HSH-2.1.0: Library to mix shell scripting with Haskell programs

MaintainerJohn Goerzen <jgoerzen@complete.org>
Safe HaskellNone



Copyright (c) 2006 John Goerzen, jgoerzen@complete.org

Welcome to HSH, the Haskell Shell infrastructure.


HSH is designed to let you mix and match shell expressions with Haskell programs.

Here are a few examples to get you started:

run $ "echo /etc/pass*" :: IO String
 -> "/etc/passwd /etc/passwd-"

runIO $ "ls -l" -|- "wc -l"
 -> 12

runIO $ "ls -l" -|- wcL
 -> 12

runIO $ ("ls", ["-l", "file with spaces.txt"])
glob "~jgoerzen" >>= cd . head

wcL is a pure Haskell function defined in HSH.ShellEquivs.wcL as:

wcL :: [String] -> [String]
wcL inp = [show $ genericLength inp]

Here's another example:

 let countLines = (zipWith (\i line -> printf "%-5d %s" i line) 
      [(1::Int)..])::([String] -> [String])

 runIO $ ("ls", ["-l"]) -|- countLines -|- filter (isSuffixOf "hs")
   6     -rw-r--r-- 1 jgoerzen jgoerzen  1285 Jun  6 09:43 HSH.hs
   11    -rw-r--r-- 1 jgoerzen jgoerzen   565 Jun  6 09:43 test.hs

To use HSH, you'll just want to import the HSH module. To learn more, please see the information in HSH.Command and HSH.ShellEquivs.

You can run a command with HSH in several ways:

  • By using run in a context that expects IO (), which will leave the final standard output going to the normal standard output of the program
  • By using run in a context that expects a String, which will capture standard output into a buffer and present it as a String
  • Any of the numerous other methods documented in RunResult.
  • The shortcut functions runIO and runSL. runIO lets you run a command and force the context IO (), which is a frequently-useful shortcut when you don't care about the result. runSL grabs the first line of output in the result.

You can then specify a command, which could be a single command or a command joined together with pipes.

There are many different items that make valid types; see the list of instances of ShellCommand for a full list. Here are a few:

  • A simple bare string is passed to the shell for execution. The shell will then typically expand wildcards, parse parameters, etc.
  • A (String, [String]) tuple. The first item in the tuple gives the name of a program to run, and the second gives its arguments. The shell is never involved. This is ideal for passing filenames, since there is no security risk involving special shell characters.
  • A Haskell function. This function will accept input representing its standard input and generate output to go to stdout. Function types that are supported natively include (String -> String), (String -> IO String), plus many more involving ByteStrings and functions that take no input. See ShellCommand for more.

Pipes can be constructed by using the -|- operator, as illustrated above. It is quite possible to pipe data between Haskell functions and shell commands at will.

In addition, HSH.ShellEquivs provides a number of useful pure-Haskell equivalents of regular shell commands.

For more information, please consult the other modules in HSH as well as the HSH wiki at: