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Genspio: Generate Shell Phrases In OCaml

Genspio is a typed EDSL to generate shell scripts and commands from OCaml.

The idea is to build values of type 'a EDSL.t with the combinators in the Genspio.EDSL module, and compile them to POSIX shell scripts (or one-liners) with functions from Genspio.Compile. See the file src/examples/small.ml which generates a useful list of usage examples, or the section “Getting Started” below.

The tests run the output of the compiler against a few shells that it tries to find on the host (e.g. dash, bash, busybox, mksh, zsh … cf. the example test results summary below).

If you have any questions, do not hesitate to submit an issue.

Genspio's documentation root is at https://smondet.gitlab.io/genspio-doc/.


You can install the library though opam:

opam install genspio

Or get the development version with opam pin:

opam pin add genspio https://github.com/hammerlab/genspio.git

You can also build locally:

You need OCaml ≥ 4.03.0 together with nonstd, sosa, and jbuilder:

ocaml please.mlt configure
jbuilder build @install

Getting Started

Here is a quick example:

utop> open Genspio.EDSL;;

let c =
  let username_one_way : c_string t =
    (* We lift the string "USER" to EDSL-land and use function `getenv`: *)
    getenv (string "USER") in
  let username_the_other_way : c_string t =
    (* The usual pipe operator is `||>` *)
    (exec ["whoami"] ||> exec ["tr"; "-d"; "\\n"])
    (* `get_stdout` takes `stdout` from a `unit t` as a `byte_array t` *)
    |> get_stdout
    (* `to_c_string` checks that a `byte_array t` can be casted to a `c_string` *)
    |> to_c_string 
  let my_printf : string -> c_string t list -> unit t = fun fmt args ->
    (* The function `call` is like `exec` but operates on `c_string t` values
       instead of just OCaml strings: *)
    call (string "printf" :: string fmt :: args) in
  (* The operator `=$=` is `string t` equality, it returns a `bool t` that
     we can use with `if_seq`: *)
  if_seq (username_one_way =$= username_the_other_way)
        my_printf "Username matches: `%s`\\n" [username_one_way];
        my_printf "Usernames do not match: `%s` Vs `%s`\\n"
          [username_one_way; username_the_other_way];
val c : unit t

utop> Sys.command (Genspio.Compile.to_one_liner c);;
Username matches: `smondet`
- : int = 0

More examples:

  • There are many examples in src/examples/small.ml which are used to generate the usage examples documentation webpage.
  • The file src/examples/downloader.ml contains a (much) bigger example.
  • The file src/examples/vm_tester.ml is a “Makefile + scripts” generator to setup Qemu virtual machines, they can be for instance used to run the tests on more exotic platforms.
  • The project hammerlab/secotrec is a real-world, larger-scale use of Genspio (for now using version 0.0.0).


To run the tests you also need make and there is an additional dependency on the uri library, see:

jbuilder build $genspio_test
$genspio_test --help

Try this:

$genspio_test --important-shells bash,dash /tmp/gtests/
cd /tmp/gtests/
make run-all # Attempts to run all the tests on all the shells
make check   # Checks that all the tests for the important ones succeeded

You can generate a markdown report with make report and check report.md.

Some failures are expected with not-really-POSIX or buggy shells like KSH93, or on some corner cases cf. #35.

You can check failures in the <shell-test>/failures.md files, see for instance ksh-StdML/failures.md for the failures of the “KSH with standard Genspio compilation to multi-line scripts” (similarly there are <shell-test>/successes.md files).

Additional Documentation

From here, one can explore:

  • Some implementation notes.
  • More information on testing, e.g. on more exotic operating systems.


It's Apache 2.0.