Control.Monad.Shell

A shell script monad

Documentation

data Script a

Shell script monad.

Instances

Monad Script

script :: Script f -> Text

Generates a shell script, including hashbang, suitable to be written to a file.

linearScript :: Script f -> Text

Generates a single line of shell code.

data Var

A shell variable.

Instances

Eq Var

Ord Var

Show Var

val :: Var -> Q

Expand a shell variable to its value.

data Expr

A shell expression.

indent :: Expr -> Expr

Indents an Expr

run :: Text -> [Text] -> Script ()

Adds a shell command to the script.

cmd :: ShellCmd result => Text -> result

Variadic argument version of run.

The command can be passed any number of arguments. As well as passing Text arguments, it also accepts Var arguments, which passes the value of a shell variable to the command.

Convenient usage of cmd requires the following:

{-# LANGUAGE OverloadedStrings, ExtendedDefaultRules #-}
{-# OPTIONS_GHC -fno-warn-type-defaults #-}
import Control.Monad.Shell
import qualified Data.Text.Lazy as T
default (L.Text)

This allows writing, for example:

demo = script $ do
  cmd "echo" "hello, world"
  name <- newVar "name"
  readVar name
  cmd "echo" "hello" name

add :: Expr -> Script ()

Adds an Expr to the script.

comment :: Text -> Script ()

Adds a comment that is embedded in the generated shell script.

newVar

Arguments

:: Text

base of variable name

-> Script Var

Defines a new shell variable.

The name of the variable that appears in the shell script will be based on provided name, but each call to newVar will generate a new, unique variable name.

newVarContaining

Arguments

:: Text

base of variable name

-> Text

value

-> Script Var

Creates a new shell variable, with an initial value.

globalVar :: Text -> Script Var

Gets a Var that refers to a global variable, such as PATH

func :: Script () -> Script (Script ())

Defines a shell function, and returns an action that can be run to call the function.

TODO parameter passing to the function

forCmd :: Script () -> (Var -> Script ()) -> Script ()

Runs the command, and separates its output into parts (using the IFS)

The action is run for each part, passed a Var containing the part.

quote :: Text -> Q

Quotes the value to allow it to be safely exposed to the shell.

The method used is to replace ' with '"'"' and wrap the value inside single quotes. This works for POSIX shells, as well as other shells like csh.

readVar :: Var -> Script ()

Generates shell code to read a variable from stdin.

(-|-) :: Script () -> Script () -> Script ()

Pipes together two Scripts.