pg_connect() returns a connection resource that is needed by other PostgreSQL functions.
pg_connect() opens a connection to a PostgreSQL database specified by the connection_string. It returns a connection resource on success. It returns FALSE if the connection could not be made. connection_string should be a quoted string.
The arguments available for connection_string includes host, hostaddr, port, dbname, user, password, connect_timeout, options, tty (ignored), sslmode, requiressl (deprecated in favor of sslmode), and service. Which of these arguments exist depends on your PostgreSQL version.
If a second call is made to pg_connect() with the same connection_string, no new connection will be established unless you pass PGSQL_CONNECT_FORCE_NEW as connect_type, but instead, the connection resource of the already opened connection will be returned. You can have multiple connections to the same database if you use different connection strings.
The old syntax with multiple parameters $conn = pg_connect("host", "port", "options", "tty", "dbname") has been deprecated.