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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: "David G. Johnston" <david.g.johnston@gmail.com>,
        Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: Set arbitrary GUC options during initdb
In-reply-to: <3337560.1674837348@sss.pgh.pa.us>
References: <2844176.1674681919@sss.pgh.pa.us> <8a8fda29-5a68-ba68-a2ff-8d17602b3762@enterprisedb.com> <3331317.1674833645@sss.pgh.pa.us> <CA+TgmoY4gndkosTZf=Zs1_SfsfO_13c7-yazryweZvLwSTHLgA@mail.gmail.com> <3332912.1674834822@sss.pgh.pa.us> <CAKFQuwauwt+w8HbtU_-Mqo-aZ1Qjsah13E5_iFEUTVpVc1PTAw@mail.gmail.com> <3337560.1674837348@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Fri, 27 Jan 2023 11:35:48 -0500"
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I wrote:
>>> Anyway, it seems like I gotta work harder.  I'll produce a
>>> new patch.

The string-hacking was fully as tedious as I expected.  However, the
output looks pretty nice, and this does have the advantage that the
pre-programmed substitutions become a lot more robust: they are no
longer dependent on the initdb code exactly matching what is in
postgresql.conf.sample.

			regards, tom lane


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diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 5b2bdac101..724188b1b5 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -433,6 +433,23 @@ PostgreSQL documentation
     Other, less commonly used, options are also available:
 =

     <variablelist>
+     <varlistentry id=3D"app-initdb-option-set">
+      <term><option>-c <replaceable>name</replaceable>=3D<replaceable>val=
ue</replaceable></option></term>
+      <term><option>--set <replaceable>name</replaceable>=3D<replaceable>=
value</replaceable></option></term>
+      <listitem>
+       <para>
+        Forcibly set the server parameter <replaceable>name</replaceable>
+        to <replaceable>value</replaceable> during <command>initdb</comma=
nd>,
+        and also install that setting in the
+        generated <filename>postgresql.conf</filename> file,
+        so that it will apply during future server runs.
+        This option can be given more than once to set several parameters=
.
+        It is primarily useful when the environment is such that the serv=
er
+        will not start at all using the default parameters.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id=3D"app-initdb-option-debug">
       <term><option>-d</option></term>
       <term><option>--debug</option></term>
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 7a58c33ace..c955c0837e 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -48,6 +48,7 @@
 =

 #include "postgres_fe.h"
 =

+#include <ctype.h>
 #include <dirent.h>
 #include <fcntl.h>
 #include <netdb.h>
@@ -82,6 +83,13 @@
 /* Ideally this would be in a .h file, but it hardly seems worth the trou=
ble */
 extern const char *select_default_timezone(const char *share_path);
 =

+/* simple list of strings */
+typedef struct _stringlist
+{
+	char	   *str;
+	struct _stringlist *next;
+} _stringlist;
+
 static const char *const auth_methods_host[] =3D {
 	"trust", "reject", "scram-sha-256", "md5", "password", "ident", "radius"=
,
 #ifdef ENABLE_GSS
@@ -142,6 +150,8 @@ static char *pwfilename =3D NULL;
 static char *superuser_password =3D NULL;
 static const char *authmethodhost =3D NULL;
 static const char *authmethodlocal =3D NULL;
+static _stringlist *extra_guc_names =3D NULL;
+static _stringlist *extra_guc_values =3D NULL;
 static bool debug =3D false;
 static bool noclean =3D false;
 static bool noinstructions =3D false;
@@ -242,7 +252,10 @@ static char backend_exec[MAXPGPATH];
 =

 static char **replace_token(char **lines,
 							const char *token, const char *replacement);
-
+static char **replace_guc_value(char **lines,
+								const char *guc_name, const char *guc_value,
+								bool mark_as_comment);
+static bool guc_value_requires_quotes(const char *guc_value);
 static char **readfile(const char *path);
 static void writefile(char *path, char **lines);
 static FILE *popen_check(const char *command, const char *mode);
@@ -253,6 +266,7 @@ static void check_input(char *path);
 static void write_version_file(const char *extrapath);
 static void set_null_conf(void);
 static void test_config_settings(void);
+static bool test_specific_config_settings(int test_conns, int test_buffs)=
;
 static void setup_config(void);
 static void bootstrap_template1(void);
 static void setup_auth(FILE *cmdfd);
@@ -360,9 +374,34 @@ escape_quotes_bki(const char *src)
 }
 =

 /*
- * make a copy of the array of lines, with token replaced by replacement
+ * Add an item at the end of a stringlist.
+ */
+static void
+add_stringlist_item(_stringlist **listhead, const char *str)
+{
+	_stringlist *newentry =3D pg_malloc(sizeof(_stringlist));
+	_stringlist *oldentry;
+
+	newentry->str =3D pg_strdup(str);
+	newentry->next =3D NULL;
+	if (*listhead =3D=3D NULL)
+		*listhead =3D newentry;
+	else
+	{
+		for (oldentry =3D *listhead; oldentry->next; oldentry =3D oldentry->nex=
t)
+			 /* skip */ ;
+		oldentry->next =3D newentry;
+	}
+}
+
+/*
+ * Make a copy of the array of lines, with token replaced by replacement
  * the first time it occurs on each line.
  *
+ * The original data structure is not changed, but we share any unchanged
+ * strings with it.  (This definition lends itself to memory leaks, but
+ * we don't care too much about leaks in this program.)
+ *
  * This does most of what sed was used for in the shell script, but
  * doesn't need any regexp stuff.
  */
@@ -416,6 +455,168 @@ replace_token(char **lines, const char *token, const=
 char *replacement)
 	return result;
 }
 =

+/*
+ * Make a copy of the array of lines, replacing the possibly-commented-ou=
t
+ * assignment of parameter guc_name with a live assignment of guc_value.
+ * The value will be suitably quoted.
+ *
+ * If mark_as_comment is true, the replacement line is prefixed with '#'.
+ * This is used for fixing up cases where the effective default might not
+ * match what is in postgresql.conf.sample.
+ *
+ * We assume there's at most one matching assignment.  If we find no matc=
h,
+ * append a new line with the desired assignment.
+ *
+ * The original data structure is not changed, but we share any unchanged
+ * strings with it.  (This definition lends itself to memory leaks, but
+ * we don't care too much about leaks in this program.)
+ */
+static char **
+replace_guc_value(char **lines, const char *guc_name, const char *guc_val=
ue,
+				  bool mark_as_comment)
+{
+	char	  **result;
+	int			namelen =3D strlen(guc_name);
+	PQExpBuffer newline =3D createPQExpBuffer();
+	int			numlines =3D 0;
+	int			i;
+
+	/* prepare the replacement line, except for possible comment and newline=
 */
+	if (mark_as_comment)
+		appendPQExpBufferChar(newline, '#');
+	appendPQExpBuffer(newline, "%s =3D ", guc_name);
+	if (guc_value_requires_quotes(guc_value))
+		appendPQExpBuffer(newline, "'%s'", escape_quotes(guc_value));
+	else
+		appendPQExpBufferStr(newline, guc_value);
+
+	/* create the new pointer array */
+	for (i =3D 0; lines[i]; i++)
+		numlines++;
+
+	/* leave room for one extra string in case we need to append */
+	result =3D (char **) pg_malloc((numlines + 2) * sizeof(char *));
+
+	/* initialize result with all the same strings */
+	memcpy(result, lines, (numlines + 1) * sizeof(char *));
+
+	for (i =3D 0; i < numlines; i++)
+	{
+		const char *where;
+
+		/*
+		 * Look for a line assigning to guc_name.  Typically it will be
+		 * preceded by '#', but that might not be the case if a -c switch
+		 * overrides a previous assignment.  We allow leading whitespace too,
+		 * although normally there wouldn't be any.
+		 */
+		where =3D result[i];
+		while (*where =3D=3D '#' || isspace((unsigned char) *where))
+			where++;
+		if (strncmp(where, guc_name, namelen) !=3D 0)
+			continue;
+		where +=3D namelen;
+		while (isspace((unsigned char) *where))
+			where++;
+		if (*where !=3D '=3D')
+			continue;
+
+		/* found it -- append the original comment if any */
+		where =3D strrchr(where, '#');
+		if (where)
+		{
+			/*
+			 * We try to preserve original indentation, which is tedious.
+			 * oldindent and newindent are measured in de-tab-ified columns.
+			 */
+			const char *ptr;
+			int			oldindent =3D 0;
+			int			newindent;
+
+			for (ptr =3D result[i]; ptr < where; ptr++)
+			{
+				if (*ptr =3D=3D '\t')
+					oldindent +=3D 8 - (oldindent % 8);
+				else
+					oldindent++;
+			}
+			/* ignore the possibility of tabs in guc_value */
+			newindent =3D newline->len;
+			/* append appropriate tabs and spaces, forcing at least one */
+			oldindent =3D Max(oldindent, newindent + 1);
+			while (newindent < oldindent)
+			{
+				int			newindent_if_tab =3D newindent + 8 - (newindent % 8);
+
+				if (newindent_if_tab <=3D oldindent)
+				{
+					appendPQExpBufferChar(newline, '\t');
+					newindent =3D newindent_if_tab;
+				}
+				else
+				{
+					appendPQExpBufferChar(newline, ' ');
+					newindent++;
+				}
+			}
+			/* and finally append the old comment */
+			appendPQExpBufferStr(newline, where);
+			/* we'll have appended the original newline; don't add another */
+		}
+		else
+			appendPQExpBufferChar(newline, '\n');
+
+		result[i] =3D newline->data;
+
+		break;					/* assume there's only one match */
+	}
+
+	if (i >=3D numlines)
+	{
+		/*
+		 * No match, so append a new entry.  (We rely on the bootstrap server
+		 * to complain if it's not a valid GUC name.)
+		 */
+		appendPQExpBufferChar(newline, '\n');
+		result[numlines++] =3D newline->data;
+		result[numlines] =3D NULL;	/* keep the array null-terminated */
+	}
+
+	return result;
+}
+
+/*
+ * Decide if we should quote a replacement GUC value.  We aren't too tens=
e
+ * here, but we'd like to avoid quoting simple identifiers and numbers
+ * with units, which are common cases.
+ */
+static bool
+guc_value_requires_quotes(const char *guc_value)
+{
+	/* Don't use <ctype.h> macros here, they might accept too much */
+#define LETTERS	"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+#define DIGITS	"0123456789"
+
+	if (*guc_value =3D=3D '\0')
+		return true;			/* empty string must be quoted */
+	if (strchr(LETTERS, *guc_value))
+	{
+		if (strspn(guc_value, LETTERS DIGITS) =3D=3D strlen(guc_value))
+			return false;		/* it's an identifier */
+		return true;			/* nope */
+	}
+	if (strchr(DIGITS, *guc_value))
+	{
+		/* skip over digits */
+		guc_value +=3D strspn(guc_value, DIGITS);
+		/* there can be zero or more unit letters after the digits */
+		if (strspn(guc_value, LETTERS) =3D=3D strlen(guc_value))
+			return false;		/* it's a number, possibly with units */
+		return true;			/* nope */
+	}
+	return true;				/* all else must be quoted */
+}
+
 /*
  * get the lines from a text file
  */
@@ -873,11 +1074,9 @@ test_config_settings(void)
 		400, 300, 200, 100, 50
 	};
 =

-	char		cmd[MAXPGPATH];
 	const int	connslen =3D sizeof(trial_conns) / sizeof(int);
 	const int	bufslen =3D sizeof(trial_bufs) / sizeof(int);
 	int			i,
-				status,
 				test_conns,
 				test_buffs,
 				ok_buffers =3D 0;
@@ -903,19 +1102,7 @@ test_config_settings(void)
 		test_conns =3D trial_conns[i];
 		test_buffs =3D MIN_BUFS_FOR_CONNS(test_conns);
 =

-		snprintf(cmd, sizeof(cmd),
-				 "\"%s\" --check %s %s "
-				 "-c max_connections=3D%d "
-				 "-c shared_buffers=3D%d "
-				 "-c dynamic_shared_memory_type=3D%s "
-				 "< \"%s\" > \"%s\" 2>&1",
-				 backend_exec, boot_options, extra_options,
-				 test_conns, test_buffs,
-				 dynamic_shared_memory_type,
-				 DEVNULL, DEVNULL);
-		fflush(NULL);
-		status =3D system(cmd);
-		if (status =3D=3D 0)
+		if (test_specific_config_settings(test_conns, test_buffs))
 		{
 			ok_buffers =3D test_buffs;
 			break;
@@ -940,19 +1127,7 @@ test_config_settings(void)
 			break;
 		}
 =

-		snprintf(cmd, sizeof(cmd),
-				 "\"%s\" --check %s %s "
-				 "-c max_connections=3D%d "
-				 "-c shared_buffers=3D%d "
-				 "-c dynamic_shared_memory_type=3D%s "
-				 "< \"%s\" > \"%s\" 2>&1",
-				 backend_exec, boot_options, extra_options,
-				 n_connections, test_buffs,
-				 dynamic_shared_memory_type,
-				 DEVNULL, DEVNULL);
-		fflush(NULL);
-		status =3D system(cmd);
-		if (status =3D=3D 0)
+		if (test_specific_config_settings(n_connections, test_buffs))
 			break;
 	}
 	n_buffers =3D test_buffs;
@@ -968,6 +1143,48 @@ test_config_settings(void)
 	printf("%s\n", default_timezone ? default_timezone : "GMT");
 }
 =

+/*
+ * Test a specific combination of configuration settings.
+ */
+static bool
+test_specific_config_settings(int test_conns, int test_buffs)
+{
+	PQExpBuffer cmd =3D createPQExpBuffer();
+	_stringlist *gnames,
+			   *gvalues;
+	int			status;
+
+	/* Set up the test postmaster invocation */
+	printfPQExpBuffer(cmd,
+					  "\"%s\" --check %s %s "
+					  "-c max_connections=3D%d "
+					  "-c shared_buffers=3D%d "
+					  "-c dynamic_shared_memory_type=3D%s",
+					  backend_exec, boot_options, extra_options,
+					  test_conns, test_buffs,
+					  dynamic_shared_memory_type);
+
+	/* Add any user-given setting overrides */
+	for (gnames =3D extra_guc_names, gvalues =3D extra_guc_values;
+		 gnames !=3D NULL;		/* assume lists have the same length */
+		 gnames =3D gnames->next, gvalues =3D gvalues->next)
+	{
+		appendPQExpBuffer(cmd, " -c %s=3D", gnames->str);
+		appendShellString(cmd, gvalues->str);
+	}
+
+	appendPQExpBuffer(cmd,
+					  " < \"%s\" > \"%s\" 2>&1",
+					  DEVNULL, DEVNULL);
+
+	fflush(NULL);
+	status =3D system(cmd->data);
+
+	destroyPQExpBuffer(cmd);
+
+	return (status =3D=3D 0);
+}
+
 /*
  * Calculate the default wal_size with a "pretty" unit.
  */
@@ -995,6 +1212,8 @@ setup_config(void)
 	char		repltok[MAXPGPATH];
 	char		path[MAXPGPATH];
 	char	   *autoconflines[3];
+	_stringlist *gnames,
+			   *gvalues;
 =

 	fputs(_("creating configuration files ... "), stdout);
 	fflush(stdout);
@@ -1003,120 +1222,106 @@ setup_config(void)
 =

 	conflines =3D readfile(conf_file);
 =

-	snprintf(repltok, sizeof(repltok), "max_connections =3D %d", n_connectio=
ns);
-	conflines =3D replace_token(conflines, "#max_connections =3D 100", replt=
ok);
+	snprintf(repltok, sizeof(repltok), "%d", n_connections);
+	conflines =3D replace_guc_value(conflines, "max_connections",
+								  repltok, false);
 =

 	if ((n_buffers * (BLCKSZ / 1024)) % 1024 =3D=3D 0)
-		snprintf(repltok, sizeof(repltok), "shared_buffers =3D %dMB",
+		snprintf(repltok, sizeof(repltok), "%dMB",
 				 (n_buffers * (BLCKSZ / 1024)) / 1024);
 	else
-		snprintf(repltok, sizeof(repltok), "shared_buffers =3D %dkB",
+		snprintf(repltok, sizeof(repltok), "%dkB",
 				 n_buffers * (BLCKSZ / 1024));
-	conflines =3D replace_token(conflines, "#shared_buffers =3D 128MB", repl=
tok);
+	conflines =3D replace_guc_value(conflines, "shared_buffers",
+								  repltok, false);
 =

-	snprintf(repltok, sizeof(repltok), "#unix_socket_directories =3D '%s'",
-			 DEFAULT_PGSOCKET_DIR);
-	conflines =3D replace_token(conflines, "#unix_socket_directories =3D '/t=
mp'",
-							  repltok);
+	conflines =3D replace_guc_value(conflines, "lc_messages", lc_messages, f=
alse);
 =

-#if DEF_PGPORT !=3D 5432
-	snprintf(repltok, sizeof(repltok), "#port =3D %d", DEF_PGPORT);
-	conflines =3D replace_token(conflines, "#port =3D 5432", repltok);
-#endif
+	conflines =3D replace_guc_value(conflines, "lc_monetary", lc_monetary, f=
alse);
 =

-	/* set default max_wal_size and min_wal_size */
-	snprintf(repltok, sizeof(repltok), "min_wal_size =3D %s",
-			 pretty_wal_size(DEFAULT_MIN_WAL_SEGS));
-	conflines =3D replace_token(conflines, "#min_wal_size =3D 80MB", repltok=
);
+	conflines =3D replace_guc_value(conflines, "lc_numeric", lc_numeric, fal=
se);
 =

-	snprintf(repltok, sizeof(repltok), "max_wal_size =3D %s",
-			 pretty_wal_size(DEFAULT_MAX_WAL_SEGS));
-	conflines =3D replace_token(conflines, "#max_wal_size =3D 1GB", repltok)=
;
-
-	snprintf(repltok, sizeof(repltok), "lc_messages =3D '%s'",
-			 escape_quotes(lc_messages));
-	conflines =3D replace_token(conflines, "#lc_messages =3D 'C'", repltok);
-
-	snprintf(repltok, sizeof(repltok), "lc_monetary =3D '%s'",
-			 escape_quotes(lc_monetary));
-	conflines =3D replace_token(conflines, "#lc_monetary =3D 'C'", repltok);
-
-	snprintf(repltok, sizeof(repltok), "lc_numeric =3D '%s'",
-			 escape_quotes(lc_numeric));
-	conflines =3D replace_token(conflines, "#lc_numeric =3D 'C'", repltok);
-
-	snprintf(repltok, sizeof(repltok), "lc_time =3D '%s'",
-			 escape_quotes(lc_time));
-	conflines =3D replace_token(conflines, "#lc_time =3D 'C'", repltok);
+	conflines =3D replace_guc_value(conflines, "lc_time", lc_time, false);
 =

 	switch (locale_date_order(lc_time))
 	{
 		case DATEORDER_YMD:
-			strcpy(repltok, "datestyle =3D 'iso, ymd'");
+			strcpy(repltok, "iso, ymd");
 			break;
 		case DATEORDER_DMY:
-			strcpy(repltok, "datestyle =3D 'iso, dmy'");
+			strcpy(repltok, "iso, dmy");
 			break;
 		case DATEORDER_MDY:
 		default:
-			strcpy(repltok, "datestyle =3D 'iso, mdy'");
+			strcpy(repltok, "iso, mdy");
 			break;
 	}
-	conflines =3D replace_token(conflines, "#datestyle =3D 'iso, mdy'", repl=
tok);
+	conflines =3D replace_guc_value(conflines, "datestyle", repltok, false);
 =

 	snprintf(repltok, sizeof(repltok),
-			 "default_text_search_config =3D 'pg_catalog.%s'",
-			 escape_quotes(default_text_search_config));
-	conflines =3D replace_token(conflines,
-							  "#default_text_search_config =3D 'pg_catalog.simple'",
-							  repltok);
+			 "pg_catalog.%s", default_text_search_config);
+	conflines =3D replace_guc_value(conflines, "default_text_search_config",
+								  repltok, false);
 =

 	if (default_timezone)
 	{
-		snprintf(repltok, sizeof(repltok), "timezone =3D '%s'",
-				 escape_quotes(default_timezone));
-		conflines =3D replace_token(conflines, "#timezone =3D 'GMT'", repltok);
-		snprintf(repltok, sizeof(repltok), "log_timezone =3D '%s'",
-				 escape_quotes(default_timezone));
-		conflines =3D replace_token(conflines, "#log_timezone =3D 'GMT'", replt=
ok);
+		conflines =3D replace_guc_value(conflines, "timezone",
+									  default_timezone, false);
+		conflines =3D replace_guc_value(conflines, "log_timezone",
+									  default_timezone, false);
 	}
 =

-	snprintf(repltok, sizeof(repltok), "dynamic_shared_memory_type =3D %s",
-			 dynamic_shared_memory_type);
-	conflines =3D replace_token(conflines, "#dynamic_shared_memory_type =3D =
posix",
-							  repltok);
+	conflines =3D replace_guc_value(conflines, "dynamic_shared_memory_type",
+								  dynamic_shared_memory_type, false);
+
+	/*
+	 * Fix up various entries to match the true compile-time defaults.  Sinc=
e
+	 * these are indeed defaults, keep the postgresql.conf lines commented.
+	 */
+	conflines =3D replace_guc_value(conflines, "unix_socket_directories",
+								  DEFAULT_PGSOCKET_DIR, true);
+
+#if DEF_PGPORT !=3D 5432
+	snprintf(repltok, sizeof(repltok), "%d", DEF_PGPORT);
+	conflines =3D replace_guc_value(conflines, "port",
+								  repltok, true);
+#endif
+
+	conflines =3D replace_guc_value(conflines, "min_wal_size",
+								  pretty_wal_size(DEFAULT_MIN_WAL_SEGS), true);
+
+	conflines =3D replace_guc_value(conflines, "max_wal_size",
+								  pretty_wal_size(DEFAULT_MAX_WAL_SEGS), true);
 =

 #if DEFAULT_BACKEND_FLUSH_AFTER > 0
-	snprintf(repltok, sizeof(repltok), "#backend_flush_after =3D %dkB",
+	snprintf(repltok, sizeof(repltok), "%dkB",
 			 DEFAULT_BACKEND_FLUSH_AFTER * (BLCKSZ / 1024));
-	conflines =3D replace_token(conflines, "#backend_flush_after =3D 0",
-							  repltok);
+	conflines =3D replace_guc_value(conflines, "backend_flush_after",
+								  repltok, true);
 #endif
 =

 #if DEFAULT_BGWRITER_FLUSH_AFTER > 0
-	snprintf(repltok, sizeof(repltok), "#bgwriter_flush_after =3D %dkB",
+	snprintf(repltok, sizeof(repltok), "%dkB",
 			 DEFAULT_BGWRITER_FLUSH_AFTER * (BLCKSZ / 1024));
-	conflines =3D replace_token(conflines, "#bgwriter_flush_after =3D 0",
-							  repltok);
+	conflines =3D replace_guc_value(conflines, "bgwriter_flush_after",
+								  repltok, true);
 #endif
 =

 #if DEFAULT_CHECKPOINT_FLUSH_AFTER > 0
-	snprintf(repltok, sizeof(repltok), "#checkpoint_flush_after =3D %dkB",
+	snprintf(repltok, sizeof(repltok), "%dkB",
 			 DEFAULT_CHECKPOINT_FLUSH_AFTER * (BLCKSZ / 1024));
-	conflines =3D replace_token(conflines, "#checkpoint_flush_after =3D 0",
-							  repltok);
+	conflines =3D replace_guc_value(conflines, "checkpoint_flush_after",
+								  repltok, true);
 #endif
 =

 #ifndef USE_PREFETCH
-	conflines =3D replace_token(conflines,
-							  "#effective_io_concurrency =3D 1",
-							  "#effective_io_concurrency =3D 0");
+	conflines =3D replace_guc_value(conflines, "effective_io_concurrency",
+								  "0", true);
 #endif
 =

 #ifdef WIN32
-	conflines =3D replace_token(conflines,
-							  "#update_process_title =3D on",
-							  "#update_process_title =3D off");
+	conflines =3D replace_guc_value(conflines, "update_process_title",
+								  "off", true);
 #endif
 =

 	/*
@@ -1128,9 +1333,8 @@ setup_config(void)
 		(strcmp(authmethodhost, "md5") =3D=3D 0 &&
 		 strcmp(authmethodlocal, "scram-sha-256") !=3D 0))
 	{
-		conflines =3D replace_token(conflines,
-								  "#password_encryption =3D scram-sha-256",
-								  "password_encryption =3D md5");
+		conflines =3D replace_guc_value(conflines, "password_encryption",
+									  "md5", false);
 	}
 =

 	/*
@@ -1141,11 +1345,22 @@ setup_config(void)
 	 */
 	if (pg_dir_create_mode =3D=3D PG_DIR_MODE_GROUP)
 	{
-		conflines =3D replace_token(conflines,
-								  "#log_file_mode =3D 0600",
-								  "log_file_mode =3D 0640");
+		conflines =3D replace_guc_value(conflines, "log_file_mode",
+									  "0640", false);
 	}
 =

+	/*
+	 * Now replace anything that's overridden via -c switches.
+	 */
+	for (gnames =3D extra_guc_names, gvalues =3D extra_guc_values;
+		 gnames !=3D NULL;		/* assume lists have the same length */
+		 gnames =3D gnames->next, gvalues =3D gvalues->next)
+	{
+		conflines =3D replace_guc_value(conflines, gnames->str,
+									  gvalues->str, false);
+	}
+
+	/* ... and write out the finished postgresql.conf file */
 	snprintf(path, sizeof(path), "%s/postgresql.conf", pg_data);
 =

 	writefile(path, conflines);
@@ -2124,6 +2339,7 @@ usage(const char *progname)
 	printf(_("  -X, --waldir=3DWALDIR       location for the write-ahead log=
 directory\n"));
 	printf(_("      --wal-segsize=3DSIZE    size of WAL segments, in megabyt=
es\n"));
 	printf(_("\nLess commonly used options:\n"));
+	printf(_("  -c, --set NAME=3DVALUE      override default setting for ser=
ver parameter\n"));
 	printf(_("  -d, --debug               generate lots of debugging output\=
n"));
 	printf(_("      --discard-caches      set debug_discard_caches=3D1\n"));
 	printf(_("  -L DIRECTORY              where to find the input files\n"))=
;
@@ -2759,6 +2975,7 @@ main(int argc, char *argv[])
 		{"nosync", no_argument, NULL, 'N'}, /* for backwards compatibility */
 		{"no-sync", no_argument, NULL, 'N'},
 		{"no-instructions", no_argument, NULL, 13},
+		{"set", required_argument, NULL, 'c'},
 		{"sync-only", no_argument, NULL, 'S'},
 		{"waldir", required_argument, NULL, 'X'},
 		{"wal-segsize", required_argument, NULL, 12},
@@ -2808,7 +3025,8 @@ main(int argc, char *argv[])
 =

 	/* process command-line options */
 =

-	while ((c =3D getopt_long(argc, argv, "A:dD:E:gkL:nNsST:U:WX:", long_opt=
ions, &option_index)) !=3D -1)
+	while ((c =3D getopt_long(argc, argv, "A:c:dD:E:gkL:nNsST:U:WX:",
+							long_options, &option_index)) !=3D -1)
 	{
 		switch (c)
 		{
@@ -2831,6 +3049,24 @@ main(int argc, char *argv[])
 			case 11:
 				authmethodhost =3D pg_strdup(optarg);
 				break;
+			case 'c':
+				{
+					char	   *buf =3D pg_strdup(optarg);
+					char	   *equals =3D strchr(buf, '=3D');
+
+					if (!equals)
+					{
+						pg_log_error("-c %s requires a value", buf);
+						pg_log_error_hint("Try \"%s --help\" for more information.",
+										  progname);
+						exit(1);
+					}
+					*equals++ =3D '\0';	/* terminate variable name */
+					add_stringlist_item(&extra_guc_names, buf);
+					add_stringlist_item(&extra_guc_values, equals);
+					pfree(buf);
+				}
+				break;
 			case 'D':
 				pg_data =3D pg_strdup(optarg);
 				break;
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.=
pl
index 772769acab..1e23ac8d0c 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -48,7 +48,13 @@ mkdir $datadir;
 	local (%ENV) =3D %ENV;
 	delete $ENV{TZ};
 =

-	command_ok([ 'initdb', '-N', '-T', 'german', '-X', $xlogdir, $datadir ],
+	# while we are here, also exercise -T and -c options
+	command_ok(
+		[
+			'initdb', '-N', '-T', 'german', '-c',
+			'default_text_search_config=3Dgerman',
+			'-X', $xlogdir, $datadir
+		],
 		'successful creation');
 =

 	# Permissions on PGDATA should be default
@@ -147,4 +153,7 @@ command_fails(
 	],
 	'fails for invalid option combination');
 =

+command_fails([ 'initdb', '--no-sync', '--set', 'foo=3Dbar', "$tempdir/da=
taX" ],
+	'fails for invalid --set option');
+
 done_testing();

------- =_aaaaaaaaaa0--