turtle

Turtle is a reimplementation of the Unix command line environment in Haskell so that you can use Haskell as a scripting language or a shell. Think of turtle as coreutils embedded within the Haskell language.

Quick start

• Install Stack

$ stack ghci turtle
Prelude> :set -XOverloadedStrings
Prelude> import Turtle

... and try out some basic filesystem operations:

Prelude Turtle> cd "/tmp"
Prelude Turtle> mkdir "test"
Prelude Turtle> touch "test/foo"
Prelude Turtle> testfile "test/foo"
True
Prelude Turtle> rm "test/foo"
Prelude Turtle> testfile "test/foo"
False
Prelude Turtle> rmdir "test"
Prelude Turtle> view (lstree "/usr/lib")
FilePath "/usr/lib/gnome-screensaver"
FilePath "/usr/lib/gnome-screensaver/gnome-screensaver-dialog"
FilePath "/usr/lib/libplist.so.1.1.8"
FilePath "/usr/lib/tracker"
FilePath "/usr/lib/tracker/tracker-miner-fs"
FilePath "/usr/lib/tracker/tracker-extract"
FilePath "/usr/lib/tracker/tracker-writeback"
FilePath "/usr/lib/tracker/tracker-search-bar"
FilePath "/usr/lib/tracker/tracker-store"
FilePath "/usr/lib/libgif.so.4.1"
...

To learn more, read the turtle tutorial.

Goals

The turtle library focuses on being a "better Bash" by providing a typed and light-weight shell scripting experience embedded within the Haskell language. If you have a large shell script that is difficult to maintain, consider translating it to a "turtle script" (i.e. a Haskell script using the turtle library).

Among typed languages, Haskell possesses a unique combination of features that greatly assist scripting:

• Haskell has global type inference, so all type annotations are optional
• Haskell is functional and not object-oriented, so boilerplate is minimal
• Haskell can be type-checked and interpreted quickly (< 1 second startup time)

Features

• Batteries included: Command an extended suite of predefined utilities

• Interoperability: You can still run external shell commands

• Portability: Works on Windows, OS X, and Linux

• Exception safety: Safely acquire and release resources

• Streaming: Transform or fold command output in constant space

• Patterns: Use typed regular expressions that can parse structured values

• Formatting: Type-safe printf-style text formatting

• Modern: Supports text and system-filepath

Caveats

Unlike shelly, this package does not use a monad transformer to keep track of state like the current working directory or environment variables. Instead, all state changes are made to the process's global state.

Development Status

turtle's types and idioms are reasonably complete and I don't expect there to be significant changes to the library's core API. The only major functionality that I might add in the future would be to wrap optparse-applicative in a simpler API.

The set of available tools currently covers as many filesystem utilities as I could find across Hackage, but I would like to continue to add to the set of available tools to minimally match coreutils.

Community Resources

• The haskell-turtle tag on Stack Overflow

How to contribute

• Contribute more utilities

• Write turtle tutorials

License (BSD 3-clause)

Copyright (c) 2017 Gabriella Gonzalez
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
• Neither the name of Gabriella Gonzalez nor the names of other contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.