Portability	portable
Stability	provisional
Maintainer	John Goerzen <jgoerzen@complete.org>

HSH.Command

Description

Synopsis

Documentation

class Show a => ShellCommand a whereSource

A shell command is something we can invoke, pipe to, pipe from, or pipe in both directions. All commands that can be run as shell commands must define these methods.

Minimum implementation is fdInvoke.

Methods

fdInvoke Source

Arguments

:: a	The command
-> Fd	fd to pass to it as stdin
-> Fd	fd to pass to it as stdout
-> [Fd]	Fds to close in the child. Will not harm Fds this child needs for stdin and stdout.
-> IO ()	Action to run post-fork in child (or in main process if it doesn't fork)
-> IO [InvokeResult]	Returns an action that, when evaluated, waits for the process to finish and returns an exit code.

Invoke a command.

Instances

ShellCommand String	An instance of `ShellCommand` for an external command. The String is split using words to the command to run, and the arguments, if any.
ShellCommand ([String] -> [String])	An instance of `ShellCommand` for a pure Haskell function mapping [String] to [String]. A [String] is generated from a Handle via the `lines` function, and the reverse occurs via `unlines`. So, this function is intended to operate upon lines of input and produce lines of output.
ShellCommand ([String] -> IO [String])	The same for an IO function
ShellCommand (String -> IO String)
ShellCommand (String -> String)	An instance of `ShellCommand` for a pure Haskell function mapping String to String. Implement in terms of (String -> IO String) for simplicity.
ShellCommand (ByteString -> IO ByteString)
ShellCommand (ByteString -> ByteString)
ShellCommand (ByteString -> IO ByteString)
ShellCommand (ByteString -> ByteString)
ShellCommand (String, [String])	An instance of `ShellCommand` for an external command. The first String is the command to run, and the list of Strings represents the arguments to the program, if any.
(ShellCommand a, ShellCommand b) => ShellCommand (PipeCommand a b)	An instance of `ShellCommand` represeting a pipeline.

data (ShellCommand a, ShellCommand b) => PipeCommand a b Source

Constructors

PipeCommand a b

Instances

(ShellCommand a, ShellCommand b) => Show (PipeCommand a b)
(ShellCommand a, ShellCommand b) => ShellCommand (PipeCommand a b)	An instance of `ShellCommand` represeting a pipeline.

(-|-) :: (ShellCommand a, ShellCommand b) => a -> b -> PipeCommand a bSource

Pipe the output of the first command into the input of the second.

class RunResult a whereSource

Different ways to get data from run.

IO () runs, throws an exception on error, and sends stdout to stdout
IO String runs, throws an exception on error, reads stdout into a buffer, and returns it as a string. Note: This output is not lazy.
IO [String] is same as IO String, but returns the results as lines. Note: this output is not lazy.
IO ProcessStatus runs and returns a ProcessStatus with the exit information. stdout is sent to stdout. Exceptions are not thrown.
IO (String, ProcessStatus) is like IO ProcessStatus, but also includes a description of the last command in the pipe to have an error (or the last command, if there was no error)
IO ByteString and IO (ByteString, ProcessStatus) are similar to their String counterparts.
IO Int returns the exit code from a program directly. If a signal caused the command to be reaped, returns 128 + SIGNUM.
IO Bool returns True if the program exited normally (exit code 0, not stopped by a signal) and False otherwise.

To address insufficient laziness, you can process anything that needs to be processed lazily within the pipeline itself.

Methods

run :: ShellCommand b => b -> aSource

Runs a command (or pipe of commands), with results presented in any number of different ways.

Instances

RunResult (IO Bool)
RunResult (IO Int)
RunResult (IO [String])
RunResult (IO String)
RunResult (IO ())
RunResult (IO (String, ProcessStatus))
RunResult (IO ByteString)
RunResult (IO ByteString)
RunResult (IO ProcessStatus)

runIO :: ShellCommand a => a -> IO ()Source

A convenience function. Refers only to the version of run that returns IO (). This prevents you from having to cast to it all the time when you do not care about the result of run.

The implementation is simply:

runIO :: (ShellCommand a) => a -> IO ()
runIO = run

runSL :: ShellCommand a => a -> IO String Source

Another convenience function. This returns the first line of the output, with any trailing newlines or whitespace stripped off. No leading whitespace is stripped. This function will raise an exception if there is not at least one line of output. Mnemonic: runSL means "run single line".

This command exists separately from run because there is already a run instance that returns a String, though that instance returns the entirety of the output in that String.

type InvokeResult = (String, IO ProcessStatus)Source

Result type for shell commands. The String is the text description of the command, not its output.

tryEC :: IO a -> IO (Either ProcessStatus a)Source

Handle an exception derived from a program exiting abnormally

catchEC :: IO a -> (ProcessStatus -> IO a) -> IO aSource

Catch an exception derived from a program exiting abnormally