ptrap: fail if invoked with no arguments

diff --git a/sys/src/cmd/ptrap.c b/sys/src/cmd/ptrap.c
index 30a4db07f83b4b1592840e26c3f756fb26a4d0ea..7cf60f7d431195b6f481884b2cff6944a28f3ad4 100644 (file)
--- a/sys/src/cmd/ptrap.c
+++ b/sys/src/cmd/ptrap.c
@@ -356,7 +356,7 @@ threadmain(int argc, char **argv)
        default: usage();
        }ARGEND;
 
-       if(argc % 2) usage();
+       if(argc == 0 || argc % 2) usage();
        for(i = 0; i < argc; i += 2){
                f = emalloc9p(sizeof(PFilter));
                f->name = strdup(argv[i]);