\c :A counter that increments for each statement you issue
\D :The full current date
\d :The default database
\h :The server host
\l :The current delimiter (new in 5.1.12)
\m :Minutes of the current time
\n :A newline character
\O :The current month in three-letter format (Jan, Feb, …)
\o :The current month in numeric format
\P :am/pm
\p :The current TCP/IP port or socket file
\R :The current time, in 24-hour military time (0–23)
\r :The current time, standard 12-hour time (1–12)
\S :Semicolon
\s :Seconds of the current time
\t :A tab character
\U :Your full user_name@host_name account name
\u :Your user name
\v :The server version
\w :The current day of the week in three-letter format (Mon, Tue, …)
\Y :The current year, four digits
\y :The current year, two digits
\_ :A space
\A :space (a space follows the backslash)
\' :Single quote
\" :Double quote
\\ :A literal “\” backslash character
\x :x, for any “x” not listed above