os(3erl)
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 specific platform. On the other hand, with careful use, these functions can be of help in enabling a program to run on most platforms.
EXPORTS
cmd(Command) -> string()
Types:
Command = atom() | io_lib:chars()
Executes Command 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
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
underlying 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() -> [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
Types:
VarName = Value = string()
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 = DefaultValue = Value = string()
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 = Value = string()
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.
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:convert_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
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
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
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.
unsetenv(VarName) -> true
Types:
VarName = string()
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
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.
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