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The stack script command

stack script [--package PACKAGE] FILE
             [-- ARGUMENT(S) (e.g. stack script X.hs -- argument(s) to program)]
             [--compile | --optimize] [--[no-]use-root] [--ghc-options OPTIONS]
             [--extra-dep PACKAGE-VERSION] [--no-run]

The stack script command either runs a specified Haskell source file (using GHC's runghc) or, optionally, compiles such a file (using GHC) and, by default, runs it.

Unlike stack ghc and stack runghc, the command ignores all Stack YAML configuration files (global and project-level). A snapshot must be specified on the command line (with the --resolver option). For example:

stack --resolver lts-20.4 MyScript.hs

or, equivalently:

stack script --resolver lts-20.4 MyScript.hs

The stack script command behaves as if the --install-ghc flag had been passed at the command line.

Everything after -- on the command line is interpreted as a command line argument to be passed to what is run.

A package can be added to the snapshot on the command line with the --extra-dep option (which can be specified multiple times).

Each required package can be specified by name on the command line with the --package option (which can be specified multiple times). A single --package option can also refer to a list of package names, separated by a space or comma character. If the package is not in the snapshot, the most recent version on Hackage will be obtained. If no packages are specified in that way, all the required packages that are in the snapshot will be deduced by reference to the import statements in the source file. The base package associated with the version of GHC specified by the snapshot is always available.

The source file can be compiled by passing either the --compile flag (no optimization) or the --optimize flag (compilation with optimization). If the file is compiled, passing the --no-run flag will mean the compiled code is not run.

By default, all the compilation outputs (including the executable) are written to the directory of the source file. Pass the --use-root flag to write such outputs to a script-specific location in the scripts directory of the Stack root. The location reflects the absolute path to the source file, but ignoring the drive. This can avoid clutter in the source file directory.

Additional options can be passed to GHC using the --ghc-options option.


For example, Haskell source file MyScript.hs at location <drive>Users/jane/my-project (where <drive> could be / on Unix-like operating systems or C:/ or similar on Windows):

module Main (main) where

import Data.List (intercalate)
import System.Environment (getArgs)

import Acme.Missiles (launchMissiles)

main :: IO ()
main = do
  advices <- getArgs
  putStrLn $ intercalate "\n" advices

can be compiled and run, with arguments, with:

stack --resolver lts-20.4 script --package acme-missiles --compile MyScript.hs -- "Don't panic!" "Duck and cover!"

All the compilation outputs (like Main.hi, Main.o, and the executable MyScript) will be written to the my-project directory.

If compiled and run with the additional flag --use-root, all the compilation outputs will be written to a directory named MyScript.hs at Users/jane/my-project/ in the scripts directory of the Stack root.