diff --git a/CHANGELOG.md b/CHANGELOG.md
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--- /dev/null
+++ b/CHANGELOG.md
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+# Changelog
+
+`gw` uses [PVP Versioning][1].
+The changelog is available [on GitHub][2].
+
+0.0.0
+=====
+
+* Initially created.
+
+[1]: https://pvp.haskell.org
+[2]: https://github.com/chessai/gw/releases
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+BSD 3-Clause License
+
+Copyright (c) 2019, chessai
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
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+# gw
+
+[![Hackage](https://img.shields.io/hackage/v/gw.svg)](https://hackage.haskell.org/package/gw)
+[![BSD3 license](https://img.shields.io/badge/license-BSD3-blue.svg)](LICENSE)
+
+ghcWithPackages cmdline util
diff --git a/app/Main.hs b/app/Main.hs
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--- /dev/null
+++ b/app/Main.hs
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+{-# language DerivingStrategies #-}
+{-# language GeneralizedNewtypeDeriving #-}
+{-# language LambdaCase #-}
+{-# language OverloadedStrings #-}
+{-# language ScopedTypeVariables #-}
+{-# language ViewPatterns #-}
+
+module Main
+  ( main
+  ) where
+
+import System.Environment (getArgs)
+import qualified Data.List as List
+import qualified System.Posix.Process as P
+
+main :: IO ()
+main = parseArgs >>= runCmd
+
+parseArgs :: IO Cmd
+parseArgs = getArgs >>= \case
+  [] -> pure Help
+  ("-v":_) -> pure Version
+  ("--version":_) -> pure Version
+  ("-h":_) -> pure Help
+  ("--help":_) -> pure Help
+  ("-p":xs) -> go Pure xs
+  ("--pure":xs) -> go Pure xs
+  xs -> go Impure xs
+  where
+    go :: Purity -> [String] -> IO Cmd
+    go p = \case
+      [] -> pure BadCmd
+      (x:xs) -> case readGhc x of
+        Left str -> do
+          putStr (str ++ "\n")
+          pure BadCmd
+        Right g -> pure $ GhcWith p g (PkgSet xs)
+
+ghcWith :: Ghc -> PkgSet -> String
+ghcWith (showGhc -> ghc) (showPkgSet -> pkgs) = mconcat
+  [ "haskell.packages."
+  , ghc
+  , ".ghcWithPackages (pkgs: with pkgs; [ "
+  , pkgs
+  , " ])"
+  ]
+
+ghcWithIO :: Ghc -> PkgSet -> Purity -> IO ()
+ghcWithIO g pkgs p
+  = P.executeFile "nix-shell" True (p' ++ ["-p",ghcWith g pkgs]) Nothing 
+  where
+    p' = case p of
+      Pure -> ["--pure"]
+      Impure -> []
+
+data Cmd
+  = Help
+  | Version
+  | GhcWith Purity Ghc PkgSet
+  | BadCmd
+
+runCmd :: Cmd -> IO ()
+runCmd = \case
+  Help -> putStr help
+  Version -> putStr version
+  GhcWith p g pkgs -> ghcWithIO g pkgs p
+  BadCmd -> putStr badCmd
+
+help,version,badCmd :: String
+help = mconcat
+  [ "\n"
+  , "    gw - a utility for entering a nix-shell using ghcWithPackages\n\n"
+  , "    Usage: gw <OPTIONS> <GHC> <PKGS>\n\n"
+  , "    Available options:\n"
+  , "      -h,--help            Display this help menu\n"
+  , "      -p,--pure            Enter a pure nix-shell\n"
+  , "      -v,--version         Display the version of gw\n"
+  , "\n"
+  ]
+version = "gw 0.1"
+badCmd = mconcat
+  [ "\n"
+  , "Malformed command. Help menu:\n"
+  , help
+  ]
+
+readGhc :: String -> Either String Ghc
+readGhc = \case
+  "ghc710" -> Right Ghc710
+  "ghc801" -> Right Ghc801
+  "ghc802" -> Right Ghc802
+  "ghc821" -> Right Ghc821
+  "ghc822" -> Right Ghc822
+  "ghc841" -> Right Ghc841
+  "ghc842" -> Right Ghc842
+  "ghc843" -> Right Ghc843
+  "ghc844" -> Right Ghc844
+  "ghc861" -> Right Ghc861
+  "ghc862" -> Right Ghc862
+  "ghc863" -> Right Ghc863
+  "ghc864" -> Right Ghc864
+  "ghc865" -> Right Ghc865
+  "ghcHEAD" -> Right GhcHead
+  x -> Left $ "GHC arg \"" ++ x ++ "\" passed is not one of " ++ ghcSet
+
+showGhc :: Ghc -> String
+showGhc = \case
+  Ghc710 -> "ghc710"
+  Ghc801 -> "ghc801"
+  Ghc802 -> "ghc802"
+  Ghc821 -> "ghc821"
+  Ghc822 -> "ghc822"
+  Ghc841 -> "ghc841"
+  Ghc842 -> "ghc842"
+  Ghc843 -> "ghc843"
+  Ghc844 -> "ghc844"
+  Ghc861 -> "ghc861"
+  Ghc862 -> "ghc862"
+  Ghc863 -> "ghc863"
+  Ghc864 -> "ghc864"
+  Ghc865 -> "ghc865"
+  GhcHead -> "ghcHEAD"
+ 
+data Ghc
+  = Ghc710
+  | Ghc801
+  | Ghc802
+  | Ghc821
+  | Ghc822
+  | Ghc841
+  | Ghc842
+  | Ghc843
+  | Ghc844
+  | Ghc861
+  | Ghc862
+  | Ghc863
+  | Ghc864
+  | Ghc865
+  | GhcHead
+  deriving stock (Eq,Ord,Enum,Bounded,Show)
+
+ghcSet :: String
+ghcSet = mconcat
+  [ "{"
+  , (List.intercalate ", " (map showGhc [minBound..maxBound :: Ghc]))
+  , "}"
+  ]
+
+newtype PkgSet = PkgSet [String]
+  deriving newtype (Eq,Show)
+
+showPkgSet :: PkgSet -> String
+showPkgSet (PkgSet set) = List.unwords set
+
+data Purity = Pure | Impure
+  deriving stock (Eq,Show)
diff --git a/gw.cabal b/gw.cabal
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--- /dev/null
+++ b/gw.cabal
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+cabal-version: 2.2
+name:
+  gw
+version:
+  0.1
+synopsis:
+  ghcWithPackages cmdline util
+description:
+  ghcWithPackages cmdline util. supports:
+  . 
+    * multiple ghc versions
+  .  
+    * pure/impure nix-shell
+  .   
+    * entering shell with multiple packages available
+   
+homepage:
+  https://github.com/chessai/gw
+bug-reports:
+  https://github.com/chessai/gw/issues
+license:
+  BSD-3-Clause
+license-file:
+  LICENSE
+author:
+  chessai
+maintainer:
+  chessai <chessai1996@gmail.com>
+copyright:
+  © 2019 chessai
+category:
+  Utility
+build-type:
+  Simple
+extra-doc-files:
+    README.md
+  , CHANGELOG.md
+tested-with:
+  GHC == 8.2.2, GHC == 8.4.4, GHC == 8.6.3
+
+executable gw
+  hs-source-dirs:
+    app
+  main-is:
+    Main.hs
+  build-depends:
+    , base >= 4.10.1 && < 4.13
+    , unix >= 2.7 && < 2.8
+  ghc-options:
+    -Wall
+  default-language:
+    Haskell2010
+
+source-repository head
+  type:
+    git
+  location:
+    https://github.com/chessai/gw.git