From 4c565d2020230ad3fdf603fde32b9892e56c16e1 Mon Sep 17 00:00:00 2001
From: David Vazgenovich Shakaryan <dvshakaryan@gmail.com>
Date: Mon, 26 Feb 2024 20:23:19 -0800
Subject: add ability to fork and print PID after locking

---
 slock.1 |  5 +++++
 slock.c | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/slock.1 b/slock.1
index 40c15e1..08b62b9 100644
--- a/slock.1
+++ b/slock.1
@@ -6,6 +6,7 @@
 .Nd simple X screen locker
 .Sh SYNOPSIS
 .Nm
+.Op Fl f Op Fl p
 .Op Fl v
 .Op Ar cmd Op Ar arg ...
 .Sh DESCRIPTION
@@ -17,6 +18,10 @@ is executed after the screen has been locked.
 .Pp
 The options are as follows:
 .Bl -tag -width Ds
+.It Fl f
+Fork and exit parent process after locking screen.
+.It Fl p
+Print child PID to stdout after forking.
 .It Fl v
 Print version information to stdout and exit.
 .El
diff --git a/slock.c b/slock.c
index b2f14e3..0036c10 100644
--- a/slock.c
+++ b/slock.c
@@ -10,6 +10,7 @@
 #include <pwd.h>
 #include <stdarg.h>
 #include <stdlib.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
@@ -300,7 +301,7 @@ lockscreen(Display *dpy, struct xrandr *rr, int screen)
 static void
 usage(void)
 {
-	die("usage: slock [-v] [cmd [arg ...]]\n");
+	die("usage: slock [-f [-p]] [-v] [cmd [arg ...]]\n");
 }
 
 int
@@ -314,8 +315,19 @@ main(int argc, char **argv) {
 	const char *hash;
 	Display *dpy;
 	int s, nlocks, nscreens;
+	int opt_fork, opt_pid;
+	pid_t pid;
+
+	opt_fork = 0;
+	opt_pid = 0;
 
 	ARGBEGIN {
+	case 'f':
+		opt_fork = 1;
+		break;
+	case 'p':
+		opt_pid = 1;
+		break;
 	case 'v':
 		puts("slock-"VERSION);
 		return 0;
@@ -323,6 +335,9 @@ main(int argc, char **argv) {
 		usage();
 	} ARGEND
 
+	if (opt_pid && !opt_fork)
+		usage();
+
 	/* validate drop-user and -group */
 	errno = 0;
 	if (!(pwd = getpwnam(user)))
@@ -374,6 +389,20 @@ main(int argc, char **argv) {
 	if (nlocks != nscreens)
 		return 1;
 
+	if (opt_fork) {
+		switch (pid = fork()) {
+		case -1:
+			die("slock: fork failed: %s\n", strerror(errno));
+		case 0:
+			freopen("/dev/null", "w", stdout);
+			break;
+		default:
+			if (opt_pid)
+				printf("%ji\n", (intmax_t)pid);
+			exit(0);
+		}
+	}
+
 	/* run post-lock command */
 	if (argc > 0) {
 		switch (fork()) {
-- 
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