(PHP 5)
pg_version — Returns an array with client, protocol and server version (when available)
$connection
  ] )pg_version() returns an array with the client, protocol and server version. Protocol and server versions are only available if PHP was compiled with PostgreSQL 7.4 or later.
For more detailed server information, use pg_parameter_status().
connection
       PostgreSQL database connection resource.  When 
       connection is not present, the default connection 
       is used. The default connection is the last connection made by 
       pg_connect() or pg_pconnect().
      
   Returns an array with client, protocol 
   and server keys and values (if available).  Returns
   FALSE on error or invalid connection.
  
Example #1 pg_version() example
<?php
  $dbconn = pg_connect("host=localhost port=5432 dbname=mary")
     or die("Could not connect");
     
  $v = pg_version($dbconn);
  
  echo $v['client'];
?>
The above example will output:
7.4