email address is valid.';
}