Control.Monad.Shell

This is a shell monad, for generating shell scripts.

Core

data Script a

Shell script monad.

Instances

Monad Script

Functor Script

(~) * f () => CmdParams (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 Var a

A shell variable, with an associated phantom type.

Instances

Param (Var a)

data Quoted a

A value that is safely quoted.

Instances

Eq a => Eq (Quoted a)

Ord a => Ord (Quoted a)

Show a => Show (Quoted a)

Monoid a => Monoid (Quoted a)

Param (Quoted Text)

Quoted Text arguments are passed as-is.

quote :: Text -> Quoted Text

Quotes the Text 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.

glob :: Text -> Quoted Text

Treats the Text as a glob, which expands to one parameter per matching file.

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 "name"
  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.

Param Text

Text arguments are automatically quoted.

Param Arith

Allows passing an Arithmetic Expression as a parameter.

Param Output

Allows passing the output of a command as a parameter.

Param (WithVar a)

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

Show v => Param (Val v)

Any value that can be shown can be passed to cmd; just wrap it inside a Val.

Param (Quoted Text)

Quoted Text arguments are passed as-is.

Param (Var a)

class CmdParams t

Allows a function to take any number of Params.

Minimal complete definition

cmdAll

Instances

(~) * f () => CmdParams (Script f)

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

newtype Val v

An arbitrary value.

Constructors

Val v

Instances

Show v => Param (Val v)

Any value that can be shown can be passed to cmd; just wrap it inside a Val.

Shell variables

newtype NamedLike

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

Constructors

NamedLike Text

Instances

NameHinted NamedLike

class NameHinted h

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

To skip providing a hint, use '()'. To provide a hint, use '(NamedLike "name")'.

Minimal complete definition

hinted

Instances

NameHinted ()

NameHinted NamedLike

NameHinted (Maybe Text)

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

newVarContaining :: NameHinted namehint => forall a. Text -> namehint -> Script (Var a)

Creates a new shell variable, with an initial value.

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

Sets the Var to the value of the param.

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

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

positionalParameters :: forall a. 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 (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. Var a -> param -> Script (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. Var a -> param -> Script (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. Var a -> Script (Var Int)

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 -> Var String -> Quoted Text -> Script (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 (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.

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 (Val 1)
   echo "And I heard him exclaim, ere he rode out of sight ..."
   hohoho (Val 3)

mkHohoho :: Script (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 () -> (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 monadic 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. 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.

(-|-) :: 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

RedirFile (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. Var a -> param -> Script (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.

Shell Arithmetic Expressions

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 (Var 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

ACond Arith Arith Arith

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

Instances

Param Arith

Allows passing an Arithmetic Expression as a parameter.

Misc

comment :: Text -> Script ()

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

readVar :: Var String -> Script ()

Generates shell code to fill a variable with a line read from stdin.