Improve header output from psql's \watch command.

Include the \pset title string if there is one, and shorten the prefab
part of the header to be "timestamp (every Ns)".  Per suggestion by
David Johnston.

Michael Paquier and Tom Lane

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

@@ -2673,9 +2673,11 @@ testdb=&gt; <userinput>\setenv LESS -imx4F</userinput>
         <term><literal>\watch [ <replaceable class="parameter">seconds</replaceable> ]</literal></term>
         <listitem>
         <para>
-        Repeatedly execute the current query buffer (like <literal>\g</>)
+        Repeatedly execute the current query buffer (as <literal>\g</> does)
         until interrupted or the query fails.  Wait the specified number of
-        seconds (default 2) between executions.
+        seconds (default 2) between executions.  Each query result is
+        displayed with a header that includes the <literal>\pset title</>
+        string (if any), the time as of query start, and the delay interval.
         </para>
         </listitem>
       </varlistentry>

src/bin/psql/command.c

@@ -3020,7 +3020,10 @@ static bool
 do_watch(PQExpBuffer query_buf, long sleep)
 {
 	printQueryOpt myopt = pset.popt;
-	char		title[50];
+	const char *user_title;
+	char	   *title;
+	int			title_len;
+	int			res = 0;
 
 	if (!query_buf || query_buf->len <= 0)
 	{
@@ -3034,19 +3037,38 @@ do_watch(PQExpBuffer query_buf, long sleep)
 	 */
 	myopt.topt.pager = 0;
 
+	/*
+	 * If there's a title in the user configuration, make sure we have room
+	 * for it in the title buffer.
+	 */
+	user_title = myopt.title;
+	title_len = (user_title ? strlen(user_title) : 0) + 100;
+	title = pg_malloc(title_len);
+
 	for (;;)
 	{
-		int			res;
 		time_t		timer;
+		char		asctimebuf[64];
 		long		i;
 
 		/*
-		 * Prepare title for output.  XXX would it be better to use the time
-		 * of completion of the command?
+		 * Prepare title for output.  Note that we intentionally include a
+		 * newline at the end of the title; this is somewhat historical but it
+		 * makes for reasonably nicely formatted output in simple cases.
 		 */
 		timer = time(NULL);
-		snprintf(title, sizeof(title), _("Watch every %lds\t%s"),
-				 sleep, asctime(localtime(&timer)));
+		strlcpy(asctimebuf, asctime(localtime(&timer)), sizeof(asctimebuf));
+		/* strip trailing newline from asctime's output */
+		i = strlen(asctimebuf);
+		while (i > 0 && asctimebuf[--i] == '\n')
+			asctimebuf[i] = '\0';
+
+		if (user_title)
+			snprintf(title, title_len, _("%s\t%s (every %lds)\n"),
+					 user_title, asctimebuf, sleep);
+		else
+			snprintf(title, title_len, _("%s (every %lds)\n"),
+					 asctimebuf, sleep);
 		myopt.title = title;
 
 		/* Run the query and print out the results */
@@ -3056,10 +3078,8 @@ do_watch(PQExpBuffer query_buf, long sleep)
 		 * PSQLexecWatch handles the case where we can no longer repeat the
 		 * query, and returns 0 or -1.
 		 */
-		if (res == 0)
+		if (res <= 0)
 			break;
-		if (res == -1)
-			return false;
 
 		/*
 		 * Set up cancellation of 'watch' via SIGINT.  We redo this each time
@@ -3084,7 +3104,8 @@ do_watch(PQExpBuffer query_buf, long sleep)
 		sigint_interrupt_enabled = false;
 	}
 
-	return true;
+	pg_free(title);
+	return (res >= 0);
 }
 
 /*