Module Sys
: sigend
System interface.
Every function in this module raises Sys_error with an informative message when the underlying system
call signal an error.
valargv : stringarray
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.
valexecutable_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.
valfile_exists : string->bool
Test if a file with the given name exists.
valis_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
RaisesSys_error if no file exists with the given name.
valis_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
RaisesSys_error if no file exists with the given name.
valremove : string->unit
Remove the given file name from the file system.
valrename : string->string->unit
Rename a file or directory. renameoldpathnewpath 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
valgetenv : string->string
Return the value associated to a variable in the process environment.
RaisesNot_found if the variable is unbound.
valgetenv_opt : string->stringoption
Return the value associated to a variable in the process environment or None if the variable is unbound.
Since 4.05
valcommand : 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.
valtime : unit->float
Return the processor time, in seconds, used by the program since the beginning of execution.
valchdir : string->unit
Change the current working directory of the process.
valmkdir : string->int->unit
Create a directory with the given permissions.
Since 4.12
valrmdir : string->unit
Remove an empty directory.
Since 4.12
valgetcwd : unit->string
Return the current working directory of the process.
valreaddir : string->stringarray
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.
valinteractive : boolref
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 .
Alertunsynchronized_access. The interactive status is a mutable global state.
valos_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).
typebackend_type =
| Native
| Bytecode
| Other ofstring
Currently, the official distribution only supports Native and Bytecode , but it can be other backends
with alternative compilers, for example, javascript.
Since 4.04
valbackend_type : backend_type
Backend type currently executing the OCaml program.
Since 4.04
valunix : bool
True if Sys.os_type="Unix" .
Since 4.01
valwin32 : bool
True if Sys.os_type="Win32" .
Since 4.01
valcygwin : bool
True if Sys.os_type="Cygwin" .
Since 4.01
valword_size : int
Size of one word on the machine currently executing the OCaml program, in bits: 32 or 64.
valint_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
valbig_endian : bool
Whether the machine currently executing the Caml program is big-endian.
Since 4.00
valmax_string_length : int
Maximum length of strings and byte sequences.
valmax_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 floatarray is max_floatarray_length if OCaml was configured with --enable-flat-float-array
and max_array_length if configured with --disable-flat-float-array .
valmax_floatarray_length : int
Maximum length of a floatarray. This is also the maximum length of a floatarray when OCaml is configured
with --enable-flat-float-array .
valruntime_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
valruntime_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
valpoll_actions : unit->unit
Run any pending runtime actions, such as minor collections, major GC slices, signal handlers, finalizers,
or memprof callbacks.
Since 5.3
Signalhandlingtypesignal_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_handlef : call function f , giving it the signal number as argument.
valsignal : 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.
valset_signal : int->signal_behavior->unit
Same as Sys.signal but return value is ignored.
SignalnumbersforthestandardPOSIXsignals.valsigabrt : int
Abnormal termination
valsigalrm : int
Timeout
valsigfpe : int
Arithmetic exception
valsighup : int
Hangup on controlling terminal
valsigill : int
Invalid hardware instruction
valsigint : int
Interactive interrupt (ctrl-C)
valsigkill : int
Termination (cannot be ignored)
valsigpipe : int
Broken pipe
valsigquit : int
Interactive termination
valsigsegv : int
Invalid memory reference
valsigterm : int
Termination
valsigusr1 : int
Application-defined signal 1
valsigusr2 : int
Application-defined signal 2
valsigchld : int
Child process terminated
valsigcont : int
Continue
valsigstop : int
Stop
valsigtstp : int
Interactive stop
valsigttin : int
Terminal read from background process
valsigttou : int
Terminal write from background process
valsigvtalrm : int
Timeout in virtual time
valsigprof : int
Profiling interrupt
valsigbus : int
Bus error
Since 4.03
valsigpoll : int
Pollable event
Since 4.03
valsigsys : int
Bad argument to routine
Since 4.03
valsigtrap : int
Trace/breakpoint trap
Since 4.03
valsigurg : int
Urgent condition on socket
Since 4.03
valsigxcpu : int
Timeout in cpu time
Since 4.03
valsigxfsz : int
File size limit exceeded
Since 4.03
exceptionBreak
Exception raised on interactive interrupt if Sys.catch_break is enabled.
valcatch_break : bool->unitcatch_break governs whether interactive interrupt (ctrl-C) terminates the program or raises the Break
exception. Call catch_breaktrue to enable raising Break , and catch_breakfalse 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.
valocaml_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.
valdevelopment_version : booltrue if this is a development version, false otherwise.
Since 4.14
typeextra_prefix =
| Plus
| Tilde
typeextra_info = extra_prefix*stringSince 4.14
typeocaml_release_info = {
major : int ;
minor : int ;
patchlevel : int ;
extra : extra_infooption ;
}
Since 4.14
valocaml_release : ocaml_release_infoocaml_release is the version of OCaml.
Since 4.14
valenable_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
Alertunsynchronized_access. The status of runtime warnings is a mutable global state.
valruntime_warnings_enabled : unit->bool
Return whether runtime warnings are currently enabled.
Since 4.03
Alertunsynchronized_access. The status of runtime warnings is a mutable global state.
Optimizationvalopaque_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=1to100_000doignore(Sys.opaque_identity(my_pure_computation()))doneSince 4.03
moduleImmediate64:sigend
OCamldoc 2025-06-12 Sys(3o)
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