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 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 = string() | atom()

	      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 platform

	      Note 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 = string()
		     Path = string()
		     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 sys-
	      tem. 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.

       getenv() -> [string()]

	      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.

       getenv(VarName) -> Value | false

	      Types  VarName = string()
		     Value = string()

	      Returns the Value of the environment variable VarName , or false if the environment variable is undefined.

       getpid() -> Value

	      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.

       putenv(VarName, Value) -> true

	      Types  VarName = string()
		     Value = string()

	      Sets a new Value for the environment variable VarName .

       timestamp() -> {MegaSecs, Secs, MicroSecs}

	      Types  MegaSecs = Secs = MicroSecs = int()

	      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() -> {Osfamily, Osname} | Osfamily

	      Types  Osfamily = win32 | unix | vxworks
		     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 match-
       ing on the Osname atom.

       version() -> {Major, Minor, Release} | VersionString

	      Types  Major = Minor = Release = integer()
		     VersionString = string()

	      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.

Ericsson AB							   kernel 2.14.3							  os(3erl)