Shh
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Shh is a library to enable convinient shell-like programming in Haskell.
It works well in scripts, and from GHCi, allowing you to use GHCi as a shell.
It supports
-
Automatically defining a function for each executable on your $PATH
using template Haskell, as well as a runtime check to ensure they all
exist on startup.
-
Redirction of stdout and stderr
-- Redirect stdout
λ echo "Hello" &> StdErr
λ echo "Hello" &> Truncate ".tmp_file"
-- Redirect stderr
λ echo "Hello" &!> Append "/dev/null"
λ echo "Hello" &!> StdOut
-
Piping stdout or stderr to the input of a chained process
λ cat "/dev/urandom" |> xxd |> head "-n" 5
-
Multiple processes sequentially feeding a single process
λ (echo 1 >> echo 2) |> cat
-
Use of Haskells concurrency primitives.
λ race (sleep 1) $ curl "http://this_needs_to_timeout_after_1_second"
λ d <- readTrim $ mktemp "-d"
λ :{
| System.Directory.withCurrentDirectory d $ do
| mapConcurrently_ (curl "-LOJs")
| [ "https://raw.githubusercontent.com/luke-clifton/shh/master/shell.nix"
| , "https://raw.githubusercontent.com/luke-clifton/shh/master/shh.cabal"
| ]
| ls
| :}
-
Capturing of process output
λ loggedIn <- nub . words <$> readProc users
λ putStrLn $ "Logged in users: " ++ show loggedIn
λ mapM_ putStrLn =<< readSplit0 (Shh.Example.find "-maxdepth" 1 "-print0")
-
Capturing infinite output of a process lazily
λ withRead (cat "/dev/urandom" |> xxd) $ mapM_ putStrLn . take 3 . lines
00000000: 8fcb ebee 9228 a897 3bfc 1d05 491d aceb .....(..;...I...
00000010: 47de 3ea3 2788 44ac 9b85 0a0f a458 b949 G.>.'.D......X.I
00000020: 5308 ddfe 5790 5a5f 39e3 bbb6 b689 2b03 S...W.Z_9.....+.
-
Write strings to stdin of a process.
λ writeProc cat "Hello\n"
Hello
λ "Hello" >>> shasum
f7ff9e8b7bb2e09b70935a5d785e0cc5d9d0abf0 -
λ shasum <<< "Hello"
f7ff9e8b7bb2e09b70935a5d785e0cc5d9d0abf0 -
-
Proper exceptions, when a process exits with a failure code, an exception
is thrown. You can catch these normally. The exception includes the error
code, the command, and all it's arguments.
λ false "Ha, it died"
*** Exception: Command `false "Ha, it died"` failed [exit 1]
λ catchCode false
1
Mnemonics
Shh has many symbols that might seem intimidating at first, but there
is a simple mnemonic for them.
| Piping. Looks like a pipe, same as in POSIX shells.
& Redirection, think of the shell `2>&1`
>,< The direction of flow of a command
! Operate on stderr instead of stdout
So, for example,
ls |> cat Pipe the stdout of `ls` into stdin of `cat`
cat <| ls Same as above
ls &> StdErr Redirect stdout of `ls` to wherever stderr is going.
StdErr <& ls Same as above
ls &!> StdOut Redirect stderr of `ls` to wherever stdout is going.
StdOut <!& ls Same as above
Usage
Enable Temlpate Haskell and load the environment
{-# LANGUAGE TemplateHaskell #-}
$(loadEnv)
You now have all your executables available as simple to read
Haskell functions.
If you want to check that all the dependenies still exist, you can use
missingExecutables :: IO [String]
, which will tell you if anything is
missing.
Usage in GHCi
If you want ^D
to be recognised as a EOF marker (when running commands
that read from stdin) when running in GHCi, you will need to run the
initInteractive
function. This sets the line buffering appropriately and
ensures the terminal is in canonical mode.
Script Usage
TODO: Fill this in once on Hackage.