The -s flag includes staying quiet about missing files.
diff --git a/toys/cmp.c b/toys/cmp.c
index 87fbe02..42325a1 100644
--- a/toys/cmp.c
+++ b/toys/cmp.c
@@ -87,6 +87,6 @@
 
 void cmp_main(void)
 {
-	loopfiles(toys.optargs, do_cmp);
+	loopfiles_rw(toys.optargs, O_RDONLY, 0, toys.optflags&FLAG_s, do_cmp);
 }