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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.