Add psql PROMPT variable showing the pid of the connected to backend.

The substitution for the pid is %p.

Author: Julien Rouhaud
Discussion: 116262CF971C844FB6E793F8809B51C6E99D48@BPXM02GP.gisp.nec.co.jp

src/bin/psql/prompt.c

@@ -34,6 +34,7 @@
  * %M - database server "hostname.domainname", "[local]" for AF_UNIX
  *		sockets, "[local:/dir/name]" if not default
  * %m - like %M, but hostname only (before first dot), or always "[local]"
+ * %p - backend pid
  * %> - database server port number
  * %n - database user name
  * %/ - current database
@@ -161,6 +162,15 @@ get_prompt(promptStatus_t status)
 					if (pset.db)
 						strlcpy(buf, session_username(), sizeof(buf));
 					break;
+					/* backend pid */
+				case 'p':
+					if (pset.db)
+					{
+						int pid = PQbackendPID(pset.db);
+						if (pid)
+							snprintf(buf, sizeof(buf), "%d", pid);
+					}
+					break;
 
 				case '0':
 				case '1':