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

doc/src/sgml/ref/psql-ref.sgml

@@ -3364,6 +3364,13 @@ testdb=&gt; <userinput>INSERT INTO my_table VALUES (:'content');</userinput>
         </listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><literal>%p</literal></term>
+        <listitem>
+         <para>The pid of the backend currently connected to.</para>
+        </listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><literal>%&gt;</literal></term>
         <listitem><para>The port number at which the database server is listening.</para></listitem>

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':