setsid: add optional -f to force fork()

setsid.1

@@ -1,4 +1,4 @@
-.Dd 2015-10-08
+.Dd 2020-07-14
 .Dt SETSID 1
 .Os sbase
 .Sh NAME
@@ -6,6 +6,7 @@
 .Nd run a command in a new session
 .Sh SYNOPSIS
 .Nm
+.Op Fl f
 .Ar cmd
 .Op Ar arg ...
 .Sh DESCRIPTION

setsid.c

@@ -4,10 +4,12 @@
 
 #include "util.h"
 
+static int fflag = 0;
+
 static void
 usage(void)
 {
-	eprintf("usage: %s cmd [arg ...]\n", argv0);
+	eprintf("usage: %s cmd [-f] [arg ...]\n", argv0);
 }
 
 int
@@ -16,6 +18,9 @@ main(int argc, char *argv[])
 	int savederrno;
 
 	ARGBEGIN {
+	case 'f':
+		fflag = 1;
+		break;
 	default:
 		usage();
 	} ARGEND
@@ -23,7 +28,7 @@ main(int argc, char *argv[])
 	if (!argc)
 		usage();
 
-	if (getpgrp() == getpid()) {
+	if (fflag || getpgrp() == getpid()) {
 		switch (fork()) {
 		case -1:
 			eprintf("fork:");