os

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os Operating System Specific Functions

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.

Execute a command in a shell of the target OS

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.

Absolute filename of a program

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.

List all environment variables

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.

If Unicode file name encoding is in effect (see the erl manual page), the strings may contain characters with codepoints > 255.

Get the value of an environment variable

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

If Unicode file name encoding is in effect (see the erl manual page), the strings (both VarName and Value) may contain characters with codepoints > 255.

Get the value of an environment variable

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

If Unicode file name encoding is in effect (see the erl manual page), the strings (both VarName and Value) may contain characters with codepoints > 255.

Return the process identifier of the emulator process

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 Windows, the process id as returned by the GetCurrentProcessId() system call is used.

Set a new value for an environment variable

Sets a new Value for the environment variable VarName.

If Unicode filename encoding is in effect (see the erl manual page), the strings (both VarName and Value) may contain characters with codepoints > 255.

On Unix platforms, the environment will be set using UTF-8 encoding if Unicode file name translation is in effect. On Windows the environment is set using wide character interfaces.

Current OS system time

Returns current OS system time in native time unit.

This time is not a monotonically increasing time.

Current OS system time

Returns 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).

This time is not a monotonically increasing time.

Current OS system time on the erlang:timestamp/0 format Timestamp = {MegaSecs, Secs, MicroSecs}

Returns current OS system time in the same format as erlang:timestamp/0. 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

OS system time can also be retreived by os:system_time/0, and os:system_time/1.

Returns a performance counter

Returns the current performance counter value in perf_counter time unit. This is a highly optimized call that might not be traceable.

Returns a performance counter

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 till 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

Return the OS family and, in some cases, OS name of the current operating system

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).

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.

Delete an environment variable

Deletes the environment variable VarName.

If Unicode filename encoding is in effect (see the erl manual page), the string (VarName) may contain characters with codepoints > 255.

Return the Operating System version

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.

Think twice before using this function. If you still need to use it, always call os:type() first.