Control.Monad.Shell

This is a shell monad, for generating shell scripts.

The emphasis is on generating shell code that will work in any POSIX compliant shell and avoids many common shell pitfalls, including insufficient quoting, while allowing the Haskell type checker to be leveraged for additional safety.

Here is a hello world example.

{-# LANGUAGE OverloadedStrings, ExtendedDefaultRules #-}
import Control.Monad.Shell
import Data.Monoid
import qualified Data.Text.Lazy as T
import qualified Data.Text.Lazy.IO as T
default (T.Text)

main :: IO ()
main = T.writeFile "hello.sh" $ script $ do
	cmd "echo" "hello, world"
	username <- newVarFrom (Output (cmd "whoami")) ()
	cmd "echo" "from" (WithVar username (<> "'s shell"))

When run, that generates this shell code:

#!/bin/sh
echo 'hello, world'
_v="$(whoami)"
echo from "$_v"''"'"'s shell'

There are several other examples shipped in the examples/ directory of the shell-monad package. For example, protocol.hs shows how shell-monad can be used to implement a shell script that speaks a protocol that is defined using Haskell data types.

Core

data Script a

Shell script monad.

Instances

Monad Script

Defined in Control.Monad.Shell

Methods

(>>=) :: Script a -> (a -> Script b) -> Script b

(>>) :: Script a -> Script b -> Script b

return :: a -> Script a

Functor Script

Defined in Control.Monad.Shell

Methods

fmap :: (a -> b) -> Script a -> Script b

(<$) :: a -> Script b -> Script a

Applicative Script

Defined in Control.Monad.Shell

Methods

pure :: a -> Script a

(<*>) :: Script (a -> b) -> Script a -> Script b

liftA2 :: (a -> b -> c) -> Script a -> Script b -> Script c

(*>) :: Script a -> Script b -> Script b

(<*) :: Script a -> Script b -> Script a

f ~ () => CmdParams (Script f)

Defined in Control.Monad.Shell

Methods

cmdAll :: (Env -> Text) -> [Env -> Text] -> Script f

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 Term t a

A term that can be expanded in a shell command line.

Instances

(Show a, Num a) => Num (Term Static a)

Defined in Control.Monad.Shell

Methods

(+) :: Term Static a -> Term Static a -> Term Static a

(-) :: Term Static a -> Term Static a -> Term Static a

(*) :: Term Static a -> Term Static a -> Term Static a

negate :: Term Static a -> Term Static a

abs :: Term Static a -> Term Static a

signum :: Term Static a -> Term Static a

fromInteger :: Integer -> Term Static a

Show a => Param (Term Static a)

Defined in Control.Monad.Shell

Methods

toTextParam :: Term Static a -> Env -> Text

Param (Term Var a)

Defined in Control.Monad.Shell

Methods

toTextParam :: Term Var a -> Env -> Text

data Var

Used to represent a shell variable.

Instances

Param (Term Var a)

Defined in Control.Monad.Shell

Methods

toTextParam :: Term Var a -> Env -> Text

data Static

Used for a static value.

Instances

(Show a, Num a) => Num (Term Static a)

Defined in Control.Monad.Shell

Methods

(+) :: Term Static a -> Term Static a -> Term Static a

(-) :: Term Static a -> Term Static a -> Term Static a

(*) :: Term Static a -> Term Static a -> Term Static a

negate :: Term Static a -> Term Static a

abs :: Term Static a -> Term Static a

signum :: Term Static a -> Term Static a

fromInteger :: Integer -> Term Static a

Show a => Param (Term Static a)

Defined in Control.Monad.Shell

Methods

toTextParam :: Term Static a -> Env -> Text

data Quoted a

A value that is safely quoted so that it can be exposed to the shell.

While the constructor is exposed, you should avoid directly constucting Quoted values. Instead, use quote.

Instances

Eq a => Eq (Quoted a)

Defined in Control.Monad.Shell.Quote

Methods

(==) :: Quoted a -> Quoted a -> Bool

(/=) :: Quoted a -> Quoted a -> Bool

Ord a => Ord (Quoted a)

Defined in Control.Monad.Shell.Quote

Methods

compare :: Quoted a -> Quoted a -> Ordering

(<) :: Quoted a -> Quoted a -> Bool

(<=) :: Quoted a -> Quoted a -> Bool

(>) :: Quoted a -> Quoted a -> Bool

(>=) :: Quoted a -> Quoted a -> Bool

max :: Quoted a -> Quoted a -> Quoted a

min :: Quoted a -> Quoted a -> Quoted a

Show a => Show (Quoted a)

Defined in Control.Monad.Shell.Quote

Methods

showsPrec :: Int -> Quoted a -> ShowS

show :: Quoted a -> String

showList :: [Quoted a] -> ShowS

IsString (Quoted Text)

Defined in Control.Monad.Shell.Quote

Methods

fromString :: String -> Quoted Text

Semigroup a => Semigroup (Quoted a)

Defined in Control.Monad.Shell.Quote

Methods

(<>) :: Quoted a -> Quoted a -> Quoted a

sconcat :: NonEmpty (Quoted a) -> Quoted a

stimes :: Integral b => b -> Quoted a -> Quoted a

Monoid a => Monoid (Quoted a)

Defined in Control.Monad.Shell.Quote

Methods

mempty :: Quoted a

mappend :: Quoted a -> Quoted a -> Quoted a

mconcat :: [Quoted a] -> Quoted a

Param (Quoted Text)

Quoted Text arguments are passed as-is.

Defined in Control.Monad.Shell

Methods

toTextParam :: Quoted Text -> Env -> Text

class Quotable t where

Quotes a 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.

The single quotes are omitted for simple values that do not need any quoting.

Methods

quote :: t -> Quoted Text

Instances

Quotable String

Defined in Control.Monad.Shell.Quote

Methods

quote :: String -> Quoted Text

Quotable Text

Defined in Control.Monad.Shell.Quote

Methods

quote :: Text -> Quoted Text

Show v => Quotable (Val v)

Defined in Control.Monad.Shell.Quote

Methods

quote :: Val v -> Quoted Text

Quotable (Val String)

Defined in Control.Monad.Shell.Quote

Methods

quote :: Val String -> Quoted Text

Quotable (Val Text)

Defined in Control.Monad.Shell.Quote

Methods

quote :: Val Text -> Quoted Text

glob :: Text -> Quoted Text

Treats the Text as a glob.

When used as a Param to a command, it expands to one parameter per matching file.

forCmd (cmd "ls" (glob "*/*.cabal")) $ \file ->
    cmd "echo" file

When used in a caseOf, it matches text against the glob.

The input is assumed to be a well-formed glob. Characters in it that are not alphanumeric and are not wildcard characters will be escaped before it is exposed to the shell. This allows eg, spaces in globs.

Running commands

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

Adds a shell command to the script.

cmd :: (Param command, CmdParams params) => command -> params

Variadic and polymorphic version of run

A command can be passed any number of Params.

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

For the most efficient use of cmd, add the following boilerplate, which will make string literals in your program default to being Text:

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

Note that the command to run is itself a Param, so it can be a Text, or a String, or even a Var or Output. For example, this echos "hi":

demo = script $ do
   echovar <- newVarContaining "echo" ()
   cmd echovar "hi"

class Param a

A Param is anything that can be used as the parameter of a command.

Minimal complete definition

toTextParam

Instances

Param String

String arguments are automatically quoted.

Defined in Control.Monad.Shell

Methods

toTextParam :: String -> Env -> Text

Param Text

Text arguments are automatically quoted.

Defined in Control.Monad.Shell

Methods

toTextParam :: Text -> Env -> Text

Param Arith

Allows passing an Arithmetic Expression as a parameter.

Defined in Control.Monad.Shell

Methods

toTextParam :: Arith -> Env -> Text

Param Output

Allows passing the output of a command as a parameter.

Defined in Control.Monad.Shell

Methods

toTextParam :: Output -> Env -> Text

Param (Quoted Text)

Quoted Text arguments are passed as-is.

Defined in Control.Monad.Shell

Methods

toTextParam :: Quoted Text -> Env -> Text

Param (WithVar a)

Allows modifying the value of a shell variable before it is passed to the command.

Defined in Control.Monad.Shell

Methods

toTextParam :: WithVar a -> Env -> Text

Show a => Param (Term Static a)

Defined in Control.Monad.Shell

Methods

toTextParam :: Term Static a -> Env -> Text

Param (Term Var a)

Defined in Control.Monad.Shell

Methods

toTextParam :: Term Var a -> Env -> Text

class CmdParams t

Allows a function to take any number of Params.

Minimal complete definition

cmdAll

Instances

f ~ () => CmdParams (Script f)

Defined in Control.Monad.Shell

Methods

cmdAll :: (Env -> Text) -> [Env -> Text] -> Script f

(Param arg, CmdParams result) => CmdParams (arg -> result)

Defined in Control.Monad.Shell

Methods

cmdAll :: (Env -> Text) -> [Env -> Text] -> arg -> result

newtype Output

The output of a command, or even a more complicated Script can be passed as a parameter to cmd

Examples:

cmd "echo" "hello there," (Output (cmd "whoami"))
cmd "echo" "root's pwent" (Output (cmd "cat" "/etc/passwd" -|- cmd "grep" "root"))

Constructors

Output (Script ())

Instances

Param Output

Allows passing the output of a command as a parameter.

Defined in Control.Monad.Shell

Methods

toTextParam :: Output -> Env -> Text

Shell variables

newtype NamedLike

Suggests that a shell variable or function have its name contain the specified Text.

Constructors

NamedLike Text

Instances

NameHinted NamedLike

Defined in Control.Monad.Shell

Methods

hinted :: (Maybe Text -> a) -> NamedLike -> a

class NameHinted h

Class of values that provide a hint for the name to use for a shell variable or function.

If you don't want to provide a naming hint, use ().

v1 <- newVar ()

To provide a naming hint, use NamedLike.

v1 <- newVar (NamedLike "x")

Minimal complete definition

hinted

Instances

NameHinted ()

Defined in Control.Monad.Shell

Methods

hinted :: (Maybe Text -> a) -> () -> a

NameHinted NamedLike

Defined in Control.Monad.Shell

Methods

hinted :: (Maybe Text -> a) -> NamedLike -> a

NameHinted (Maybe Text)

Defined in Control.Monad.Shell

Methods

hinted :: (Maybe Text -> a) -> Maybe Text -> a

static :: Quotable (Val t) => t -> Term Static t

Makes a Static Term from any value that can be shown.

newVar :: NameHinted namehint => forall a. namehint -> Script (Term Var a)

Defines a new shell variable, which starts out not being set.

Each call to newVar will generate a new, unique variable name.

The namehint can influence this name, but is modified to ensure uniqueness.

newVarFrom :: (NameHinted namehint, Param param) => param -> namehint -> Script (Term Var t)

Creates a new shell variable with an initial value coming from any Param.

For example,

packageName <- newVarFrom
     (Output $
         cmd "grep" "-i" "name\\s*:" (glob "*.cabal") -|-
         cmd "perl" "-pe" "s/^name\\s*:\\s*//i")
     (NamedLike "packageName")

Use this with WithVar to store to modified value of a variable in a new variable.

home <- globalVar "HOME"
cabalDir <- newVarFrom (WithVar home (<> "/.cabal")) ()

Or to capture the output of an arithmetic operation.

sum <- newVarFrom (val x `APlus` 1) ()

newVarContaining :: (NameHinted namehint, Quotable (Val t)) => t -> namehint -> Script (Term Var t)

Creates a new shell variable, with an initial value which can be anything that can be shown.

s <- newVarContaining "foo bar baz" (NamedLike "s")
i <- newVarContaining (1 :: Int) (NamedLike "i")

setVar :: Param param => forall a. Term Var a -> param -> Script ()

Sets the Var to the value of the param.

globalVar :: forall a. Text -> Script (Term Var a)

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

positionalParameters :: forall a. Term Var a

This special Var expands to whatever parameters were passed to the shell script.

Inside a func, it expands to whatever parameters were passed to the func.

(This is $@ in shell)

takeParameter :: NameHinted namehint => forall a. namehint -> Script (Term Var a)

Takes the first positional parameter, removing it from positionalParameters and returning a new Var that holds the value of the parameter.

If there are no more positional parameters, the script will crash with an error.

For example:

removefirstfile = script $ do
  cmd "rm" =<< takeParameter
  cmd "echo" "remaining parameters:" positionalParameters

defaultVar :: Param param => forall a. Term Var a -> param -> Script (Term Var a)

Generates a new Var. Expanding this Var will yield the same result as expanding the input Var, unless it is empty, in which case it instead defaults to the expansion of the param.

whenVar :: Param param => forall a. Term Var a -> param -> Script (Term Var a)

Generates a new Var. If the input Var is empty, then this new Var will likewise expand to the empty string. But if not, the new Var expands to the param.

lengthVar :: forall a. Term Var a -> Script (Term Var Integer)

Generates a new Var, which expands to the length of the expansion of the input Var.

Note that 'lengthVar positionalParameters' expands to the number of positional parameters.

trimVar :: forall a. Greediness -> Direction -> Term Var String -> Quoted Text -> Script (Term Var a)

Produces a Var that is a trimmed version of the input Var.

The Quoted Text is removed from the value of the Var, either from the beginning or from the end.

If the Quoted Text was produced by glob, it could match in multiple ways. You can choose whether to remove the shortest or the longest match.

The act of trimming a Var is assumed to be able to produce a new Var holding a different data type.

data Greediness

Constructors

ShortestMatch

LongestMatch

data Direction

Constructors

FromBeginning

FromEnd

data WithVar a

Allows modifying the value of a variable before it is passed to a command. The function is passed a Quoted Text which will expand to the value of the variable, and can modify it, by using eg mappend.

cmd "rmdir" (WithVar name ("/home/" <>))

Constructors

WithVar (Term Var a) (Quoted Text -> Quoted Text)

Instances

Param (WithVar a)

Allows modifying the value of a shell variable before it is passed to the command.

Defined in Control.Monad.Shell

Methods

toTextParam :: WithVar a -> Env -> Text

Monadic combinators

func :: (NameHinted namehint, CmdParams callfunc) => namehint -> Script () -> Script callfunc

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

The action is variadic; it can be passed any number of CmdParams. Typically, it will make sense to specify a more concrete type when defining the shell function.

The shell function will be given a unique name, that is not used by any other shell function. The namehint can be used to influence the contents of the function name, which makes for more readable generated shell code.

For example:

demo = script $ do
   hohoho <- mkHohoho
   hohoho (static 1)
   echo "And I heard him exclaim, ere he rode out of sight ..."
   hohoho (static 3)

mkHohoho :: Script (Term Val Int -> Script ())
mkHohoho = func (NamedLike "hohoho") $ do
   num <- takeParameter
   forCmd (cmd "seq" "1" num) $ \_n ->
      cmd "echo" "Ho, ho, ho!" "Merry xmas!"

forCmd :: forall a. Script () -> (Term Var a -> 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.

whileCmd :: Script () -> Script () -> Script ()

As long as the first Script exits nonzero, runs the second script.

ifCmd :: Script () -> Script () -> Script () -> Script ()

if with a Script conditional.

If the conditional exits 0, the first action is run, else the second.

whenCmd :: Script () -> Script () -> Script ()

when with a monadic conditional

unlessCmd :: Script () -> Script () -> Script ()

unless with a monadic conditional

caseOf :: forall a. Term Var a -> [(Quoted Text, Script ())] -> Script ()

Matches the value of the Var against the Quoted Text (which can be generated by glob), and runs the Script action associated with the first match.

arg <- takeParameter ()
caseOf arg
  [ (quote "-h", showHelp)
  , (glob "-*", cmd "echo" "Unknown option:" arg)
  ]

subshell :: Script () -> Script ()

Runs the script in a new subshell.

group :: Script () -> Script ()

Runs the script as a command group in the current subshell.

withEnv :: Param value => Text -> value -> Script () -> Script ()

Add a variable to the local environment of the script.

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

Pipes together two Scripts.

(-&&-) :: Script () -> Script () -> Script ()

ANDs two Scripts.

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

ORs two Scripts.

Redirection

class RedirFile r

Any function that takes a RedirFile can be passed a a FilePath, in which case the default file descriptor will be redirected to/from the FilePath.

Or, it can be passed a tuple of (Fd, FilePath), in which case the specified Fd will be redirected to/from the FilePath.

Minimal complete definition

fromRedirFile

Instances

RedirFile FilePath

Defined in Control.Monad.Shell

Methods

fromRedirFile :: Fd -> FilePath -> (Fd, FilePath)

RedirFile (Fd, FilePath)

Defined in Control.Monad.Shell

Methods

fromRedirFile :: Fd -> (Fd, FilePath) -> (Fd, FilePath)

(|>) :: RedirFile f => Script () -> f -> Script ()

Redirects to a file, overwriting any existing file.

For example, to shut up a noisy command:

cmd "find" "/" |> "/dev/null"

(|>>) :: RedirFile f => Script () -> f -> Script ()

Appends to a file. (If file doesn't exist, it will be created.)

(|<) :: RedirFile f => Script () -> f -> Script ()

Redirects standard input from a file.

toStderr :: Script () -> Script ()

Redirects a script's output to stderr.

(>&) :: (Script (), Fd) -> Fd -> Script ()

Redirects the first file descriptor to output to the second.

For example, to redirect a command's stderr to stdout:

cmd "foo" &stdError>&stdOutput

(<&) :: (Script (), Fd) -> Fd -> Script ()

Redirects the first file descriptor to input from the second.

For example, to read from Fd 42:

cmd "foo" &stdInput<&Fd 42

(&) :: Script () -> Fd -> (Script (), Fd)

Helper for >& and <&

hereDocument :: Script () -> Text -> Script ()

Provides the Text as input to the Script, using a here-document.

Error handling

stopOnFailure :: Bool -> Script ()

By default, shell scripts continue running past commands that exit nonzero. Use 'stopOnFailure True' to make the script stop on the first such command.

ignoreFailure :: Script () -> Script ()

Makes a nonzero exit status be ignored.

errUnlessVar :: Param param => forall a. Term Var a -> param -> Script (Term Var a)

Generates a new Var. If the input Var is empty then expanding this new Var will cause an error to be thrown, using the param as the error message. If the input Var is not empty, then the new Var expands to the same thing the input Var expands to.

Tests

test :: Test -> Script ()

Creates a Script that checks a Test and exits true (0) or false (1).

Useful with ifCmd, whenCmd, etc; for example:

ifCmd (test (FileExists "foo")) (foo, bar)

data Test where

Note that this should only include things that test(1) and shell built-in test commands support portably.

Constructors

TNot :: Test -> Test

TAnd :: Test -> Test -> Test

TOr :: Test -> Test -> Test

TEmpty :: Param p => p -> Test

TNonEmpty :: Param p => p -> Test

TStrEqual :: (Param p, Param q) => p -> q -> Test

TStrNotEqual :: (Param p, Param q) => p -> q -> Test

TEqual :: (Integral p, Integral q) => Term Var p -> Term Var q -> Test

TNotEqual :: (Integral p, Integral q) => Term Var p -> Term Var q -> Test

TGT :: (Integral p, Integral q) => Term Var p -> Term Var q -> Test

TLT :: (Integral p, Integral q) => Term Var p -> Term Var q -> Test

TGE :: (Integral p, Integral q) => Term Var p -> Term Var q -> Test

TLE :: (Integral p, Integral q) => Term Var p -> Term Var q -> Test

TFileEqual :: (Param p, Param q) => p -> q -> Test

TFileNewer :: (Param p, Param q) => p -> q -> Test

TFileOlder :: (Param p, Param q) => p -> q -> Test

TBlockExists :: Param p => p -> Test

TCharExists :: Param p => p -> Test

TDirExists :: Param p => p -> Test

TFileExists :: Param p => p -> Test

TRegularFileExists :: Param p => p -> Test

TSymlinkExists :: Param p => p -> Test

TFileNonEmpty :: Param p => p -> Test

TFileExecutable :: Param p => p -> Test

Shell Arithmetic Expressions

val :: Term t Integer -> Arith

Lifts a Term to Arith.

data Arith

This data type represents shell Arithmetic Expressions.

Note that in shell arithmetic, expressions that would evaluate to a Bool, such as ANot and AEqual instead evaluate to 1 for True and 0 for False.

Constructors

ANum Integer

AVar (Term Var Integer)

AStatic (Term Static Integer)

ANegate Arith

negation

APlus Arith Arith

+

AMinus Arith Arith

-

AMult Arith Arith

*

ADiv Arith Arith

/

AMod Arith Arith

mod

ANot Arith

not

AOr Arith Arith

or

AAnd Arith Arith

and

AEqual Arith Arith

==

ANotEqual Arith Arith

/=

ALT Arith Arith

<

AGT Arith Arith

>

ALE Arith Arith

<=

AGE Arith Arith

>=

ABitOr Arith Arith

OR of the bits of the two arguments

ABitXOr Arith Arith

XOR of the bits of the two arguments

ABitAnd Arith Arith

AND of the bits of the two arguments

AShiftLeft Arith Arith

shift left (first argument's bits are shifted by the value of the second argument)

AShiftRight Arith Arith

shift right

AIf Arith (Arith, Arith)

if the first argument is non-zero, the result is the second, else the result is the third

Instances

Enum Arith

Note that fromEnum, enumFromTo, and enumFromThenTo cannot be used with Arith.

Defined in Control.Monad.Shell

Methods

succ :: Arith -> Arith

pred :: Arith -> Arith

toEnum :: Int -> Arith

fromEnum :: Arith -> Int

enumFrom :: Arith -> [Arith]

enumFromThen :: Arith -> Arith -> [Arith]

enumFromTo :: Arith -> Arith -> [Arith]

enumFromThenTo :: Arith -> Arith -> Arith -> [Arith]

Num Arith

Arith is an instance of Num, which allows you to write expressions like this with shell variables, that generate Arithmetic Expressions.

val x * (100 + val y)

Defined in Control.Monad.Shell

Methods

(+) :: Arith -> Arith -> Arith

(-) :: Arith -> Arith -> Arith

(*) :: Arith -> Arith -> Arith

negate :: Arith -> Arith

abs :: Arith -> Arith

signum :: Arith -> Arith

fromInteger :: Integer -> Arith

Param Arith

Allows passing an Arithmetic Expression as a parameter.

Defined in Control.Monad.Shell

Methods

toTextParam :: Arith -> Env -> Text

Misc

comment :: Text -> Script ()

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

readVar :: Term Var String -> Script ()

Fills a variable with a line read from stdin.