diff --git a/doc/tutorial.md b/doc/tutorial.md
index d2af8fc..6188298 100644
--- a/doc/tutorial.md
+++ b/doc/tutorial.md
@@ -113,11 +113,12 @@ This type is created by native-function of nasal. If want to define a new data t
 
 ## Operators
 
-Nasal has basic math operators `+` `-` `*` `/` and a special operator `~` that joints strings.
+Nasal has basic math operators `+` `-` `*` `/` and a special operator `~` that joints strings or vectors.
 
 ```javascript
 1+2-(1+3)*(2+4)/(16-9);
 "str1"~"str2";
+[0]~[1]; # should be [0, 1]
 ```
 
 For conditional expressions, operators `==` `!=` `<` `>` `<=` `>=` are used to compare two values.
@@ -162,6 +163,9 @@ a ~= "string";
 a ^= 0xff;
 a &= 0xca;
 a |= 0xba;
+
+a = [0];
+a ~= [1]; # should be [0, 1]
 ```
 
 Operator `??` is used to check left hand side value is `nil` or not, if not,
diff --git a/doc/tutorial_zh.md b/doc/tutorial_zh.md
index 9500456..62910ad 100644
--- a/doc/tutorial_zh.md
+++ b/doc/tutorial_zh.md
@@ -109,11 +109,12 @@ __`ghost`__ 是用来存储`C/C++`的一些复杂数据结构。这种类型的
 
 ## 运算符
 
-Nasal拥有基本的四种数学运算符 `+` `-` `*` `/`以及一个特别的运算符 `~`，用于拼接字符串。
+Nasal拥有基本的四种数学运算符 `+` `-` `*` `/`以及一个特别的运算符 `~`，用于拼接字符串或者数组。
 
 ```javascript
 1+2-(1+3)*(2+4)/(16-9);
 "str1"~"str2";
+[0]~[1]; # should be [0, 1]
 ```
 
 对于条件语句，可以使用`==` `!=` `<` `>` `<=` `>=`来比较数据。`and` `or` 与C/C++中 `&&` `||`运算符一致。
@@ -157,6 +158,9 @@ a ~= "string";
 a ^= 0xff;
 a &= 0xca;
 a |= 0xba;
+
+a = [0];
+a ~= [1]; # should be [0, 1]
 ```
 
 `??` 运算符用于检查左侧值是否为 `nil`，如果不是则返回右侧的值：
diff --git a/src/nasal_codegen.cpp b/src/nasal_codegen.cpp
index e68b3db..523be41 100644
--- a/src/nasal_codegen.cpp
+++ b/src/nasal_codegen.cpp
@@ -17,13 +17,16 @@ void codegen::load_native_function_table(nasal_builtin_table* table) {
             err.err("code", "\"" + std::string(table[i].name) + "\" conflicts.");
             continue;
         }
+
+        // replace unsafe native functions with redirect function in limit mode
         if (flag_limited_mode && unsafe_system_api.count(table[i].name)) {
             native_function.push_back({"__unsafe_redirect", builtin_unsafe});
         } else {
             native_function.push_back(table[i]);
         }
-        auto index = native_function_mapper.size();
+
         // insert into mapper
+        auto index = native_function_mapper.size();
         native_function_mapper[table[i].name] = index;
     }
 }
diff --git a/src/nasal_codegen.h b/src/nasal_codegen.h
index 8b4d123..961a105 100644
--- a/src/nasal_codegen.h
+++ b/src/nasal_codegen.h
@@ -57,8 +57,7 @@ private:
         // dylib
         "__dlopen", "__dlclose", "__dlcallv", "__dlcall",
         // unix
-        "__pipe", "__fork", "__waitpid", "__chdir",
-        "__environ", "__getcwd", "__getenv",
+        "__chdir", "__environ", "__getcwd", "__getenv",
         // subprocess
         "__subprocess_create",
         "__subprocess_terminate"
diff --git a/src/nasal_vm.h b/src/nasal_vm.h
index 27b9678..89b9cf3 100644
--- a/src/nasal_vm.h
+++ b/src/nasal_vm.h
@@ -536,6 +536,22 @@ inline void vm::o_subeq() {op_calc_eq(-);}
 inline void vm::o_muleq() {op_calc_eq(*);}
 inline void vm::o_diveq() {op_calc_eq(/);}
 inline void vm::o_lnkeq() {
+    // concat two vectors into one
+    if (ctx.top[-1].is_vec() && ctx.memr[0].is_vec()) {
+        ngc.temp = ngc.alloc(vm_type::vm_vec);
+        for(auto i : ctx.memr[0].vec().elems) {
+            ngc.temp.vec().elems.push_back(i);
+        }
+        for(auto i : ctx.top[-1].vec().elems) {
+            ngc.temp.vec().elems.push_back(i);
+        }
+        ctx.top[-1] = ctx.memr[0] = ngc.temp;
+        ngc.temp = nil;
+        ctx.memr = nullptr;
+        ctx.top -= imm[ctx.pc]+1;
+        return;
+    }
+
     ctx.top[-1] = ctx.memr[0] = ngc.newstr(
         ctx.memr[0].to_str()+ctx.top[-1].to_str()
     );
diff --git a/src/natives/unix_lib.cpp b/src/natives/unix_lib.cpp
index f394734..a23ddd5 100644
--- a/src/natives/unix_lib.cpp
+++ b/src/natives/unix_lib.cpp
@@ -12,48 +12,6 @@ void dir_entry_destructor(void* ptr) {
 #endif
 }
 
-var builtin_pipe(context* ctx, gc* ngc) {
-#ifndef _WIN32
-    i32 fd[2];
-    var res = ngc->alloc(vm_type::vm_vec);
-    if (pipe(fd)==-1) {
-        return nas_err("unix::pipe", "failed to create pipe");
-    }
-    res.vec().elems.push_back(var::num(static_cast<f64>(fd[0])));
-    res.vec().elems.push_back(var::num(static_cast<f64>(fd[1])));
-    return res;
-#endif
-    return nas_err("unix::pipe", "not supported on windows");
-}
-
-var builtin_fork(context* ctx, gc* ngc) {
-#ifndef _WIN32
-    f64 res = fork();
-    if (res<0) {
-        return nas_err("unix::fork", "failed to fork a process");
-    }
-    return var::num(static_cast<f64>(res));
-#endif
-    return nas_err("unix::fork", "not supported on windows");
-}
-
-var builtin_waitpid(context* ctx, gc* ngc) {
-    auto pid = ctx->localr[1];
-    auto nohang = ctx->localr[2];
-    if (!pid.is_num() || !nohang.is_num()) {
-        return nas_err("unix::waitpid", "pid and nohang must be number");
-    }
-#ifndef _WIN32
-    i32 ret_pid, status;
-    ret_pid = waitpid(pid.num(), &status, nohang.num()==0? 0:WNOHANG);
-    var vec = ngc->alloc(vm_type::vm_vec);
-    vec.vec().elems.push_back(var::num(static_cast<f64>(ret_pid)));
-    vec.vec().elems.push_back(var::num(static_cast<f64>(status)));
-    return vec;
-#endif
-    return nas_err("unix::waitpid", "not supported on windows");
-}
-
 var builtin_opendir(context* ctx, gc* ngc) {
     auto path = ctx->localr[1];
     if (!path.is_str()) {
@@ -139,9 +97,6 @@ var builtin_getenv(context* ctx, gc* ngc) {
 }
 
 nasal_builtin_table unix_lib_native[] = {
-    {"__pipe", builtin_pipe},
-    {"__fork", builtin_fork},
-    {"__waitpid", builtin_waitpid},
     {"__opendir", builtin_opendir},
     {"__readdir", builtin_readdir},
     {"__closedir", builtin_closedir},
diff --git a/src/natives/unix_lib.h b/src/natives/unix_lib.h
index 93a70aa..6ea292b 100644
--- a/src/natives/unix_lib.h
+++ b/src/natives/unix_lib.h
@@ -24,9 +24,6 @@ namespace nasal {
 
 void dir_entry_destructor(void*);
 
-var builtin_pipe(context*, gc*);
-var builtin_fork(context*, gc*);
-var builtin_waitpid(context*, gc*);
 var builtin_opendir(context*, gc*);
 var builtin_readdir(context*, gc*);
 var builtin_closedir(context*, gc*);
diff --git a/std/unix.nas b/std/unix.nas
index a966c09..714f46f 100644
--- a/std/unix.nas
+++ b/std/unix.nas
@@ -7,26 +7,6 @@ use std.io;
 var _S_IFDIR = 0x4000;
 var _S_IFREG = 0x8000;
 
-var pipe = func() {
-    return __pipe;
-}
-
-var fork = func() {
-    return __fork;
-}
-
-var dup2 = func(fd0, fd1) {
-    die("not supported yet");
-}
-
-var exec = func(filename, argv, envp) {
-    die("not supported yet");
-}
-
-var waitpid = func(pid, nohang = 0) {
-    return __waitpid;
-}
-
 var isdir = func(path) {
     return !!bits.u32_and(io.stat(path)[2], _S_IFDIR);
 }