3 files changed, 13 insertions, 8 deletions
diff --git a/common.h b/common.h
index c4de909..996b9ef 100644
--- a/common.h
+++ b/common.h
@@ -112,6 +112,6 @@ struct process *add_process(pid_t pid, unsigned long int trace_options);
 void remove_process(struct process *proc);
 
 /* util.c */
-void set_trace_output(FILE *fp);
+void setup_trace_output(FILE *fp, int multiprocess);
 void tprintf(struct process *proc, const char *fmt, ...);
 _Noreturn void eprintf(const char *fmt, ...);
diff --git a/sctrace.c b/sctrace.c
index 0ab561c..f027a77 100644
--- a/sctrace.c
+++ b/sctrace.c
@@ -99,7 +99,7 @@ main(int argc, char **argv)
 	char *outfile = NULL;
 	FILE *outfp = stderr;
 	const char *num = NULL;
-	int status, exit_value = 0, trace_event, with_argv0 = 0;
+	int status, exit_value = 0, trace_event, with_argv0 = 0, multiprocess = 0;
 	unsigned long int trace_options = PTRACE_O_EXITKILL | PTRACE_O_TRACESYSGOOD | PTRACE_O_TRACEEXEC;
 	struct process *proc, *proc2;
 	unsigned long int event;
@@ -118,6 +118,7 @@ main(int argc, char **argv)
 	case 'f':
 		trace_options |= PTRACE_O_TRACEFORK;
 		trace_options |= PTRACE_O_TRACEVFORK;
+		multiprocess = 1;
 		break;
 	default:
 		usage();
@@ -184,7 +185,7 @@ main(int argc, char **argv)
 	}
 
 have_outfp:
-	set_trace_output(outfp);
+	setup_trace_output(outfp, multiprocess);
 
 	for (;;) {
 		pid = wait(&status);
diff --git a/util.c b/util.c
index 76a8a36..7ee9c51 100644
--- a/util.c
+++ b/util.c
@@ -5,11 +5,13 @@
 static FILE *trace_fp;
 static char last_char = '\n';
 static pid_t last_pid = 0;
+static int multiproctrace;
 
 
 void
-set_trace_output(FILE *fp)
+setup_trace_output(FILE *fp, int multiprocess)
 {
+	multiproctrace = multiprocess;
 	trace_fp = fp;
 }
 
@@ -22,10 +24,12 @@ tprintf(struct process *proc, const char *fmt, ...)
 		last_pid = 0;
 		fmt = &fmt[1];
 	}
-	if (last_char == '\n')
-		fprintf(trace_fp, "[%ju] ", (uintmax_t)proc->pid);
-	else if (proc->pid != last_pid)
-		fprintf(trace_fp, "\n[%ju] ", (uintmax_t)proc->pid);
+	if (multiproctrace) {
+		if (last_char == '\n')
+			fprintf(trace_fp, "[%ju] ", (uintmax_t)proc->pid);
+		else if (proc->pid != last_pid)
+			fprintf(trace_fp, "\n[%ju] ", (uintmax_t)proc->pid);
+	}
 	va_start(ap, fmt);
 	vfprintf(trace_fp, fmt, ap);
 	last_pid = proc->pid;