Connect using Connection Service File

For those who already have their Connection Service Files setup, it is
useful not to have
to specify the configuration file.
By connection using the service=<name> format we delegate all the
resolving of service file
locations to libpq.

README.rst

@@ -69,7 +69,7 @@ By default, pg_view tries to autodetect all PostgreSQL clusters running on the s
 - checks all arguments, picking the first that allows it to establish a connection
 - if pg_view can't get either the port/host or port/socket_directory pair, bail out
 
-If the program can't detect your connection arguments using the algorithm above, you can specify those arguments manually using the configuration file supplied with the -c option. This file should consist of one or more sections, each containing a key = value pair.
+If the program can't detect your connection arguments using the algorithm above, you can specify those arguments manually using the configuration file supplied with the -c option. This file should consist of one or more sections, each containing a key = value pair. You can also use your Connection Service File.
 
 The title of each section represents a database cluster name (this name is for display purposes only). The dbname parameter is `postgres` by default, and specifies the actual name of the database to connect to. The key-value pairs should contain connection parameters.
 

pg_view/__init__.py

@@ -204,6 +204,9 @@ def main():
             if not establish_user_defined_connection(instance, conn, clusters):
                 logger.error('failed to acquire details about ' +
                              'the database cluster {0}, the server will be skipped'.format(instance))
+    elif options.instance:
+        if not establish_user_defined_connection(options.instance, {'service': options.instance}, clusters):
+            logger.error("unable to continue with cluster {0}".format(options.instance))
     elif options.host:
         # try to connet to the database specified by command-line options
         conn = build_connection(options.host, options.port, options.username, options.dbname)