# Module Sys

    module Sys: sig .. end

System interface.

Every function in this module raises `Sys_error` with an informative message when the underlying system call signal an error.

    val argv : string array

The command line arguments given to the process. The first element is the command name used to invoke the program. The following elements are the command-line arguments given to the program.

    val executable_name : string

The name of the file containing the executable currently running. This name may be absolute or relative to the current directory, depending on the platform and whether the program was compiled to bytecode or a native executable.

    val file_exists : string -> bool

Test if a file with the given name exists.

    val is_directory : string -> bool

Returns `true` if the given name refers to a directory, `false` if it refers to another kind of file. Raise `Sys_error` if no file exists with the given name.

- Since 3.10.0

    val remove : string -> unit

Remove the given file name from the file system.

    val rename : string -> string -> unit

Rename a file. `rename oldpath newpath` renames the file called `oldpath`, giving it `newpath` as its new name, moving it between directories if needed. If `newpath` already exists, its contents will be replaced with those of `oldpath`. Depending on the operating system, the metadata (permissions, owner, etc) of `newpath` can either be preserved or be replaced by those of `oldpath`.

- Since 4.06 concerning the "replace existing file" behavior

    val getenv : string -> string

Return the value associated to a variable in the process environment. Raise `Not_found` if the variable is unbound.

    val getenv_opt : string -> string option

Return the value associated to a variable in the process environment or `None` if the variable is unbound.

- Since 4.05

    val command : string -> int

Execute the given shell command and return its exit code.

    val time : unit -> float

Return the processor time, in seconds, used by the program since the beginning of execution.

    val chdir : string -> unit

Change the current working directory of the process.

    val getcwd : unit -> string

Return the current working directory of the process.

    val readdir : string -> string array

Return the names of all files present in the given directory. Names denoting the current directory and the parent directory (`"."` and `".."` in Unix) are not returned. Each string in the result is a file name rather than a complete path. There is no guarantee that the name strings in the resulting array will appear in any specific order; they are not, in particular, guaranteed to appear in alphabetical order.

    val interactive : bool ref

This reference is initially set to `false` in standalone programs and to `true` if the code is being executed under the interactive toplevel system `ocaml`.

    val os_type : string

Operating system currently executing the OCaml program. One of

- `"Unix"` (for all Unix versions, including Linux and Mac OS X),
- `"Win32"` (for MS-Windows, OCaml compiled with MSVC++ or Mingw),
- `"Cygwin"` (for MS-Windows, OCaml compiled with Cygwin).

    type backend_type =

`|` | `Native`
`|` | `Bytecode`
`|` | `Other of `string``

Currently, the official distribution only supports `Native` and `Bytecode`, but it can be other backends with alternative compilers, for example, javascript.

- Since 4.04.0

    val backend_type : backend_type

Backend type currently executing the OCaml program.

- Since 4.04.0

    val unix : bool

True if `Sys.os_type = "Unix"`.

- Since 4.01.0

    val win32 : bool

True if `Sys.os_type = "Win32"`.

- Since 4.01.0

    val cygwin : bool

True if `Sys.os_type = "Cygwin"`.

- Since 4.01.0

    val word_size : int

Size of one word on the machine currently executing the OCaml program, in bits: 32 or 64.

    val int_size : int

Size of `int`, in bits. It is 31 (resp. 63) when using OCaml on a 32-bit (resp. 64-bit) platform. It may differ for other implementations, e.g. it can be 32 bits when compiling to JavaScript.

- Since 4.03.0

    val big_endian : bool

Whether the machine currently executing the Caml program is big-endian.

- Since 4.00.0

    val max_string_length : int

Maximum length of strings and byte sequences.

    val max_array_length : int

Maximum length of a normal array (i.e. any array whose elements are not of type `float`). The maximum length of a `float array` is `max_floatarray_length` if OCaml was configured with `--enable-flat-float-array` and `max_array_length` if configured with `--disable-flat-float-array`.

    val max_floatarray_length : int

Maximum length of a floatarray. This is also the maximum length of a `float array` when OCaml is configured with `--enable-flat-float-array`.

    val runtime_variant : unit -> string

Return the name of the runtime variant the program is running on. This is normally the argument given to `-runtime-variant` at compile time, but for byte-code it can be changed after compilation.

- Since 4.03.0

    val runtime_parameters : unit -> string

Return the value of the runtime parameters, in the same format as the contents of the `OCAMLRUNPARAM` environment variable.

- Since 4.03.0

## Signal handling

    type signal_behavior =

`|` | `Signal_default`
`|` | `Signal_ignore`
`|` | `Signal_handle of `(int -> unit)``

What to do when receiving a signal:

- `Signal_default`: take the default behavior (usually: abort the program)
- `Signal_ignore`: ignore the signal
- `Signal_handle f`: call function `f`, giving it the signal number as argument.

    val signal : int -> signal_behavior -> signal_behavior

Set the behavior of the system on receipt of a given signal. The first argument is the signal number. Return the behavior previously associated with the signal. If the signal number is invalid (or not available on your system), an `Invalid_argument` exception is raised.

    val set_signal : int -> signal_behavior -> unit

Same as `Sys.signal` but return value is ignored.

### Signal numbers for the standard POSIX signals.

    val sigabrt : int

Abnormal termination

    val sigalrm : int

Timeout

    val sigfpe : int

Arithmetic exception

    val sighup : int

Hangup on controlling terminal

    val sigill : int

Invalid hardware instruction

    val sigint : int

Interactive interrupt (ctrl-C)

    val sigkill : int

Termination (cannot be ignored)

    val sigpipe : int

Broken pipe

    val sigquit : int

Interactive termination

    val sigsegv : int

Invalid memory reference

    val sigterm : int

Termination

    val sigusr1 : int

Application-defined signal 1

    val sigusr2 : int

Application-defined signal 2

    val sigchld : int

Child process terminated

    val sigcont : int

Continue

    val sigstop : int

Stop

    val sigtstp : int

Interactive stop

    val sigttin : int

Terminal read from background process

    val sigttou : int

Terminal write from background process

    val sigvtalrm : int

Timeout in virtual time

    val sigprof : int

Profiling interrupt

    val sigbus : int

Bus error

- Since 4.03

    val sigpoll : int

Pollable event

- Since 4.03

    val sigsys : int

Bad argument to routine

- Since 4.03

    val sigtrap : int

Trace/breakpoint trap

- Since 4.03

    val sigurg : int

Urgent condition on socket

- Since 4.03

    val sigxcpu : int

Timeout in cpu time

- Since 4.03

    val sigxfsz : int

File size limit exceeded

- Since 4.03

    exception Break

Exception raised on interactive interrupt if `Sys.catch_break` is on.

    val catch_break : bool -> unit

`catch_break` governs whether interactive interrupt (ctrl-C) terminates the program or raises the `Break` exception. Call `catch_break true` to enable raising `Break`, and `catch_break false` to let the system terminate the program on user interrupt.

    val ocaml_version : string

`ocaml_version` is the version of OCaml. It is a string of the form `"major.minor[.patchlevel][+additional-info]"`, where `major`, `minor`, and `patchlevel` are integers, and `additional-info` is an arbitrary string. The `[.patchlevel]` and `[+additional-info]` parts may be absent.

    val enable_runtime_warnings : bool -> unit

Control whether the OCaml runtime system can emit warnings on stderr. Currently, the only supported warning is triggered when a channel created by `open_*` functions is finalized without being closed. Runtime warnings are enabled by default.

- Since 4.03.0

    val runtime_warnings_enabled : unit -> bool

Return whether runtime warnings are currently enabled.

- Since 4.03.0

## Optimization

    val opaque_identity : 'a -> 'a

For the purposes of optimization, `opaque_identity` behaves like an unknown (and thus possibly side-effecting) function.

At runtime, `opaque_identity` disappears altogether.

A typical use of this function is to prevent pure computations from being optimized away in benchmarking loops. For example:

          for _round = 1 to 100_000 do
            ignore (Sys.opaque_identity (my_pure_computation ()))
          done

- Since 4.03.0