os - specific functions.
Please see following description for synopsis
os(3) Erlang Module Definition os(3)
NAME
os - Operating system-specific functions.
DESCRIPTION
The functions in this module are operating system-specific. Careless
use of these functions results in programs that will only run on a spe-
cific 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.
DATA TYPES
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.
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.
env_var_name_value() = nonempty_string()
Assuming that environment variables has been correctly set, a
strings containing valid characters on the specific OS for envi-
ronment variable names and values using file:native_name_encod-
ing() encoding. The first = characters appearing in the string
separates environment variable name (on the left) from environ-
ment variable value (on the right).
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.
os_command_opts() = #{max_size => integer() >= 0 | 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.
EXPORTS
cmd(Command) -> string()
cmd(Command, Options) -> string()
Types:
Command = os_command()
Options = os_command_opts()
Executes Command in a command shell of the target OS, captures
the standard output 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 (for example, os:cmd/1) can differ,
compared with the standard output of the command when called
directly from an OS command shell.
os:cmd/2 was added in kernel-5.5 (OTP-20.2.1). It makes it pos-
sible to pass an options map as the second argument in order to
control the behaviour of os:cmd. 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]
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.
find_executable(Name) -> Filename | false
find_executable(Name, Path) -> Filename | false
Types:
Name = Path = Filename = string()
These two functions look up an executable program, with the
specified name and a search path, in the same way as the under-
lying OS. find_executable/1 uses the current execution path
(that is, the environment variable PATH on Unix and Windows).
Path, if specified, 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.
getenv() -> [env_var_name_value()]
Returns a list of all environment variables. Each environment
variable is expressed as a single string on the format "Var-
Name=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.
getenv(VarName) -> Value | false
Types:
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.
getenv(VarName, DefaultValue) -> Value
Types:
VarName = env_var_name()
DefaultValue = 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.
getpid() -> Value
Types:
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() system call. On Windows, the process id as returned
by the GetCurrentProcessId() system call is used.
putenv(VarName, Value) -> true
Types:
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.
set_signal(Signal, Option) -> ok
Types:
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.
system_time() -> integer()
Returns the current OS system time in native time unit.
Note:
This time is not a monotonically increasing time.
system_time(Unit) -> integer()
Types:
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:con-
vert_time_unit(os:system_time(), native, Unit).
Note:
This time is not a monotonically increasing time.
timestamp() -> Timestamp
Types:
Timestamp = erlang:timestamp()
Timestamp = {MegaSecs, Secs, MicroSecs}
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 tex-
tual 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 retreived by system_time/0 and sys-
tem_time/1.
perf_counter() -> Counter
Types:
Counter = integer()
Returns the current performance counter value in perf_counter
time unit. This is a highly optimized call that might not be
traceable.
perf_counter(Unit) -> integer()
Types:
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
type() -> {Osfamily, Osname}
Types:
Osfamily = unix | win32
Osname = atom()
Returns the Osfamily and, in some cases, the Osname of the cur-
rent 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.
unsetenv(VarName) -> true
Types:
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.
version() -> VersionString | {Major, Minor, Release}
Types:
VersionString = string()
Major = Minor = Release = integer() >= 0
Returns the OS version. On most systems, this function returns a
tuple, but a string is returned instead if the system has ver-
sions 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.
Ericsson AB kernel 8.2 os(3)