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os(3erl) | Erlang Module Definition | 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 platformNotice 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 9:55:30.051711OS 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.
kernel 5.1.1 | Ericsson AB |