<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> <year>1997</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/. Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License. </legalnotice> <title>os</title> <prepared></prepared> <docno></docno> <date></date> <rev></rev> </header> <module>os</module> <modulesummary>Operating System Specific Functions</modulesummary> <description> <p>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.</p> </description> <funcs> <func> <name name="cmd" arity="1"/> <fsummary>Execute a command in a shell of the target OS</fsummary> <desc> <p>Executes <c><anno>Command</anno></c> 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 <c>unix:cmd/1</c>; on a Unix platform they are equivalent.</p> <p>Examples:</p> <code type="none"> LsOut = os:cmd("ls"), % on unix platform DirOut = os:cmd("dir"), % on Win32 platform</code> <p>Note that in some cases, standard output of a command when called from another program (for example, <c>os:cmd/1</c>) may differ, compared to the standard output of the command when called directly from an OS command shell.</p> </desc> </func> <func> <name name="find_executable" arity="1"/> <name name="find_executable" arity="2"/> <fsummary>Absolute filename of a program</fsummary> <desc> <p>These two functions look up an executable program given its name and a search path, in the same way as the underlying operating system. <c>find_executable/1</c> uses the current execution path (that is, the environment variable PATH on Unix and Windows).</p> <p><c><anno>Path</anno></c>, if given, should conform to the syntax of execution paths on the operating system. The absolute filename of the executable program <c><anno>Name</anno></c> is returned, or <c>false</c> if the program was not found.</p> </desc> </func> <func> <name name="getenv" arity="0"/> <fsummary>List all environment variables</fsummary> <desc> <p>Returns a list of all environment variables. Each environment variable is given as a single string on the format <c>"VarName=Value"</c>, where <c>VarName</c> is the name of the variable and <c>Value</c> its value.</p> <p>If Unicode file name encoding is in effect (see the <seealso marker="erts:erl#file_name_encoding">erl manual page</seealso>), the strings may contain characters with codepoints > 255.</p> </desc> </func> <func> <name name="getenv" arity="1"/> <fsummary>Get the value of an environment variable</fsummary> <desc> <p>Returns the <c><anno>Value</anno></c> of the environment variable <c><anno>VarName</anno></c>, or <c>false</c> if the environment variable is undefined.</p> <p>If Unicode file name encoding is in effect (see the <seealso marker="erts:erl#file_name_encoding">erl manual page</seealso>), the strings (both <c><anno>VarName</anno></c> and <c><anno>Value</anno></c>) may contain characters with codepoints > 255.</p> </desc> </func> <func> <name name="getenv" arity="2"/> <fsummary>Get the value of an environment variable</fsummary> <desc> <p>Returns the <c><anno>Value</anno></c> of the environment variable <c><anno>VarName</anno></c>, or <c>DefaultValue</c> if the environment variable is undefined.</p> <p>If Unicode file name encoding is in effect (see the <seealso marker="erts:erl#file_name_encoding">erl manual page</seealso>), the strings (both <c><anno>VarName</anno></c> and <c><anno>Value</anno></c>) may contain characters with codepoints > 255.</p> </desc> </func> <func> <name name="getpid" arity="0"/> <fsummary>Return the process identifier of the emulator process</fsummary> <desc> <p>Returns the process identifier of the current Erlang emulator in the format most commonly used by the operating system environment. <c><anno>Value</anno></c> is returned as a string containing the (usually) numerical identifier for a process. On Unix, this is typically the return value of the <c>getpid()</c> system call. On Windows, the process id as returned by the <c>GetCurrentProcessId()</c> system call is used.</p> </desc> </func> <func> <name name="putenv" arity="2"/> <fsummary>Set a new value for an environment variable</fsummary> <desc> <p>Sets a new <c><anno>Value</anno></c> for the environment variable <c><anno>VarName</anno></c>.</p> <p>If Unicode filename encoding is in effect (see the <seealso marker="erts:erl#file_name_encoding">erl manual page</seealso>), the strings (both <c><anno>VarName</anno></c> and <c><anno>Value</anno></c>) may contain characters with codepoints > 255.</p> <p>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.</p> </desc> </func> <func> <name name="system_time" arity="0"/> <fsummary>Current OS system time</fsummary> <desc> <p>Returns current <seealso marker="erts:time_correction#OS_System_Time">OS system time</seealso> in <c>native</c> <seealso marker="erts:erlang#type_time_unit">time unit</seealso>.</p> <note><p>This time is <em>not</em> a monotonically increasing time.</p></note> </desc> </func> <func> <name name="system_time" arity="1"/> <fsummary>Current OS system time</fsummary> <desc> <p>Returns current <seealso marker="erts:time_correction#OS_System_Time">OS system time</seealso> converted into the <c><anno>Unit</anno></c> passed as argument.</p> <p>Calling <c>os:system_time(<anno>Unit</anno>)</c> is equivalent to: <seealso marker="erts:erlang#convert_time_unit/3"><c>erlang:convert_time_unit</c></seealso><c>(</c><seealso marker="#system_time/0"><c>os:system_time()</c></seealso><c>, native, <anno>Unit</anno>)</c>.</p> <note><p>This time is <em>not</em> a monotonically increasing time.</p></note> </desc> </func> <func> <name name="timestamp" arity="0"/> <type_desc variable="Timestamp">Timestamp = {MegaSecs, Secs, MicroSecs}</type_desc> <fsummary>Current OS system time on the erlang:timestamp/0 format</fsummary> <desc> <p>Returns current <seealso marker="erts:time_correction#OS_System_Time">OS system time</seealso> in the same format as <seealso marker="erts:erlang#timestamp/0">erlang:timestamp/0</seealso>. The tuple can be used together with the function <seealso marker="stdlib:calendar#now_to_universal_time/1">calendar:now_to_universal_time/1</seealso> or <seealso marker="stdlib:calendar#now_to_local_time/1">calendar:now_to_local_time/1</seealso> to get calendar time. Using the calendar time together with the <c>MicroSecs</c> 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.</p> <p>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:</p> <code> -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]). </code> <p>The module above could be used in the following way:</p> <pre> 1> <input>io:format("~s~n",[print_time:format_utc_timestamp()]).</input> 29 Apr 2009 9:55:30.051711 </pre> <p>OS system time can also be retreived by <c><seealso marker="#system_time/0"><c>os:system_time/0</c></seealso></c>, and <seealso marker="#system_time/1"><c>os:system_time/1</c></seealso>.</p> </desc> </func> <func> <name name="type" arity="0"/> <fsummary>Return the OS family and, in some cases, OS name of the current operating system</fsummary> <desc> <p>Returns the <c><anno>Osfamily</anno></c> and, in some cases, <c><anno>Osname</anno></c> of the current operating system.</p> <p>On Unix, <c><anno>Osname</anno></c> will have same value as <c>uname -s</c> returns, but in lower case. For example, on Solaris 1 and 2, it will be <c>sunos</c>.</p> <p>In Windows, <c><anno>Osname</anno></c> will be either <c>nt</c> (on Windows NT), or <c>windows</c> (on Windows 95).</p> <note> <p>Think twice before using this function. Use the <c>filename</c> module if you want to inspect or build file names in a portable way. Avoid matching on the <c><anno>Osname</anno></c> atom.</p> </note> </desc> </func> <func> <name name="unsetenv" arity="1"/> <fsummary>Delete an environment variable</fsummary> <desc> <p>Deletes the environment variable <c><anno>VarName</anno></c>.</p> <p>If Unicode filename encoding is in effect (see the <seealso marker="erts:erl#file_name_encoding">erl manual page</seealso>), the string (<c><anno>VarName</anno></c>) may contain characters with codepoints > 255.</p> </desc> </func> <func> <name name="version" arity="0"/> <fsummary>Return the Operating System version</fsummary> <desc> <p>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.</p> <note> <p>Think twice before using this function. If you still need to use it, always <c>call os:type()</c> first.</p> </note> </desc> </func> </funcs> </erlref>