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.
Functions
cmd(Command) -> string()
Command = atom() | io_lib:chars()
Executes
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
Name = Filename = string()
find_executable(Name, Path) -> Filename | false
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).
, if given, should conform to the syntax of
execution paths on the operating system. The absolute
filename of the executable program
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
VarName = Value = string()
Returns the
of the environment variable
, or false
if the environment variable
is undefined.
If Unicode file name encoding is in effect (see the erl manual
page), the strings (both
and
) may contain characters with codepoints > 255.
getpid() -> Value
Value = string()
Returns the process identifier of the current Erlang emulator
in the format most commonly used by the operating system
environment.
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
VarName = Value = string()
Sets a new
for the environment variable
.
If Unicode filename encoding is in effect (see the erl manual
page), the strings (both
and
) 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
Timestamp = erlang:timestamp()
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}
Osfamily = unix | win32
Osname = atom()
Returns the
and, in some cases,
of the current operating system.
On Unix,
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,
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
atom.
unsetenv(VarName) -> true
VarName = string()
Deletes the environment variable
.
If Unicode filename encoding is in effect (see the erl manual
page), the string (
) may
contain characters with codepoints > 255.
version() -> VersionString | {Major, Minor, Release}
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.