Here's a WIP patch for the parenthesized-options route.

I realized that if we make the options be single words in the form
name=value, we can easily handle the shortcut forms with no value.
So that's what this does.

What this does *not* do is offer any solution to the question of
how to put a right paren as the last character of a pset option
value.  I don't really see any easy way to handle that, but maybe
we can punt for now.

Also no docs or test cases, but I see no point in putting effort into
that in advance of consensus that this is what we want.

0001 is some save/restore infrastructure that we'd need for pretty
much all of the proposals on the table, and then 0002 improves the
command itself.

                        regards, tom lane

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index db31fa8..1055af5 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -160,8 +160,8 @@ static void minimal_error_message(PGresult *res);
 
 static void printSSLInfo(void);
 static void printGSSInfo(void);
-static bool printPsetInfo(const char *param, struct printQueryOpt *popt);
-static char *pset_value_string(const char *param, struct printQueryOpt *popt);
+static bool printPsetInfo(const char *param, printQueryOpt *popt);
+static char *pset_value_string(const char *param, printQueryOpt *popt);
 
 #ifdef WIN32
 static void checkWin32Codepage(void);
@@ -1302,7 +1302,11 @@ exec_command_g(PsqlScanState scan_state, bool active_branch, const char *cmd)
 		}
 		free(fname);
 		if (strcmp(cmd, "gx") == 0)
-			pset.g_expanded = true;
+		{
+			/* save settings, then force expanded = 1 */
+			pset.gsavepopt = savePsetInfo(&pset.popt);
+			pset.popt.topt.expanded = 1;
+		}
 		status = PSQL_CMD_SEND;
 	}
 	else
@@ -3785,6 +3789,17 @@ _unicode_linestyle2string(int linestyle)
 /*
  * do_pset
  *
+ * Performs the assignment "param = value", where value could be NULL;
+ * for some params that has an effect such as inversion, for others
+ * it does nothing.
+ *
+ * Adjusts the state of the formatting options at *popt.  (In practice that
+ * is always pset.popt, but maybe someday it could be different.)
+ *
+ * If successful and quiet is false, then invokes printPsetInfo() to report
+ * the change.
+ *
+ * Returns true if successful, else false (eg for invalid param or value).
  */
 bool
 do_pset(const char *param, const char *value, printQueryOpt *popt, bool quiet)
@@ -4109,9 +4124,11 @@ do_pset(const char *param, const char *value, printQueryOpt *popt, bool quiet)
 	return true;
 }
 
-
+/*
+ * printPsetInfo: print the state of the "param" formatting parameter in popt.
+ */
 static bool
-printPsetInfo(const char *param, struct printQueryOpt *popt)
+printPsetInfo(const char *param, printQueryOpt *popt)
 {
 	Assert(param != NULL);
 
@@ -4292,6 +4309,77 @@ printPsetInfo(const char *param, struct printQueryOpt *popt)
 	return true;
 }
 
+/*
+ * savePsetInfo: make a malloc'd copy of the data in *popt.
+ *
+ * Possibly this should be somewhere else, but it's a bit specific to psql.
+ */
+printQueryOpt *
+savePsetInfo(const printQueryOpt *popt)
+{
+	printQueryOpt *save;
+
+	save = (printQueryOpt *) pg_malloc(sizeof(printQueryOpt));
+
+	/* Flat-copy all the scalar fields, then duplicate sub-structures. */
+	memcpy(save, popt, sizeof(printQueryOpt));
+
+	/* topt.line_style points to const data that need not be duplicated */
+	if (popt->topt.fieldSep.separator)
+		save->topt.fieldSep.separator = pg_strdup(popt->topt.fieldSep.separator);
+	if (popt->topt.recordSep.separator)
+		save->topt.recordSep.separator = pg_strdup(popt->topt.recordSep.separator);
+	if (popt->topt.tableAttr)
+		save->topt.tableAttr = pg_strdup(popt->topt.tableAttr);
+	if (popt->nullPrint)
+		save->nullPrint = pg_strdup(popt->nullPrint);
+	if (popt->title)
+		save->title = pg_strdup(popt->title);
+
+	/*
+	 * footers and translate_columns are never set in psql's print settings,
+	 * so we needn't write code to duplicate them.
+	 */
+	Assert(popt->footers == NULL);
+	Assert(popt->translate_columns == NULL);
+
+	return save;
+}
+
+/*
+ * restorePsetInfo: restore *popt from the previously-saved copy *save,
+ * then free *save.
+ */
+void
+restorePsetInfo(printQueryOpt *popt, printQueryOpt *save)
+{
+	/* Free all the old data we're about to overwrite the pointers to. */
+
+	/* topt.line_style points to const data that need not be duplicated */
+	if (popt->topt.fieldSep.separator)
+		free(popt->topt.fieldSep.separator);
+	if (popt->topt.recordSep.separator)
+		free(popt->topt.recordSep.separator);
+	if (popt->topt.tableAttr)
+		free(popt->topt.tableAttr);
+	if (popt->nullPrint)
+		free(popt->nullPrint);
+	if (popt->title)
+		free(popt->title);
+
+	/*
+	 * footers and translate_columns are never set in psql's print settings,
+	 * so we needn't write code to duplicate them.
+	 */
+	Assert(popt->footers == NULL);
+	Assert(popt->translate_columns == NULL);
+
+	/* Now we may flat-copy all the fields, including pointers. */
+	memcpy(popt, save, sizeof(printQueryOpt));
+
+	/* Lastly, free "save" ... but its sub-structures now belong to popt. */
+	free(save);
+}
 
 static const char *
 pset_bool_string(bool val)
@@ -4339,7 +4427,7 @@ pset_quoted_string(const char *str)
  * output that produces the correct setting when fed back into \pset.
  */
 static char *
-pset_value_string(const char *param, struct printQueryOpt *popt)
+pset_value_string(const char *param, printQueryOpt *popt)
 {
 	Assert(param != NULL);
 
diff --git a/src/bin/psql/command.h b/src/bin/psql/command.h
index 6113838..006832f 100644
--- a/src/bin/psql/command.h
+++ b/src/bin/psql/command.h
@@ -36,6 +36,10 @@ extern bool do_pset(const char *param,
 					printQueryOpt *popt,
 					bool quiet);
 
+extern printQueryOpt *savePsetInfo(const printQueryOpt *popt);
+
+extern void restorePsetInfo(printQueryOpt *popt, printQueryOpt *save);
+
 extern void connection_warnings(bool in_startup);
 
 extern void SyncVariables(void);
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 396a400..621a33f 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -707,13 +707,8 @@ PrintNotifications(void)
 static bool
 PrintQueryTuples(const PGresult *results)
 {
-	printQueryOpt my_popt = pset.popt;
 	bool result = true;
 
-	/* one-shot expanded output requested via \gx */
-	if (pset.g_expanded)
-		my_popt.topt.expanded = 1;
-
 	/* write output to \g argument, if any */
 	if (pset.gfname)
 	{
@@ -725,7 +720,7 @@ PrintQueryTuples(const PGresult *results)
 		if (is_pipe)
 			disable_sigpipe_trap();
 
-		printQuery(results, &my_popt, fout, false, pset.logfile);
+		printQuery(results, &pset.popt, fout, false, pset.logfile);
 		if (ferror(fout))
 		{
 			pg_log_error("could not print result table: %m");
@@ -742,7 +737,7 @@ PrintQueryTuples(const PGresult *results)
 	}
 	else
 	{
-		printQuery(results, &my_popt, pset.queryFout, false, pset.logfile);
+		printQuery(results, &pset.popt, pset.queryFout, false, pset.logfile);
 		if (ferror(pset.queryFout))
 		{
 			pg_log_error("could not print result table: %m");
@@ -1418,8 +1413,12 @@ sendquery_cleanup:
 		pset.gfname = NULL;
 	}
 
-	/* reset \gx's expanded-mode flag */
-	pset.g_expanded = false;
+	/* restore print settings if \g changed them */
+	if (pset.gsavepopt)
+	{
+		restorePsetInfo(&pset.popt, pset.gsavepopt);
+		pset.gsavepopt = NULL;
+	}
 
 	/* reset \gset trigger */
 	if (pset.gset_prefix)
@@ -1646,10 +1645,6 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 			 "FETCH FORWARD %d FROM _psql_cursor",
 			 fetch_count);
 
-	/* one-shot expanded output requested via \gx */
-	if (pset.g_expanded)
-		my_popt.topt.expanded = 1;
-
 	/* prepare to write output to \g argument, if any */
 	if (pset.gfname)
 	{
diff --git a/src/bin/psql/settings.h b/src/bin/psql/settings.h
index 2b384a3..97941aa 100644
--- a/src/bin/psql/settings.h
+++ b/src/bin/psql/settings.h
@@ -88,10 +88,11 @@ typedef struct _psqlSettings
 
 	PGresult   *last_error_result;	/* most recent error result, if any */
 
-	printQueryOpt popt;
+	printQueryOpt popt;			/* The active print format settings */
 
 	char	   *gfname;			/* one-shot file output argument for \g */
-	bool		g_expanded;		/* one-shot expanded output requested via \gx */
+	printQueryOpt *gsavepopt;	/* if not null, saved print format settings */
+
 	char	   *gset_prefix;	/* one-shot prefix argument for \gset */
 	bool		gdesc_flag;		/* one-shot request to describe query results */
 	bool		gexec_flag;		/* one-shot request to execute query results */
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 1055af5..933e181 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -86,6 +86,10 @@ static backslashResult exec_command_errverbose(PsqlScanState scan_state, bool ac
 static backslashResult exec_command_f(PsqlScanState scan_state, bool active_branch);
 static backslashResult exec_command_g(PsqlScanState scan_state, bool active_branch,
 									  const char *cmd);
+static backslashResult process_command_g_options(char *first_option,
+												 PsqlScanState scan_state,
+												 bool active_branch,
+												 const char *cmd);
 static backslashResult exec_command_gdesc(PsqlScanState scan_state, bool active_branch);
 static backslashResult exec_command_gexec(PsqlScanState scan_state, bool active_branch);
 static backslashResult exec_command_gset(PsqlScanState scan_state, bool active_branch);
@@ -1280,19 +1284,40 @@ exec_command_f(PsqlScanState scan_state, bool active_branch)
 }
 
 /*
- * \g [filename] -- send query, optionally with output to file/pipe
- * \gx [filename] -- same as \g, with expanded mode forced
+ * \g  [(pset-option[=pset-value] ...)] [filename/shell-command]
+ * \gx [(pset-option[=pset-value] ...)] [filename/shell-command]
+ *
+ * Send the current query.  If pset options are specified, they are made
+ * active just for this query.  If a filename or pipe command is given,
+ * the query output goes there.  \gx implicitly forces expanded = 1 along
+ * with any other pset options that are specified.
  */
 static backslashResult
 exec_command_g(PsqlScanState scan_state, bool active_branch, const char *cmd)
 {
 	backslashResult status = PSQL_CMD_SKIP_LINE;
+	char	   *fname;
 
-	if (active_branch)
+	/*
+	 * Because the option processing for this is fairly complicated, we do it
+	 * and then decide whether the branch is active.
+	 */
+	fname = psql_scan_slash_option(scan_state,
+								   OT_FILEPIPE, NULL, false);
+
+	if (fname && fname[0] == '(')
 	{
-		char	   *fname = psql_scan_slash_option(scan_state,
-												   OT_FILEPIPE, NULL, false);
+		/* Consume pset options through trailing ')' ... */
+		status = process_command_g_options(fname + 1, scan_state,
+										   active_branch, cmd);
+		free(fname);
+		/* ... and again attempt to scan the filename. */
+		fname = psql_scan_slash_option(scan_state,
+									   OT_FILEPIPE, NULL, false);
+	}
 
+	if (status == PSQL_CMD_SKIP_LINE && active_branch)
+	{
 		if (!fname)
 			pset.gfname = NULL;
 		else
@@ -1300,22 +1325,89 @@ exec_command_g(PsqlScanState scan_state, bool active_branch, const char *cmd)
 			expand_tilde(&fname);
 			pset.gfname = pg_strdup(fname);
 		}
-		free(fname);
 		if (strcmp(cmd, "gx") == 0)
 		{
-			/* save settings, then force expanded = 1 */
-			pset.gsavepopt = savePsetInfo(&pset.popt);
+			/* save settings if not done already, then force expanded = 1 */
+			if (pset.gsavepopt == NULL)
+				pset.gsavepopt = savePsetInfo(&pset.popt);
 			pset.popt.topt.expanded = 1;
 		}
 		status = PSQL_CMD_SEND;
 	}
-	else
-		ignore_slash_filepipe(scan_state);
+
+	free(fname);
 
 	return status;
 }
 
 /*
+ * Process parenthesized pset options for \g
+ */
+static backslashResult
+process_command_g_options(char *first_option, PsqlScanState scan_state,
+						  bool active_branch, const char *cmd)
+{
+	bool		success = true;
+	bool		found_r_paren = false;
+
+	do
+	{
+		char	   *option;
+		size_t		optlen;
+
+		/* If not first time through, collect a new option */
+		if (first_option)
+			option = first_option;
+		else
+		{
+			option = psql_scan_slash_option(scan_state,
+											OT_NORMAL, NULL, false);
+			if (!option)
+			{
+				if (active_branch)
+				{
+					pg_log_error("\\%s: missing right parenthesis", cmd);
+					success = false;
+				}
+				break;
+			}
+		}
+
+		/* Check for terminating right paren, and remove it from string */
+		optlen = strlen(option);
+		if (optlen > 0 && option[optlen - 1] == ')')
+		{
+			option[--optlen] = '\0';
+			found_r_paren = true;
+		}
+
+		/* If there was anything besides right paren, parse/execute it */
+		if (optlen > 0)
+		{
+			char	   *valptr = strchr(option, '=');
+
+			if (valptr)
+				*valptr++ = '\0';
+			if (active_branch)
+			{
+				/* save settings if not done already, then apply option */
+				if (pset.gsavepopt == NULL)
+					pset.gsavepopt = savePsetInfo(&pset.popt);
+				success &= do_pset(option, valptr, &pset.popt, true);
+			}
+		}
+
+		/* Clean up after this option.  We should not free first_option. */
+		if (first_option)
+			first_option = NULL;
+		else
+			free(option);
+	} while (!found_r_paren);
+
+	return success ? PSQL_CMD_SKIP_LINE : PSQL_CMD_ERROR;
+}
+
+/*
  * \gdesc -- describe query result
  */
 static backslashResult

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