Process library and s-expression based shell
Module Shexp_process
module Std : sig ... end
type 'a t

An 'a t value represent a process pipeline description, that can be evaluated using eval into a value of type 'a. Note that creating an 'a t value has no effect. Effects are only performed when calling eval.

module Context : sig ... end

Execution contexts

val eval : ?context:Context.t -> 'a t -> 'a

Evaluate the given process in the given environment.

If context is not specified, a temporary one is created. If you are calling eval many times, then creating a context and reusing it is more efficient.

module Logged : sig ... end
module Traced : sig ... end
module Prim : sig ... end
module type Debugger = sig ... end

shexp_process allows one to plug a debugger in the evaluator. Logged and Traced are essentially two non-interactive debuggers.

module With_debug (Dbg : Debugger) : sig ... end

Basic processes

val return : 'a -> 'a t

Classic monad operations. Note that because shexp_process uses threads under the hood, you should be careful about using global mutable data structures. To communicate values between concurrent processes, use the sync function.

val bind : 'a t -> f:( 'a -> 'b t ) -> 'b t
val map : 'a t -> f:( 'a -> 'b ) -> 'b t
val fail : exn -> _ t

Create a process that fails with the given exception. Evaluation of this process will raise this exception.

val fork : 'a t -> 'b t -> ('a * 'b) t

fork a b represents two processes that are executed concurrently. The resulting process will block until both a and b have finished and will return both of their results.

This is essentially the same as forking a system process: both process can independently change the current working directory, change their standard out, etc...

Regarding errors, if the evaluation of both processes fail, then only one the exceptions will be kept. It is not specified which one. You should use Traced to get a full trace and see what exceptions are raised and where.

val fork_unit : 'a t -> unit t -> 'a t

Same as map (fork a b) ~f:(fun (x, ()) -> x)

val fork_all : 'a t list -> 'a list t

fork_all ps represents List.length ps processes executed concurrently. fork_all generalizes fork from pairs of elements to lists of elements.

val fork_all_unit : unit t list -> unit t

A slightly more efficient version of map (fork_all ps) ~f:(fun _ -> ())

val protect : finally:unit t -> 'a t -> 'a t

protect ~finally t protects against execution errors. finally is always executed, even if the evaluation of t raises.

val reify_exn : ( 'a -> 'b t ) -> 'a -> 'b t

Capture exceptions into the process monad. You can use this if the argument of protect is the result of a function call.

For instance in the following code finally wouldn't be executed:

let f () = raise Not_found

             protect ~finally (f ())

You can write instead:

protect ~finally (reify_exn f ())

Running commands

val run : string -> string list -> unit t

Run an external program. This will fail if the external program does not exists, is signaled or exit with a non-zero exit code.

val run_exit_code : string -> string list -> int t

Run an external program and return its exit code. This will fail if the external program is signaled.

module Exit_status : sig ... end

Exit status of external processes

val run_exit_status : string -> string list -> Exit_status.t t

Run an external program and return its exit status.

val run_bool : ?true_v:int list -> ?false_v:int list -> string -> string list -> bool t

Run an external program, returns true if its exit code is part of true_v and false if it is part of false_v.

val call : string list -> unit t

Same functions as the 'run' ones above, but take a string list instead. This way, the first element and the others are treated in a homogeneous way. It can ease prepending commands in specific circumstances, e.g. if profile then call ("time" :: command) else call command

E.g. call ["grep"; "-i"; pattern; filename] is equivalent to run "grep" ["-i"; pattern; filename]

val call_exit_code : string list -> int t
val call_exit_status : string list -> Exit_status.t t
val call_bool : ?true_v:int list -> ?false_v:int list -> string list -> bool t
module Background_command : sig ... end
val spawn : string -> string list -> Background_command.t t

Start an external program but do not wait for its termination. If you never call wait on the result, the process will become a zombie after it terminates.

Wait for a background command to terminate and return its exit status.

Unix environment

val find_executable : string -> string option t

Return the absolute path to the given command.

val find_executable_exn : string -> string t
val get_env : string -> string option t

Return the value associated to the given environment variable.

val get_env_exn : string -> string t
val set_env : string -> string -> 'a t -> 'a t

set_env var value k represents the process k evaluated in a context where the envornment variable var is set to value.

val unset_env : string -> 'a t -> 'a t

set_env var value k represents the process k evaluated in a context where the environment variable var is unset.

Current working directory

val cwd_logical : string t

Return the current working directory. Note that there is no guarantee that this directory exists. For instance if a component in this path has is renamed during the evaluation of the process, then this will be a dangling directory.

val chdir : string -> 'a t -> 'a t

chdir dir k represents the process k evaluated in a context where the current working directory is changed to dir.


module Std_io : sig ... end
val echo : ?where:Std_io.t -> ?n:unit -> string -> unit t

Output a string on one of the standard io. ~n:() suppresses the newline output at the end.

val print : string -> unit t

echo ~where:Stdout

val eprint : string -> unit t

echo ~where:Stderr

val printf : ( 'a, unit, string, unit t ) format4 -> 'a
val eprintf : ( 'a, unit, string, unit t ) format4 -> 'a
val read_all : string t

Consume all standard input

val fold_lines : init:'a -> f:( 'a -> string -> 'a t ) -> 'a t

Fold over lines in the input. f is given the line with the end of line. Both "\r\n" and "\n" are treated as end of lines.

val fold_chunks : sep:char -> init:'a -> f:( 'a -> string -> 'a t ) -> 'a t

Fold over chunks separated by sep in the input. This can be used in conjunction with commands that support ending entries in the output with a '\000' such as find -print0.

val iter_lines : ( string -> unit t ) -> unit t
val iter_chunks : sep:char -> ( string -> unit t ) -> unit t


val pipe : ?connect:(Std_io.t list * Std_io.t) -> unit t -> 'a t -> 'a t

pipe ~connect:(aios, bio) a b is a process obtain by connecting the aios of a to the bio of b. a and b are evaluated in parallel (as with fork).

(aio, bio) defaults to ([Stdout], Stdin).

val pipe_both : ?connect:(Std_io.t list * Std_io.t) -> 'a t -> 'b t -> ('a * 'b) t

pipe_pair a b is a the same as pipe but returns the results of both a and b.

val epipe : unit t -> 'a t -> 'a t

Same as pipe ~connect:([Stderr], Stdin).

val epipe_both : 'a t -> 'b t -> ('a * 'b) t
val capture : Std_io.t list -> 'a t -> ('a * string) t

capture ios t = pipe_both ~connect:(ios, Stdin) read_all

val capture_unit : Std_io.t list -> unit t -> string t

capture_unit ios t = pipe ~connect:(ios, Stdin) read_all


val redirect : Std_io.t list -> ?perm:int -> flags:Unix.open_flag list -> string -> 'a t -> 'a t

redirect ios ?perm ~flags filename t redirects the following ios to a file in t. perm and flags are passed the same as for Unix.openfile.

val stdout_to : ?append:unit -> string -> 'a t -> 'a t

Convenient wrappers for redirect

val stderr_to : ?append:unit -> string -> 'a t -> 'a t
val outputs_to : ?append:unit -> string -> 'a t -> 'a t
val stdin_from : string -> 'a t -> 'a t
val replace_io : ?stdin:Std_io.t -> ?stdout:Std_io.t -> ?stderr:Std_io.t -> 'a t -> 'a t

Replace the given standard io by the given one. For instance to redirect stdout to stderr: replace_io ~stdout:Stderr t

val out_to_err : 'a t -> 'a t

out_to_err t = replace_io ~stdout:Stderr t

val err_to_out : 'a t -> 'a t

err_to_out t = replace_io ~stderr:Stdout t

Temporary files & directory

val temp_dir : string t

Return the current temporary directory

val set_temp_dir : string -> 'a t -> 'a t

set_temp_dir dir k represents the process k evaluated in a context where the current temporary directory is set to dir.

val with_temp_file : prefix:string -> suffix:string -> ( string -> 'a t ) -> 'a t

with_temp_file ~prefix ~suffix f is a process that creates a temporary file and passes it to f. The file is created inside the temporary directory.

When the process returned by f finishes, the file is removed.

val with_temp_dir : prefix:string -> suffix:string -> ( string -> 'a t ) -> 'a t

Same as with_temp_file but creates a directory. The directory and its contents are deleted when the process finishes.

FS operations

val chmod : string -> perm:Unix.file_perm -> unit t
val chown : string -> uid:int -> gid:int -> unit t
val mkdir : ?perm:Unix.file_perm -> ?p:unit -> string -> unit t
val rm : string -> unit t
val rmdir : string -> unit t
val mkfifo : ?perm:Unix.file_perm -> string -> unit t
val rename : string -> string -> unit t
val stat : string -> Unix.LargeFile.stats t
val lstat : string -> Unix.LargeFile.stats t
val readdir : string -> string list t
val file_exists : string -> bool t
val rm_rf : string -> unit t

Recursively remove a tree


val sleep : float -> unit t


val new_channel : 'a t
val sync : 'a Event.event -> 'a t


module Infix : sig ... end
module Let_syntax : sig ... end

Open this module when using ppx_let

module List : sig ... end