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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 = 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 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 = 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.
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.
If Unicode file name encoding is in effect (see the erl manual page), the strings
may 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 file name encoding is in effect (see the erl manual page), the strings
(both VarName and Value) may 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 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.
putenv(VarName, Value) -> true
Types:
VarName = Value = string()
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.
timestamp() -> Timestamp
Types:
Timestamp = erlang:timestamp()
Timestamp = {MegaSecs, Secs, MicroSecs}
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}
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).
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.
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) may contain characters with codepoints > 255.
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.