Add setsid(1) by arg

Makefile

@@ -68,6 +68,7 @@ SRC = \
 	rm.c       \
 	rmdir.c    \
 	sleep.c    \
+	setsid.c   \
 	sort.c     \
 	split.c    \
 	sponge.c   \

setsid.1

@@ -0,0 +1,7 @@
+.TH SETSID 1 sbase\-VERSION
+.SH NAME
+setsid \- run a program in a new session
+.SH SYNOPSIS
+.B setsid
+.RI program
+.RI [ arg ...]

setsid.c

@@ -0,0 +1,42 @@
+/* (C)opyright MMVI Anselm R. Garbe <garbeam at gmail dot com>
+ * See LICENSE file for license details. */
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s cmd [arg ...]\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND;
+
+	if (argc < 1)
+		usage();
+
+	if(getpgrp() == getpid()) {
+		switch(fork()){
+		case -1:
+			eprintf("fork:");
+		case 0:
+			break;
+		default:
+			exit(0);
+		}
+	}
+	if(setsid() < 0)
+		eprintf("setsid:");
+	execvp(argv[0], argv);
+	eprintf("execvp:");
+	/* NOTREACHED */
+	return 0;
+}