.TH "Sys" 3o source: 2019-01-25 OCamldoc "OCaml library"
.SH NAME
Sys \- System interface.
.SH Module
Module   Sys
.SH Documentation
.sp
Module
.BI "Sys"
 : 
.B sig  end

.sp
System interface\&.
.sp
Every function in this module raises 
.B Sys_error
with an
informative message when the underlying system call signal
an error\&.

.sp

.sp
.sp

.I val argv 
: 
.B string array
.sp
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\&.

.sp

.I val executable_name 
: 
.B string
.sp
The name of the file containing the executable currently running\&.

.sp

.I val file_exists 
: 
.B string -> bool
.sp
Test if a file with the given name exists\&.

.sp

.I val is_directory 
: 
.B string -> bool
.sp
Returns 
.B true
if the given name refers to a directory,
.B false
if it refers to another kind of file\&.
Raise 
.B Sys_error
if no file exists with the given name\&.

.sp
.B "Since"
3.10.0

.sp

.I val remove 
: 
.B string -> unit
.sp
Remove the given file name from the file system\&.

.sp

.I val rename 
: 
.B string -> string -> unit
.sp
Rename a file\&. The first argument is the old name and the
second is the new name\&. If there is already another file
under the new name, 
.B rename
may replace it, or raise an
exception, depending on your operating system\&.

.sp

.I val getenv 
: 
.B string -> string
.sp
Return the value associated to a variable in the process
environment\&. Raise 
.B Not_found
if the variable is unbound\&.

.sp

.I val getenv_opt 
: 
.B string -> string option
.sp
Return the value associated to a variable in the process
environment or 
.B None
if the variable is unbound\&.

.sp
.B "Since"
4.05

.sp

.I val command 
: 
.B string -> int
.sp
Execute the given shell command and return its exit code\&.

.sp

.I val time 
: 
.B unit -> float
.sp
Return the processor time, in seconds, used by the program
since the beginning of execution\&.

.sp

.I val chdir 
: 
.B string -> unit
.sp
Change the current working directory of the process\&.

.sp

.I val getcwd 
: 
.B unit -> string
.sp
Return the current working directory of the process\&.

.sp

.I val readdir 
: 
.B string -> string array
.sp
Return the names of all files present in the given directory\&.
Names denoting the current directory and the parent directory
(
.B "\&."
and 
.B "\&.\&."
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\&.

.sp

.I val interactive 
: 
.B bool Pervasives.ref
.sp
This reference is initially set to 
.B false
in standalone
programs and to 
.B true
if the code is being executed under
the interactive toplevel system 
.B ocaml
\&.

.sp

.I val os_type 
: 
.B string
.sp
Operating system currently executing the OCaml program\&. One of
.sp
\- 
.B "Unix"
(for all Unix versions, including Linux and Mac OS X),
.sp
\- 
.B "Win32"
(for MS\-Windows, OCaml compiled with MSVC++ or Mingw),
.sp
\- 
.B "Cygwin"
(for MS\-Windows, OCaml compiled with Cygwin)\&.


.sp
.I type backend_type 
=
 | Native
 | Bytecode
 | Other
.B of 
.B string
 
.sp
Currently, the official distribution only supports 
.B Native
and
.B Bytecode
, but it can be other backends with alternative
compilers, for example, javascript\&.

.sp
.B "Since"
4.04.0

.sp

.I val backend_type 
: 
.B backend_type
.sp
Backend type  currently executing the OCaml program\&.

.sp
.B "Since"
4.04.0

.sp

.I val unix 
: 
.B bool
.sp
True if 
.B Sys\&.os_type = "Unix"
\&.

.sp
.B "Since"
4.01.0

.sp

.I val win32 
: 
.B bool
.sp
True if 
.B Sys\&.os_type = "Win32"
\&.

.sp
.B "Since"
4.01.0

.sp

.I val cygwin 
: 
.B bool
.sp
True if 
.B Sys\&.os_type = "Cygwin"
\&.

.sp
.B "Since"
4.01.0

.sp

.I val word_size 
: 
.B int
.sp
Size of one word on the machine currently executing the OCaml
program, in bits: 32 or 64\&.

.sp

.I val int_size 
: 
.B int
.sp
Size of an int\&.  It is 31 bits (resp\&. 63 bits) when using the
OCaml compiler on a 32 bits (resp\&. 64 bits) platform\&.  It may
differ for other compilers, e\&.g\&. it is 32 bits when compiling to
JavaScript\&.

.sp
.B "Since"
4.03.0

.sp

.I val big_endian 
: 
.B bool
.sp
Whether the machine currently executing the Caml program is big\-endian\&.

.sp
.B "Since"
4.00.0

.sp

.I val max_string_length 
: 
.B int
.sp
Maximum length of strings and byte sequences\&.

.sp

.I val max_array_length 
: 
.B int
.sp
Maximum length of a normal array\&.  The maximum length of a float
array is 
.B max_array_length/2
on 32\-bit machines and
.B max_array_length
on 64\-bit machines\&.

.sp

.I val runtime_variant 
: 
.B unit -> string
.sp
Return the name of the runtime variant the program is running on\&.
This is normally the argument given to 
.B \-runtime\-variant
at compile
time, but for byte\-code it can be changed after compilation\&.

.sp
.B "Since"
4.03.0

.sp

.I val runtime_parameters 
: 
.B unit -> string
.sp
Return the value of the runtime parameters, in the same format
as the contents of the 
.B OCAMLRUNPARAM
environment variable\&.

.sp
.B "Since"
4.03.0

.sp

.PP

.B === 
.B Signal handling
.B  ===

.PP
.I type signal_behavior 
=
 | Signal_default
 | Signal_ignore
 | Signal_handle
.B of 
.B (int -> unit)
 
.sp
What to do when receiving a signal:
.sp
\-
.B Signal_default
: take the default behavior
(usually: abort the program)
.sp
\-
.B Signal_ignore
: ignore the signal
.sp
\-
.B Signal_handle f
: call function 
.B f
, giving it the signal
number as argument\&.


.sp

.I val signal 
: 
.B int -> signal_behavior -> signal_behavior
.sp
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 
.B Invalid_argument
exception is raised\&.

.sp

.I val set_signal 
: 
.B int -> signal_behavior -> unit
.sp
Same as 
.B Sys\&.signal
but return value is ignored\&.

.sp

.PP

.B === 
.B Signal numbers for the standard POSIX signals\&.
.B  ===

.PP

.I val sigabrt 
: 
.B int
.sp
Abnormal termination

.sp

.I val sigalrm 
: 
.B int
.sp
Timeout

.sp

.I val sigfpe 
: 
.B int
.sp
Arithmetic exception

.sp

.I val sighup 
: 
.B int
.sp
Hangup on controlling terminal

.sp

.I val sigill 
: 
.B int
.sp
Invalid hardware instruction

.sp

.I val sigint 
: 
.B int
.sp
Interactive interrupt (ctrl\-C)

.sp

.I val sigkill 
: 
.B int
.sp
Termination (cannot be ignored)

.sp

.I val sigpipe 
: 
.B int
.sp
Broken pipe

.sp

.I val sigquit 
: 
.B int
.sp
Interactive termination

.sp

.I val sigsegv 
: 
.B int
.sp
Invalid memory reference

.sp

.I val sigterm 
: 
.B int
.sp
Termination

.sp

.I val sigusr1 
: 
.B int
.sp
Application\-defined signal 1

.sp

.I val sigusr2 
: 
.B int
.sp
Application\-defined signal 2

.sp

.I val sigchld 
: 
.B int
.sp
Child process terminated

.sp

.I val sigcont 
: 
.B int
.sp
Continue

.sp

.I val sigstop 
: 
.B int
.sp
Stop

.sp

.I val sigtstp 
: 
.B int
.sp
Interactive stop

.sp

.I val sigttin 
: 
.B int
.sp
Terminal read from background process

.sp

.I val sigttou 
: 
.B int
.sp
Terminal write from background process

.sp

.I val sigvtalrm 
: 
.B int
.sp
Timeout in virtual time

.sp

.I val sigprof 
: 
.B int
.sp
Profiling interrupt

.sp

.I val sigbus 
: 
.B int
.sp
Bus error

.sp
.B "Since"
4.03

.sp

.I val sigpoll 
: 
.B int
.sp
Pollable event

.sp
.B "Since"
4.03

.sp

.I val sigsys 
: 
.B int
.sp
Bad argument to routine

.sp
.B "Since"
4.03

.sp

.I val sigtrap 
: 
.B int
.sp
Trace/breakpoint trap

.sp
.B "Since"
4.03

.sp

.I val sigurg 
: 
.B int
.sp
Urgent condition on socket

.sp
.B "Since"
4.03

.sp

.I val sigxcpu 
: 
.B int
.sp
Timeout in cpu time

.sp
.B "Since"
4.03

.sp

.I val sigxfsz 
: 
.B int
.sp
File size limit exceeded

.sp
.B "Since"
4.03

.sp

.I exception Break 

.sp
Exception raised on interactive interrupt if 
.B Sys\&.catch_break
is on\&.

.sp

.I val catch_break 
: 
.B bool -> unit
.sp

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

.sp

.I val ocaml_version 
: 
.B string
.sp

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

.sp

.I val enable_runtime_warnings 
: 
.B bool -> unit
.sp
Control whether the OCaml runtime system can emit warnings
on stderr\&.  Currently, the only supported warning is triggered
when a channel created by 
.B open_*
functions is finalized without
being closed\&.  Runtime warnings are enabled by default\&.

.sp
.B "Since"
4.03.0

.sp

.I val runtime_warnings_enabled 
: 
.B unit -> bool
.sp
Return whether runtime warnings are currently enabled\&.

.sp
.B "Since"
4.03.0

.sp

.PP

.B === 
.B Optimization
.B  ===

.PP

.I val opaque_identity 
: 
.B 'a -> 'a
.sp
For the purposes of optimization, 
.B opaque_identity
behaves like an
unknown (and thus possibly side\-effecting) function\&.
.sp
At runtime, 
.B opaque_identity
disappears altogether\&.
.sp
A typical use of this function is to prevent pure computations from being
optimized away in benchmarking loops\&.  For example:
.B 
.B       for _round = 1 to 100_000 do
.B         ignore (Sys\&.opaque_identity (my_pure_computation ()))
.B       done
.B     


.sp
.B "Since"
4.03.0

.sp