View Source os (kernel v9.3)

Operating system-specific functions.

The functions in this module are operating system-specific. Careless use of these functions results in programs that will only run on a specific platform. On the other hand, with careful use, these functions can be of help in enabling a program to run on most platforms.

Note

The functions in this module will raise a badarg exception if their arguments contain invalid characters according to the description in the "Data Types" section.

Summary

Types

A string containing valid characters on the specific OS for environment variable names using file:native_name_encoding() encoding.

Assuming that environment variables has been correctly set, a strings containing valid characters on the specific OS for environment variable names and values using file:native_name_encoding() encoding.

A string containing valid characters on the specific OS for environment variable values using file:native_name_encoding() encoding.

All characters needs to be valid characters on the specific OS using file:native_name_encoding() encoding. Null characters (integer value zero) are not allowed.

Functions

Executes Command in a command shell of the target OS, captures the standard output and standard error of the command, and returns this result as a string.

The possible options are

Returns a list of all environment variables. Each environment variable is expressed as a tuple {VarName,Value}, where VarName is the name of the variable and Value its value.

Equivalent to find_executable(Name, Path) where Path is the current execution path (that is, the environment variable PATH on Unix and Windows).

Look up an executable program, with the specified name and a search path, in the same way as the underlying OS.

Returns a list of all environment variables. Each environment variable is expressed as a single string on the format "VarName=Value", where VarName is the name of the variable and Value its value.

Returns the Value of the environment variable VarName, or false if the environment variable is undefined.

Returns the Value of the environment variable VarName, or DefaultValue if the environment variable is undefined.

Returns the process identifier of the current Erlang emulator in the format most commonly used by the OS environment.

Returns the current performance counter value in perf_counter time unit. This is a highly optimized call that might not be traceable.

Returns a performance counter that can be used as a very fast and high resolution timestamp.

Sets a new Value for environment variable VarName.

Enables or disables OS signals.

Returns the current OS system time in native time unit.

Returns the current OS system time converted into the Unit passed as argument.

Returns the current OS system time in the same format as erlang:timestamp/0.

Returns the Osfamily and, in some cases, the Osname of the current OS.

Deletes the environment variable VarName.

Returns the OS version. On most systems, this function returns a tuple, but a string is returned instead if the system has versions that cannot be expressed as three numbers.

Types

-type env_var_name() :: nonempty_string().

A string containing valid characters on the specific OS for environment variable names using file:native_name_encoding() encoding.

Null characters (integer value zero) are not allowed. On Unix, = characters are not allowed. On Windows, a = character is only allowed as the very first character in the string.

-type env_var_name_value() :: nonempty_string().

Assuming that environment variables has been correctly set, a strings containing valid characters on the specific OS for environment variable names and values using file:native_name_encoding() encoding.

The first = characters appearing in the string separates environment variable name (on the left) from environment variable value (on the right).

-type env_var_value() :: string().

A string containing valid characters on the specific OS for environment variable values using file:native_name_encoding() encoding.

Null characters (integer value zero) are not allowed.

-type os_command() :: atom() | io_lib:chars().

All characters needs to be valid characters on the specific OS using file:native_name_encoding() encoding. Null characters (integer value zero) are not allowed.

-type os_command_opts() :: #{max_size => non_neg_integer() | infinity}.

Options for os:cmd/2.

  • max_size - The maximum size of the data returned by the os:cmd/2 call. See the os:cmd/2 documentation for more details.

Functions

-spec cmd(Command) -> string() when Command :: os_command().

Executes Command in a command shell of the target OS, captures the standard output and standard error of the command, and returns this result as a string.

Examples:

LsOut = os:cmd("ls"), % on unix platform
DirOut = os:cmd("dir"), % on Win32 platform

Notice that in some cases, standard output of a command when called from another program can differ, compared with the standard output of the command when called directly from an OS command shell.

Link to this function

cmd(Command, Options)

View Source (since OTP 20.2.3)
-spec cmd(Command, Options) -> string() when Command :: os_command(), Options :: os_command_opts().

The possible options are:

  • max_size - The maximum size of the data returned by the os:cmd call. This option is a safety feature that should be used when the command executed can return a very large, possibly infinite, result.

    > os:cmd("cat /dev/zero", #{ max_size => 20 }).
    [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
-spec env() -> [{env_var_name(), env_var_value()}].

Returns a list of all environment variables. Each environment variable is expressed as a tuple {VarName,Value}, where VarName is the name of the variable and Value its value.

If Unicode filename encoding is in effect (see the erl manual page), the strings can contain characters with codepoints > 255.

-spec find_executable(Name) -> Filename | false when Name :: string(), Filename :: string().

Equivalent to find_executable(Name, Path) where Path is the current execution path (that is, the environment variable PATH on Unix and Windows).

Link to this function

find_executable(Name, Path)

View Source
-spec find_executable(Name, Path) -> Filename | false
                   when Name :: string(), Path :: string(), Filename :: string().

Look up an executable program, with the specified name and a search path, in the same way as the underlying OS.

Path is to conform to the syntax of execution paths on the OS. Returns the absolute filename of the executable program Name, or false if the program is not found.

-spec getenv() -> [env_var_name_value()].

Returns a list of all environment variables. Each environment variable is expressed as a single string on the format "VarName=Value", where VarName is the name of the variable and Value its value.

If Unicode filename encoding is in effect (see the erl manual page), the strings can contain characters with codepoints > 255.

Consider using env/0 for a nicer 2-tuple format.

-spec getenv(VarName) -> Value | false when VarName :: env_var_name(), Value :: env_var_value().

Returns the Value of the environment variable VarName, or false if the environment variable is undefined.

If Unicode filename encoding is in effect (see the erl manual page), the strings VarName and Value can contain characters with codepoints > 255.

Link to this function

getenv(VarName, DefaultValue)

View Source (since OTP 18.0)
-spec getenv(VarName, DefaultValue) -> Value
          when
              VarName :: env_var_name(), DefaultValue :: env_var_value(), Value :: env_var_value().

Returns the Value of the environment variable VarName, or DefaultValue if the environment variable is undefined.

If Unicode filename encoding is in effect (see the erl manual page), the strings VarName and Value can contain characters with codepoints > 255.

-spec getpid() -> Value when Value :: string().

Returns the process identifier of the current Erlang emulator in the format most commonly used by the OS environment.

Returns Value as a string containing the (usually) numerical identifier for a process.

  • On Unix, this is typically the return value of the getpid/0 system call.
  • On Windows, the process id as returned by the GetCurrentProcessId() system call is used.
Link to this function

perf_counter()

View Source (since OTP 19.0)
-spec perf_counter() -> Counter when Counter :: integer().

Returns the current performance counter value in perf_counter time unit. This is a highly optimized call that might not be traceable.

Link to this function

perf_counter(Unit)

View Source (since OTP 19.0)
-spec perf_counter(Unit) -> integer() when Unit :: erlang:time_unit().

Returns a performance counter that can be used as a very fast and high resolution timestamp.

This counter is read directly from the hardware or operating system with the same guarantees. This means that two consecutive calls to the function are not guaranteed to be monotonic, though it most likely will be. The performance counter will be converted to the resolution passed as an argument.

1> T1 = os:perf_counter(1000),receive after 10000 -> ok end,T2 = os:perf_counter(1000).
176525861
2> T2 - T1.
10004
-spec putenv(VarName, Value) -> true when VarName :: env_var_name(), Value :: env_var_value().

Sets a new Value for environment variable VarName.

If Unicode filename encoding is in effect (see the erl manual page), the strings VarName and Value can contain characters with codepoints > 255.

On Unix platforms, the environment is set using UTF-8 encoding if Unicode filename translation is in effect. On Windows, the environment is set using wide character interfaces.

Link to this function

set_signal(Signal, Option)

View Source (since OTP 20.0)
-spec set_signal(Signal, Option) -> ok
              when
                  Signal ::
                      sighup | sigquit | sigabrt | sigalrm | sigterm | sigusr1 | sigusr2 |
                      sigchld | sigstop | sigtstp,
                  Option :: default | handle | ignore.

Enables or disables OS signals.

Each signal my be set to one of the following options:

  • ignore - This signal will be ignored.

  • default - This signal will use the default signal handler for the operating system.

  • handle - This signal will notify erl_signal_server when it is received by the Erlang runtime system.

Link to this function

system_time()

View Source (since OTP 18.0)
-spec system_time() -> integer().

Returns the current OS system time in native time unit.

Note

This time is not a monotonically increasing time.

Link to this function

system_time(Unit)

View Source (since OTP 18.0)
-spec system_time(Unit) -> integer() when Unit :: erlang:time_unit().

Returns the current OS system time converted into the Unit passed as argument.

Calling os:system_time(Unit) is equivalent to erlang:convert_time_unit(os:system_time(), native, Unit).

Note

This time is not a monotonically increasing time.

-spec timestamp() -> Timestamp when Timestamp :: erlang:timestamp().

Returns the current OS system time in the same format as erlang:timestamp/0.

The tuple can be used together with function calendar:now_to_universal_time/1 or calendar:now_to_local_time/1 to get calendar time. Using the calendar time, together with the MicroSecs part of the return tuple from this function, allows you to log time stamps in high resolution and consistent with the time in the rest of the OS.

Example of code formatting a string in format "DD Mon YYYY HH:MM:SS.mmmmmm", where DD is the day of month, Mon is the textual month name, YYYY is the year, HH:MM:SS is the time, and mmmmmm is the microseconds in six positions:

-module(print_time).
-export([format_utc_timestamp/0]).
format_utc_timestamp() ->
    TS = {_,_,Micro} = os:timestamp(),
    {{Year,Month,Day},{Hour,Minute,Second}} =
calendar:now_to_universal_time(TS),
    Mstr = element(Month,{"Jan","Feb","Mar","Apr","May","Jun","Jul",
    "Aug","Sep","Oct","Nov","Dec"}),
    io_lib:format("~2w ~s ~4w ~2w:~2..0w:~2..0w.~6..0w",
    [Day,Mstr,Year,Hour,Minute,Second,Micro]).

This module can be used as follows:

1> io:format("~s~n",[print_time:format_utc_timestamp()]).
29 Apr 2009  9:55:30.051711

OS system time can also be retrieved by system_time/0 and system_time/1.

-spec type() -> {Osfamily, Osname} when Osfamily :: unix | win32, Osname :: atom().

Returns the Osfamily and, in some cases, the Osname of the current OS.

On Unix, Osname has the same value as uname -s returns, but in lower case. For example, on Solaris 1 and 2, it is sunos.

On Windows, Osname is nt.

Note

Think twice before using this function. Use module filename if you want to inspect or build filenames in a portable way. Avoid matching on atom Osname.

Link to this function

unsetenv(VarName)

View Source (since OTP R16B03)
-spec unsetenv(VarName) -> true when VarName :: env_var_name().

Deletes the environment variable VarName.

If Unicode filename encoding is in effect (see the erl manual page), the string VarName can contain characters with codepoints > 255.

-spec version() -> VersionString | {Major, Minor, Release}
           when
               VersionString :: string(),
               Major :: non_neg_integer(),
               Minor :: non_neg_integer(),
               Release :: non_neg_integer().

Returns the OS version. On most systems, this function returns a tuple, but a string is returned instead if the system has versions that cannot be expressed as three numbers.

Note

Think twice before using this function. If you still need to use it, always call os:type() first.