os
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.
Functions
cmd(Command) -> string()
Command = atom() | io_lib:chars()
Executes
in a command shell of the
target OS,
captures the standard output of the command, and returns this
result as a string. This function is a replacement of
the previous function unix:cmd/1
; they are equivalent on a
Unix platform.
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.
find_executable(Name) -> Filename | false
Name = Filename = string()
find_executable(Name, Path) -> Filename | false
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 underlying
OS. find_executable/1
uses the current
execution path (that is, the environment variable PATH
on
Unix and Windows).
, if specified, is to conform to the syntax
of execution paths on the OS. Returns the absolute filename of the
executable program
,
or false
if the program is not found.
getenv() -> [string()]
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.
getenv(VarName) -> Value | false
VarName = Value = string()
Returns the
of the environment variable
, or false
if the environment
variable is undefined.
If Unicode filename encoding is in effect (see the
erl
manual
page), the strings
and
can contain characters with
codepoints > 255.
getenv(VarName, DefaultValue) -> Value
VarName = DefaultValue = Value = string()
Returns the
of the environment variable
, or DefaultValue
if the
environment variable is undefined.
If Unicode filename encoding is in effect (see the
erl
manual
page), the strings
and
can contain characters with
codepoints > 255.
getpid() -> Value
Value = string()
Returns the process identifier of the current Erlang emulator
in the format most commonly used by the OS environment.
Returns
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
VarName = Value = string()
Sets a new
for environment variable
.
If Unicode filename encoding is in effect (see the
erl
manual
page), the strings
and
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.
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()
Unit = erlang:time_unit()
Returns the current
OS system time
converted into the
passed as argument.
Calling os:system_time(
is equivalent to
erlang:convert_time_unit
(os:system_time()
,
native,
.
Note!
This time is not a monotonically increasing time.
timestamp() -> Timestamp
Timestamp = erlang:timestamp()
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 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 retreived by
system_time/0
and
system_time/1
.
perf_counter() -> Counter
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()
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}
Osfamily = unix | win32
Osname = atom()
Returns the
and, in some cases, the
of the current OS.
On Unix,
has the same value as
uname -s
returns, but in lower case. For example, on
Solaris 1 and 2, it is sunos
.
On Windows,
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
.
unsetenv(VarName) -> true
VarName = string()
Deletes the environment variable
.
If Unicode filename encoding is in effect (see the
erl
manual
page), the string
can
contain characters with codepoints > 255.
version() -> VersionString | {Major, Minor, Release}
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 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.