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os(3erl) | Erlang Module Definition | os(3erl) |
NAME¶
os - Operating System Specific FunctionsDESCRIPTION¶
The functions in this module are operating system specific. Careless use of these functions will result 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 unix:cmd/1; on a Unix
platform they are equivalent.
Examples:
LsOut = os:cmd("ls"), % on unix platform DirOut = os:cmd("dir"), % on Win32 platformNote that in some cases, standard output of a command when called from another program (for example, os:cmd/1) may differ, compared to 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 given its name and a search
path, in the same way as the underlying operating system.
find_executable/1 uses the current execution path (that is, the
environment variable PATH on Unix and Windows).
Path, if given, should conform to the syntax of execution paths on the
operating system. The absolute filename of the executable program Name
is returned, or false if the program was not found.
Returns a list of all environment variables. Each environment variable is given
as a single string on the format "VarName=Value", where
VarName is the name of the variable and Value its value.
Types:
VarName = string()
Value = string()
Returns the Value of the environment variable VarName, or
false if the environment variable is undefined.
Types:
Value = string()
Returns the process identifier of the current Erlang emulator in the format most
commonly used by the operating system environment. Value is returned 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
VxWorks, Value contains the task id (decimal notation) of the Erlang
task. On Windows, the process id as returned by the
GetCurrentProcessId() system call is used.
Types:
VarName = string()
Value = string()
Sets a new Value for the environment variable VarName.
Types:
Timestamp = {MegaSecs, Secs, MicroSecs} =
erlang:timestamp()
MegaSecs = Secs = MicroSecs = integer() >= 0
Returns a tuple in the same format as erlang:now/0. The difference is
that this function returns what the operating system thinks (a.k.a. the wall
clock time) without any attempts at time correction. The result of two
different calls to this function is not guaranteed to be different.
The most obvious use for this function is logging. The tuple can be used
together with the 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 timestamps in high resolution and consistent with
the time in the rest of the operating system.
Example of code formatting a string in the 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]).The module above could be used in the following way:
1> io:format("~s~n",[print_time:format_utc_timestamp()]). 29 Apr 2009 9:55:30.051711
type() -> vxworks | {Osfamily, Osname}
Types:
Osfamily = unix | win32
Osname = atom()
Returns the Osfamily and, in some cases, Osname of the current
operating system.
On Unix, Osname will have same value as uname -s returns, but in
lower case. For example, on Solaris 1 and 2, it will be sunos.
In Windows, Osname will be either nt (on Windows NT), or
windows (on Windows 95).
On VxWorks the OS family alone is returned, that is vxworks.
Note:
Think twice before using this function. Use the filename module if you
want to inspect or build file names in a portable way. Avoid matching on the
Osname atom.
version() -> VersionString | {Major, Minor, Release}
Types:
VersionString = string()
Major = Minor = Release = integer() >= 0
Returns the operating system version. On most systems, this function returns a
tuple, but a string will be returned instead if the system has versions which
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 2.15.1 | Ericsson AB |