diff --git a/lib.nas b/lib.nas
index 83569df..9669f67 100644
--- a/lib.nas
+++ b/lib.nas
@@ -61,6 +61,11 @@ var floor=func(val){
     return __floor(val);
 }
 
+# exit using std::exit
+var exit=func(val=-1){
+    return __exit(val);
+}
+
 # abort using std::abort
 var abort=func(){
     __abort();
diff --git a/nasal_builtin.h b/nasal_builtin.h
index d25ec3c..a801782 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -56,6 +56,11 @@ nas_ref builtin_println(nas_ref* local,nasal_gc& gc)
     std::cout<<std::endl;
     return nil;
 }
+nas_ref builtin_exit(nas_ref* local,nasal_gc& gc)
+{
+    std::exit(local[1].num());
+    return nil;
+}
 nas_ref builtin_abort(nas_ref* local,nasal_gc& gc)
 {
     std::abort();
@@ -1153,6 +1158,7 @@ struct
 {
     {"__print",   builtin_print   },
     {"__println", builtin_println },
+    {"__exit",    builtin_exit    },
     {"__abort",   builtin_abort   },
     {"__append",  builtin_append  },
     {"__setsize", builtin_setsize },
diff --git a/stl/lib.nas b/stl/lib.nas
index 83569df..9669f67 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -61,6 +61,11 @@ var floor=func(val){
     return __floor(val);
 }
 
+# exit using std::exit
+var exit=func(val=-1){
+    return __exit(val);
+}
+
 # abort using std::abort
 var abort=func(){
     __abort();
diff --git a/test/calc.nas b/test/calc.nas
index d5b9f98..bd36c6d 100644
--- a/test/calc.nas
+++ b/test/calc.nas
@@ -70,6 +70,7 @@ var testfile=[
     "trait.nas        ",
     "turingmachine.nas",
     "utf8chk.nas      ",
+    "watchdog.nas     ",
     "wavecollapse.nas ",
     "ycombinator.nas  "
 ];
diff --git a/test/md5compare.nas b/test/md5compare.nas
index e852604..64102cb 100644
--- a/test/md5compare.nas
+++ b/test/md5compare.nas
@@ -53,12 +53,12 @@ var filechecksum=func(){
         "./test/md5.nas",          "./test/md5compare.nas",
         "./test/module_test.nas",  "./test/nasal_test.nas",
         "./test/occupation.nas",   "./test/pi.nas",
-        "./test/ppmgen.nas",
-        "./test/prime.nas",        "./test/qrcode.nas",
-        "./test/quick_sort.nas",   "./test/scalar.nas",
-        "./test/snake.nas",        "./test/tetris.nas",
-        "./test/trait.nas",        "./test/turingmachine.nas",
-        "./test/utf8chk.nas",      "./test/wavecollapse.nas",
+        "./test/ppmgen.nas",       "./test/prime.nas",
+        "./test/qrcode.nas",       "./test/quick_sort.nas",
+        "./test/scalar.nas",       "./test/snake.nas",
+        "./test/tetris.nas",       "./test/trait.nas",
+        "./test/turingmachine.nas","./test/utf8chk.nas",
+        "./test/watchdog.nas",     "./test/wavecollapse.nas",
         "./test/ycombinator.nas",  "LICENSE",
         "main.cpp",                "makefile",
         "nasal_ast.h",             "nasal_builtin.h",
diff --git a/test/watchdog.nas b/test/watchdog.nas
new file mode 100644
index 0000000..ff80b95
--- /dev/null
+++ b/test/watchdog.nas
@@ -0,0 +1,47 @@
+var os_time=func(){
+    return "[\e[33m"~os.time()~"\e[0m] ";
+}
+var err_hd=func(){
+    return "[\e[91merror\e[0m] ";
+}
+var watching_hd=func(){
+    return "[\e[96mwatching\e[0m] ";
+}
+var modified_hd=func(){
+    return "[\e[92mmodified\e[0m] ";
+}
+var usage=func(){
+    println(os_time(),"[\e[92musage\e[0m] nasal watchdog.nas <filename>");
+}
+
+var argv=runtime.argv();
+if(size(argv)!=1){
+    println(os_time(),err_hd(),"need correct file path to watch");
+    usage();
+    exit(-1);
+}
+var filename=argv[0];
+if(!io.exists(filename)){
+    println(os_time(),err_hd(),"file <",filename,"> does not exist");
+    usage();
+    exit(-1);
+}
+
+var modified_time=fstat(filename).st_mtime;
+println(os_time(),watching_hd(),filename," ..");
+while(1){
+    unix.sleep(1);
+    if(!io.exists(filename)){
+        println(os_time(),err_hd(),"file <",filename,"> does not exist");
+        break;
+    }
+    var latest_modified_time=fstat(filename).st_mtime;
+    if(latest_modified_time!=modified_time){
+        modified_time=latest_modified_time;
+        println(os_time(),modified_hd(),filename);
+        var ret=system((os.platform()=="windows"?"":"./")~"nasal "~filename);
+        if(ret!=0){
+            println(os_time(),err_hd(),"process returned value ",ret);
+        }
+    }
+}
\ No newline at end of file