diff --git a/Cargo.lock b/Cargo.lock
index ae230e9..3880066 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -921,7 +921,7 @@ checksum = "5b40af805b3121feab8a3c29f04d8ad262fa8e0561883e7653e024ae4479e6de"
 
 [[package]]
 name = "pretty-derby"
-version = "0.4.0"
+version = "0.4.1"
 dependencies = [
  "chrono",
  "clap",
diff --git a/Cargo.toml b/Cargo.toml
index cce04a4..ff5f300 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "pretty-derby"
 authors = ["Phie Ash"]
 description = "Hachimi hachimi hachimi~"
-version = "0.4.1"
+version = "0.4.2"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
diff --git a/flake.lock b/flake.lock
index c1ed282..b06f282 100644
--- a/flake.lock
+++ b/flake.lock
@@ -2,23 +2,20 @@
   "nodes": {
     "fenix": {
       "inputs": {
-        "nixpkgs": [
-          "nixpkgs"
-        ],
+        "nixpkgs": "nixpkgs",
         "rust-analyzer-src": "rust-analyzer-src"
       },
       "locked": {
-        "lastModified": 1709878902,
-        "narHash": "sha256-4cVeNZMZWUIf9XS285BD4VPPco1CosBLq4pc0aL5IUA=",
+        "lastModified": 1714199028,
+        "narHash": "sha256-QO3Yv3UfJRfhZE1wsHOartg+k8/Kf1BiDyfl8eEpqcE=",
         "owner": "nix-community",
         "repo": "fenix",
-        "rev": "3c913ad893d6304a637b5383057bdab5543e9e92",
+        "rev": "055f6db376eaf544d84aa55bd5a7c70634af41ba",
         "type": "github"
       },
       "original": {
-        "owner": "nix-community",
-        "repo": "fenix",
-        "type": "github"
+        "id": "fenix",
+        "type": "indirect"
       }
     },
     "flake-utils": {
@@ -26,17 +23,16 @@
         "systems": "systems"
       },
       "locked": {
-        "lastModified": 1709126324,
-        "narHash": "sha256-q6EQdSeUZOG26WelxqkmR7kArjgWCdw5sfJVHPH/7j8=",
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
         "owner": "numtide",
         "repo": "flake-utils",
-        "rev": "d465f4819400de7c8d874d50b982301f28a84605",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
         "type": "github"
       },
       "original": {
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "type": "github"
+        "id": "flake-utils",
+        "type": "indirect"
       }
     },
     "naersk": {
@@ -61,26 +57,40 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1709703039,
-        "narHash": "sha256-6hqgQ8OK6gsMu1VtcGKBxKQInRLHtzulDo9Z5jxHEFY=",
-        "owner": "NixOS",
+        "lastModified": 1714076141,
+        "narHash": "sha256-Drmja/f5MRHZCskS6mvzFqxEaZMeciScCTFxWVLqWEY=",
+        "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "9df3e30ce24fd28c7b3e2de0d986769db5d6225d",
+        "rev": "7bb2ccd8cdc44c91edba16c48d2c8f331fb3d856",
         "type": "github"
       },
       "original": {
-        "owner": "NixOS",
+        "owner": "nixos",
         "ref": "nixos-unstable",
         "repo": "nixpkgs",
         "type": "github"
       }
     },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1714091391,
+        "narHash": "sha256-68n3GBvlm1MIeJXadPzQ3v8Y9sIW3zmv8gI5w5sliC8=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "4c86138ce486d601d956a165e2f7a0fc029a03c1",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
     "root": {
       "inputs": {
         "fenix": "fenix",
         "flake-utils": "flake-utils",
         "naersk": "naersk",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs_2"
       }
     },
     "rust-analyzer-src": {
diff --git a/flake.nix b/flake.nix
index 3ca9a5b..ddcf910 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,58 +1,56 @@
 {
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
-    fenix = {
-      url = "github:nix-community/fenix";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-    flake-utils.url = "github:numtide/flake-utils";
     naersk = {
       url = "github:nix-community/naersk";
       inputs.nixpkgs.follows = "nixpkgs";
     };
   };
 
-  outputs = { fenix, flake-utils, naersk, nixpkgs, self }:
+  outputs =
     {
-      overlays = rec {
-        dev = final: prev:
-          let
-            system = final.hostPlatform.system;
-            toolchain = with fenix.packages.${system}; combine [
+      fenix,
+      flake-utils,
+      naersk,
+      nixpkgs,
+      self,
+    }:
+    {
+      overlays.default =
+        final: prev:
+        let
+          inherit (final.hostPlatform) system;
+          toolchain =
+            with fenix.packages.${system};
+            combine [
               minimal.cargo
               minimal.rustc
             ];
-            naersk-lib = naersk.lib.${system}.override {
-              cargo = toolchain;
-              rustc = toolchain;
-            };
-          in
-          {
-            pretty-derby = naersk-lib.buildPackage {
-              nativeBuildInputs = with final; lib.optional stdenv.isDarwin [
-                darwin.apple_sdk.frameworks.SystemConfiguration
-              ];
-              src = ./.;
-            };
-
-            pretty-derby-shell = with final; mkShell {
-              buildInputs = [
-                toolchain
-                iconv
-              ] ++ (lib.optional stdenv.isDarwin [
-                darwin.apple_sdk.frameworks.SystemConfiguration
-              ]);
-            };
+          naersk-lib = naersk.lib.${system}.override {
+            cargo = toolchain;
+            rustc = toolchain;
           };
-
-        default = final: prev: { inherit (dev) pretty-derby; };
-      };
-    } //
-    (flake-utils.lib.eachDefaultSystem (system:
+        in
+        {
+          pretty-derby = naersk-lib.buildPackage {
+            nativeBuildInputs =
+              with final;
+              (lib.optional stdenv.isDarwin [ darwin.apple_sdk.frameworks.SystemConfiguration ])
+              ++ [ installShellFiles ];
+            src = ./.;
+            postFixup = ''
+              for shell in bash fish zsh; do
+                installShellCompletion --cmd pretty-derby --$shell <($out/bin/pretty-derby --completion $shell)
+              done
+            '';
+          };
+        };
+    }
+    // (flake-utils.lib.eachDefaultSystem (
+      system:
       let
         pkgs = (import nixpkgs) {
           inherit system;
-          overlays = [ self.overlays.dev ];
+          overlays = [ self.overlays.default ];
         };
       in
       {
@@ -61,7 +59,16 @@
           default = pretty-derby;
         };
 
+        devShells.default =
+          with pkgs;
+          mkShell {
+            buildInputs = [
+              toolchain
+              iconv
+            ] ++ (lib.optional stdenv.isDarwin [ darwin.apple_sdk.frameworks.SystemConfiguration ]);
+          };
 
-        devShells.default = pkgs.pretty-derby-shell;
-      }));
+        formatter = pkgs.nixfmt-rfc-style;
+      }
+    ));
 }
diff --git a/src/main.rs b/src/main.rs
index 212e81b..9427f7b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -25,8 +25,8 @@ struct Cli {
     #[arg(short, long, action = ArgAction::Count)]
     verbose: u8,
 
-    #[arg(long = "generate", action = ArgAction::Set)]
-    generator: Option<Shell>,
+    #[arg(long, value_name = "SHELL")]
+    completion: Option<Shell>,
 }
 
 #[tokio::main]
@@ -39,7 +39,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
         _ => (Level::Trace, LevelFilter::Trace),
     };
 
-    if let Some(generator) = cli.generator {
+    if let Some(generator) = cli.completion {
         let mut cmd = Cli::command();
         let name = cmd.get_name().to_string();
         generate(generator, &mut cmd, name, &mut io::stdout());