module Sys: Sysval argv : string arrayThe 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 : stringThe 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 -> boolTest if a file with the given name exists.
val is_directory : string -> boolReturns true if the given name refers to a directory,
    false if it refers to another kind of file.
Sys_error if no file exists with the given name.val is_regular_file : string -> boolReturns true if the given name refers to a regular file,
    false if it refers to another kind of file.
Sys_error if no file exists with the given name.val remove : string -> unitRemove the given file name from the file system.
val rename : string -> string -> unitRename 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.
val getenv : string -> stringReturn the value associated to a variable in the process environment.
Not_found if the variable is unbound.val getenv_opt : string -> string optionReturn the value associated to a variable in the process
    environment or None if the variable is unbound.
val command : string -> intExecute 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 -> floatReturn the processor time, in seconds, used by the program since the beginning of execution.
val chdir : string -> unitChange the current working directory of the process.
val mkdir : string -> int -> unitCreate a directory with the given permissions.
val rmdir : string -> unitRemove an empty directory.
val getcwd : unit -> stringReturn the current working directory of the process.
val readdir : string -> string arrayReturn 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 : intSize 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.
val interactive : bool refThis 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 : stringOperating 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 | | | Native | 
| | | Bytecode | 
| | | Other of  | 
Currently, the official distribution only supports Native and
    Bytecode, but it can be other backends with alternative
    compilers, for example, javascript.
val backend_type : backend_typeBackend type currently executing the OCaml program.
val unix : boolTrue if Sys.os_type = "Unix".
val win32 : boolTrue if Sys.os_type = "Win32".
val cygwin : boolTrue if Sys.os_type = "Cygwin".
val word_size : intSize of one word on the machine currently executing the OCaml program, in bits: 32 or 64.
val int_size : intSize 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.
val big_endian : boolWhether the machine currently executing the Caml program is big-endian.
val max_string_length : intMaximum length of strings and byte sequences.
val max_array_length : intMaximum 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 : intMaximum 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 -> stringReturn 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.
val runtime_parameters : unit -> stringReturn the value of the runtime parameters, in the same format
    as the contents of the OCAMLRUNPARAM environment variable.
val poll_actions : unit -> unitRun any pending runtime actions, such as minor collections, major GC slices, signal handlers, finalizers, or memprof callbacks.
typesignal =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.
type | | | Signal_default | 
| | | Signal_ignore | 
| | | Signal_handle of  | 
What to do when receiving a signal:
Signal_default: take the default behavior
     (usually: abort the program)Signal_ignore: ignore the signalSignal_handle f: call function f, giving it the signal
   number as an argument.val signal : signal -> signal_behavior -> signal_behaviorSet 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 -> unitSame as Sys.signal but the return value is ignored.
val sigabrt : signalAbnormal termination
val sigalrm : signalTimeout
val sigfpe : signalArithmetic exception
val sighup : signalHangup on controlling terminal
val sigill : signalInvalid hardware instruction
val sigint : signalInteractive interrupt (ctrl-C)
val sigkill : signalTermination (cannot be ignored)
val sigpipe : signalBroken pipe
val sigquit : signalInteractive termination
val sigsegv : signalInvalid memory reference
val sigterm : signalTermination
val sigusr1 : signalApplication-defined signal 1
val sigusr2 : signalApplication-defined signal 2
val sigchld : signalChild process terminated
val sigcont : signalContinue
val sigstop : signalStop (cannot be caught or ignored)
val sigtstp : signalInteractive stop
val sigttin : signalTerminal read from background process
val sigttou : signalTerminal write from background process
val sigvtalrm : signalTimeout in virtual time
val sigprof : signalProfiling interrupt
val sigbus : signalBus error
val sigpoll : signalPollable event
val sigsys : signalBad argument to routine
val sigtrap : signalTrace/breakpoint trap
val sigurg : signalUrgent condition on socket
val sigxcpu : signalTimeout in cpu time
val sigxfsz : signalFile size limit exceeded
val sigio : signalI/O is possible on a descriptor
val sigwinch : signalWindow size change
val signal_to_string : signal -> stringsignal_to_string formats an OCaml signal as a C POSIX
    
    constant or "SIG(%d)" for platform-dependent signal numbers.
Invalid_argument for unrecognised negative numbers.val signal_of_int : int -> signalsignal_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.
Invalid_argument if n is negative.val signal_to_int : signal -> intsignal_to_int n converts an OCaml signal number n to
    a platform-dependent signal number.
For positive n this is n itself.
Invalid_argument for unrecognised negative numbers.exception Break
Exception raised on interactive interrupt if Sys.catch_break
   is enabled.
val catch_break : bool -> unitcatch_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 : stringocaml_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 : booltrue if this is a development version, false otherwise.
type | | | Plus | 
| | | Tilde | 
typeextra_info =extra_prefix * string
type |    | major :  | 
|    | minor :  | 
|    | patchlevel :  | 
|    | extra :  | 
}
val ocaml_release : ocaml_release_infoocaml_release is the version of OCaml.
val enable_runtime_warnings : bool -> unitControl 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.
val runtime_warnings_enabled : unit -> boolReturn whether runtime warnings are currently enabled.
val opaque_identity : 'a -> 'aFor 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
    module Immediate64:sig..end