Index: head/bin/sh/builtins.def
===================================================================
--- head/bin/sh/builtins.def
+++ head/bin/sh/builtins.def
@@ -41,6 +41,9 @@
 # without job control.
 # The -h flag specifies that this command is to be excluded from systems
 # based on the NO_HISTORY compile-time symbol.
+# The -n flag specifies that this command can safely be run in the same
+# process when it is the only command in a command substitution.  Some
+# commands have special logic defined in safe_builtin().
 # The -s flag specifies that this is a POSIX 'special built-in' command.
 # The rest of the line specifies the command name or names used to run the
 # command.  The entry for bltincmd, which is run when the user does not specify
@@ -48,43 +51,43 @@
 #
 # NOTE: bltincmd must come first!
 
-bltincmd	builtin
+bltincmd -n	builtin
 aliascmd	alias
 bgcmd -j	bg
 bindcmd		bind
 breakcmd	-s break -s continue
 cdcmd		cd chdir
-commandcmd	command
+commandcmd -n	command
 dotcmd		-s .
-echocmd		echo
+echocmd -n	echo
 evalcmd		-s eval
 execcmd		-s exec
 exitcmd		-s exit
 letcmd		let
 exportcmd	-s export -s readonly
 #exprcmd		expr
-falsecmd	false
+falsecmd -n	false
 fgcmd -j	fg
 freebsd_wordexpcmd	freebsd_wordexp
 getoptscmd	getopts
 hashcmd		hash
 histcmd -h	fc
-jobidcmd	jobid
-jobscmd		jobs
-killcmd		kill
+jobidcmd -n	jobid
+jobscmd -n	jobs
+killcmd -n	kill
 localcmd	local
-printfcmd	printf
-pwdcmd		pwd
+printfcmd -n	printf
+pwdcmd -n	pwd
 readcmd		read
 returncmd	-s return
 setcmd		-s set
 setvarcmd	setvar
 shiftcmd	-s shift
-testcmd		test [
-timescmd	-s times
+testcmd -n	test [
+timescmd -n	-s times
 trapcmd		-s trap
-truecmd		-s : true
-typecmd		type
+truecmd -n	-s : true
+typecmd -n	type
 ulimitcmd	ulimit
 umaskcmd	umask
 unaliascmd	unalias
Index: head/bin/sh/eval.c
===================================================================
--- head/bin/sh/eval.c
+++ head/bin/sh/eval.c
@@ -800,11 +800,8 @@
 static int
 safe_builtin(int idx, int argc, char **argv)
 {
-	if (idx == BLTINCMD || idx == COMMANDCMD || idx == ECHOCMD ||
-	    idx == FALSECMD || idx == JOBIDCMD || idx == JOBSCMD ||
-	    idx == KILLCMD || idx == PRINTFCMD || idx == PWDCMD ||
-	    idx == TESTCMD || idx == TIMESCMD || idx == TRUECMD ||
-	    idx == TYPECMD)
+	/* Generated from builtins.def. */
+	if (safe_builtin_always(idx))
 		return (1);
 	if (idx == EXPORTCMD || idx == TRAPCMD || idx == ULIMITCMD ||
 	    idx == UMASKCMD)
Index: head/bin/sh/mkbuiltins
===================================================================
--- head/bin/sh/mkbuiltins
+++ head/bin/sh/mkbuiltins
@@ -66,6 +66,9 @@
 awk '{	for (i = 2 ; i <= NF ; i++) {
 		if ($i == "-s") {
 			spc = 1;
+		} else if ($i == "-n") {
+			# Handled later for builtins.h
+			continue
 		} else {
 			printf "\t\"\\%03o\\%03o%s\"\n", length($i), (spc ? 128 : 0) + NR-1, $i
 			spc = 0;
@@ -90,4 +93,45 @@
 extern const unsigned char builtincmd[];
 '
 awk '{	printf "int %s(int, char **);\n", $1}' $temp
+
+# Build safe_builtin_always()
+cat <<EOF
+
+static inline int
+safe_builtin_always(int idx)
+{
+EOF
+awk '
+BEGIN { printed = 0 }
+{
+	for (i = 2 ; i <= NF ; i++) {
+		if ($i == "-s") {
+			continue
+		} else if ($i == "-n") {
+			nofork = 1;
+		} else {
+			if (nofork == 0) {
+				continue
+			}
+			if (printed == 1) {
+				printf " || \n\t    "
+			} else {
+				printf "\tif ("
+			}
+			printf "idx == " toupper($1)
+			printed = 1
+			nofork = 0;
+			# Only need to check each once
+			break
+		}
+	}
+}' $temp
+
+cat << EOF
+)
+		return (1);
+	return(0);
+}
+EOF
+
 rm -f $temp