WordPress at a glance
function is not described

get_blog_id_from_url() WP 3.0.0

Get a blog's numeric ID from its URL.

On a subdirectory installation like example.com/blog1/, $domain will be the root 'example.com' and $path the subdirectory '/blog1/'. With subdomains like blog1.example.com, $domain is 'blog1.example.com' and $path is '/'.

  • Global. wpdb. $wpdb WordPress database abstraction object.

No Hooks.

Return

Int. 0 if no blog found, otherwise the ID of the matching blog

Usage

get_blog_id_from_url( $domain, $path );
$domain(string) (required)
$path(string)
Not required for subdomain installations.
Default: '/'

Code of get blog id from url: wp-includes/ms-functions.php VER 5.1.1

<?php
function get_blog_id_from_url( $domain, $path = '/' ) {
	$domain = strtolower( $domain );
	$path   = strtolower( $path );
	$id     = wp_cache_get( md5( $domain . $path ), 'blog-id-cache' );

	if ( $id == -1 ) { // blog does not exist
		return 0;
	} elseif ( $id ) {
		return (int) $id;
	}

	$args   = array(
		'domain' => $domain,
		'path'   => $path,
		'fields' => 'ids',
		'number' => 1,
	);
	$result = get_sites( $args );
	$id     = array_shift( $result );

	if ( ! $id ) {
		wp_cache_set( md5( $domain . $path ), -1, 'blog-id-cache' );
		return 0;
	}

	wp_cache_set( md5( $domain . $path ), $id, 'blog-id-cache' );

	return $id;
}