# 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.

- Since 3.10
- Raises `Sys_error` if no file exists with the given name.

    val is_regular_file : string -> bool

Returns `true` if the given name refers to a regular file, `false` if it refers to another kind of file.

- Since 5.1
- Raises `Sys_error` if no file exists with the given name.

    val remove : string -> unit

Remove the given file name from the file system.

    val rename : string -> string -> unit

Rename a file or directory. `rename oldpath newpath` renames the file or directory called `oldpath`, giving it `newpath` as its new name, moving it between (parent) directories if needed. If a file named `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.

- Raises `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.

The argument of `Sys.command` is generally the name of a command followed by zero, one or several arguments, separated by whitespace. The given argument is interpreted by a shell: either the Windows shell `cmd.exe` for the Win32 ports of OCaml, or the POSIX shell `sh` for other ports. It can contain shell builtin commands such as `echo`, and also special characters such as file redirections `>` and `<`, which will be honored by the shell.

Conversely, whitespace or special shell characters occurring in command names or in their arguments must be quoted or escaped so that the shell does not interpret them. The quoting rules vary between the POSIX shell and the Windows shell. The `Filename.quote_command` performs the appropriate quoting given a command name, a list of arguments, and optional file redirections.

    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 mkdir : string -> int -> unit

Create a directory with the given permissions.

- Since 4.12

    val rmdir : string -> unit

Remove an empty directory.

- Since 4.12

    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 io_buffer_size : int

Size of C buffers used by the runtime system and IO primitives of the `unix` library.

Primitives that read from or write to values of type `string` or `bytes` generally use an intermediate buffer of this size to avoid holding the domain lock.

- Since 5.4

    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`.

- Alert unsynchronized_access. The interactive status is a mutable global state.

    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-w64),
- `"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

    val backend_type : backend_type

Backend type currently executing the OCaml program.

- Since 4.04

    val unix : bool

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

- Since 4.01

    val win32 : bool

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

- Since 4.01

    val cygwin : bool

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

- Since 4.01

    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

    val big_endian : bool

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

- Since 4.00

    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

    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

    val poll_actions : unit -> unit

Run any pending runtime actions, such as minor collections, major GC slices, signal handlers, finalizers, or memprof callbacks.

- Since 5.3

## Signal handling

    type signal = int

The type for signal numbers.

Negative numbers are used by OCaml to provide a platform-independent number for signals recognised by OCaml. Positive numbers are always the platform-dependent value for a given signal. The function `Sys.signal_of_int` converts known platform-dependent numbers to independent ones, and `Sys.signal_to_int` does the reverse.

- Since 5.4

    type signal_behavior =

`|` | `Signal_default`
`|` | `Signal_ignore`
`|` | `Signal_handle of `(signal -> 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 an argument.

    val signal : signal -> 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.

If a platform-dependent signal number is used, it will be converted to a platform-independent signal using `Sys.signal_of_int` before calling the handler.

    val set_signal : signal -> signal_behavior -> unit

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

### Signal numbers for the standard POSIX signals.

    val sigabrt : signal

Abnormal termination

    val sigalrm : signal

Timeout

    val sigfpe : signal

Arithmetic exception

    val sighup : signal

Hangup on controlling terminal

    val sigill : signal

Invalid hardware instruction

    val sigint : signal

Interactive interrupt (ctrl-C)

    val sigkill : signal

Termination (cannot be ignored)

    val sigpipe : signal

Broken pipe

    val sigquit : signal

Interactive termination

    val sigsegv : signal

Invalid memory reference

    val sigterm : signal

Termination

    val sigusr1 : signal

Application-defined signal 1

    val sigusr2 : signal

Application-defined signal 2

    val sigchld : signal

Child process terminated

    val sigcont : signal

Continue

    val sigstop : signal

Stop (cannot be caught or ignored)

    val sigtstp : signal

Interactive stop

    val sigttin : signal

Terminal read from background process

    val sigttou : signal

Terminal write from background process

    val sigvtalrm : signal

Timeout in virtual time

    val sigprof : signal

Profiling interrupt

    val sigbus : signal

Bus error

- Since 4.03

    val sigpoll : signal

Pollable event

- Since 4.03

    val sigsys : signal

Bad argument to routine

- Since 4.03

    val sigtrap : signal

Trace/breakpoint trap

- Since 4.03

    val sigurg : signal

Urgent condition on socket

- Since 4.03

    val sigxcpu : signal

Timeout in cpu time

- Since 4.03

    val sigxfsz : signal

File size limit exceeded

- Since 4.03

    val sigio : signal

I/O is possible on a descriptor

- Since 5.4

    val sigwinch : signal

Window size change

- Since 5.4

    val signal_to_string : signal -> string

`signal_to_string` formats an OCaml `signal` as a C POSIX constant or `"SIG(%d)"` for platform-dependent signal numbers.

- Since 5.4
- Raises `Invalid_argument` for unrecognised negative numbers.

    val signal_of_int : int -> signal

`signal_of_int n` converts a platform-dependent signal number `n` to an OCaml signal number.

For positive `n` this is `n` itself if OCaml does not have a platform-independent signal number for `n`.

- Since 5.4
- Raises `Invalid_argument` if `n` is negative.

    val signal_to_int : signal -> int

`signal_to_int n` converts an OCaml signal number `n` to a platform-dependent signal number.

For positive `n` this is `n` itself.

- Since 5.4
- Raises `Invalid_argument` for unrecognised negative numbers.

    exception Break

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

    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.

Inside multi-threaded programs, the `Break` exception will arise in any one of the active threads, and will keep arising on further interactive interrupt until all threads are terminated. Use signal masks from `Thread.sigmask` to direct the interrupt towards a specific thread.

    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]` part was absent before version 3.08.0 and became mandatory from 3.08.0 onwards. The `[(+|~)additional-info]` part may be absent.

    val development_version : bool

`true` if this is a development version, `false` otherwise.

- Since 4.14

    type extra_prefix =

`|` | `Plus`
`|` | `Tilde`

    type extra_info = extra_prefix * string

- Since 4.14

    type ocaml_release_info = {

`` | `major : `int`;`
`` | `minor : `int`;`
`` | `patchlevel : `int`;`
`` | `extra : `extra_info option`;`

`}`

- Since 4.14

    val ocaml_release : ocaml_release_info

`ocaml_release` is the version of OCaml.

- Since 4.14

    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 disabled by default.

- Since 4.03
- Alert unsynchronized_access. The status of runtime warnings is a mutable global state.

    val runtime_warnings_enabled : unit -> bool

Return whether runtime warnings are currently enabled.

- Since 4.03
- Alert unsynchronized_access. The status of runtime warnings is a mutable global state.

## 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. However, it does prevent the argument from being garbage collected until the location where the call would have occurred.

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

    module Immediate64: sig .. end