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Diffstat (limited to 'lib/kernel/doc/src/os.xml')
| -rw-r--r-- | lib/kernel/doc/src/os.xml | 315 |
1 files changed, 201 insertions, 114 deletions
diff --git a/lib/kernel/doc/src/os.xml b/lib/kernel/doc/src/os.xml index f3a051c989..739ac35d2a 100644 --- a/lib/kernel/doc/src/os.xml +++ b/lib/kernel/doc/src/os.xml @@ -1,23 +1,24 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> - <year>1997</year><year>2012</year> + <year>1997</year><year>2016</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. + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. </legalnotice> @@ -28,178 +29,264 @@ <rev></rev> </header> <module>os</module> - <modulesummary>Operating System Specific Functions</modulesummary> + <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 + <p>The functions in this module are operating system-specific. + Careless use of these functions results 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 + 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> + <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 + <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> + the previous function <c>unix:cmd/1</c>; they are equivalent on a + Unix platform.</p> + <p><em>Examples:</em></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 + <p>Notice 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 + can differ, compared with 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> + <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 + <p>These two functions look up an executable program, with the + specified name and a search path, in the same way as the underlying + OS. <c>find_executable/1</c> uses the current + execution path (that is, the environment variable <c>PATH</c> 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> + <p><c><anno>Path</anno></c>, if specified, is to conform to the syntax + of execution paths on the OS. Returns the absolute filename of the + executable program <c><anno>Name</anno></c>, + or <c>false</c> if the program is not found.</p> </desc> </func> + <func> - <name>getenv() -> [string()]</name> - <fsummary>List all environment variables</fsummary> + <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 + Each environment variable is expressed 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> + <p>If Unicode filename encoding is in effect (see the + <seealso marker="erts:erl#file_name_encoding"><c>erl</c> manual + page</seealso>), the strings can contain characters with + codepoints > 255.</p> </desc> </func> + <func> - <name>getenv(VarName) -> Value | false</name> - <fsummary>Get the value of an environment variable</fsummary> - <type> - <v>VarName = string() </v> - <v>Value = string()</v> - </type> + <name name="getenv" arity="1"/> + <fsummary>Get the value of an environment variable.</fsummary> <desc> - <p>Returns the <c>Value</c> of the environment variable - <c>VarName</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>VarName</c> and - <c>Value</c>) may contain characters with codepoints > 255.</p> + <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 filename encoding is in effect (see the + <seealso marker="erts:erl#file_name_encoding"><c>erl</c> manual + page</seealso>), the strings <c><anno>VarName</anno></c> and + <c><anno>Value</anno></c> can contain characters with + codepoints > 255.</p> </desc> </func> + <func> - <name>getpid() -> Value </name> - <fsummary>Return the process identifier of the emulator process</fsummary> - <type> - <v>Value = string()</v> - </type> + <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 filename encoding is in effect (see the + <seealso marker="erts:erl#file_name_encoding"><c>erl</c> manual + page</seealso>), the strings <c><anno>VarName</anno></c> and + <c><anno>Value</anno></c> can 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>Value</c> is returned as a string containing + in the format most commonly used by the OS environment. + Returns <c><anno>Value</anno></c> 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 VxWorks, <c>Value</c> contains the task id - (decimal notation) of the Erlang task. On Windows, + 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 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"><c>erl</c> manual + page</seealso>), the strings <c><anno>VarName</anno></c> and + <c><anno>Value</anno></c> can contain characters with + codepoints > 255.</p> + <p>On Unix platforms, the environment is set using UTF-8 encoding + if Unicode filename translation is in effect. On Windows, the + environment is set using wide character interfaces.</p> + </desc> + </func> + <func> - <name>putenv(VarName, Value) -> true</name> - <fsummary>Set a new value for an environment variable</fsummary> - <type> - <v>VarName = string() </v> - <v>Value = string()</v> - </type> + <name name="system_time" arity="0"/> + <fsummary>Current OS system time.</fsummary> <desc> - <p>Sets a new <c>Value</c> for the environment variable - <c>VarName</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>VarName</c> and - <c>Value</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> + <p>Returns the 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>timestamp() -> Timestamp</name> - <fsummary>Returna a timestamp from the OS in the erlang:now/0 format</fsummary> - <type> - <v>Timestamp = {MegaSecs, Secs, MicroSecs} = <seealso marker="erts:erlang#type-timestamp">erlang:timestamp()</seealso></v> - <v>MegaSecs = Secs = MicroSecs = integer() >= 0</v> - </type> + <name name="system_time" arity="1"/> + <fsummary>Current OS system time.</fsummary> <desc> - <p>Returns a tuple in the same format as <seealso marker="erts:erlang#now/0">erlang:now/0</seealso>. 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 <em>not</em> guaranteed to be different.</p> - <p>The most obvious use for this function is logging. 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> + <p>Returns the 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>(<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"/> + <fsummary>Current OS system time on the <c>erlang:timestamp/0</c> format.</fsummary> + <type_desc variable="Timestamp">Timestamp = {MegaSecs, Secs, MicroSecs}</type_desc> + <desc> + <p>Returns the current + <seealso marker="erts:time_correction#OS_System_Time">OS system time</seealso> + in the same format as + <seealso marker="erts:erlang#timestamp/0"><c>erlang:timestamp/0</c></seealso>. + The tuple can be used together with function + <seealso marker="stdlib:calendar#now_to_universal_time/1"><c>calendar:now_to_universal_time/1</c></seealso> + or <seealso marker="stdlib:calendar#now_to_local_time/1"><c>calendar:now_to_local_time/1</c></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 time stamps in high resolution and consistent with the + time in the rest of the OS.</p> + <p>Example of code formatting a string in 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), + {{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"}), + "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> + [Day,Mstr,Year,Hour,Minute,Second,Micro]).</code> + <p>This module can be used as follows:</p> + <pre> 1> <input>io:format("~s~n",[print_time:format_utc_timestamp()]).</input> -29 Apr 2009 9:55:30.051711 -</pre> +29 Apr 2009 9:55:30.051711</pre> + <p>OS system time can also be retreived by + <seealso marker="#system_time/0"><c>system_time/0</c></seealso> and + <seealso marker="#system_time/1"><c>system_time/1</c></seealso>.</p> + </desc> + </func> + + <func> + <name name="perf_counter" arity="0"/> + <fsummary>Returns a performance counter</fsummary> + <desc> + <p>Returns the current performance counter value in <c>perf_counter</c> + <seealso marker="erts:erlang#type_time_unit">time unit</seealso>. + This is a highly optimized call that might not be traceable. + </p> + </desc> + </func> + <func> + <name name="perf_counter" arity="1"/> + <fsummary>Returns a performance counter</fsummary> + <desc><p>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 will be converted to the resolution passed as an argument.</p> + <pre>1> <input>T1 = os:perf_counter(1000),receive after 10000 -> ok end,T2 = os:perf_counter(1000).</input> +176525861 +2> <input>T2 - T1.</input> +10004</pre> </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> + <fsummary>Return the OS family and, in some cases, the OS name of the + current OS.</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 + <p>Returns the <c><anno>Osfamily</anno></c> and, in some cases, the + <c><anno>Osname</anno></c> of the current OS.</p> + <p>On Unix, <c><anno>Osname</anno></c> has the 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> - <p>On VxWorks the OS family alone is returned, that is - <c>vxworks</c>.</p> + Solaris 1 and 2, it is <c>sunos</c>.</p> + <p>On Windows, <c><anno>Osname</anno></c> is <c>nt</c>.</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> + <p>Think twice before using this function. Use module + <seealso marker="stdlib:filename"><c>filename</c></seealso> + if you want to inspect or build filenames in a portable way. + Avoid matching on atom <c><anno>Osname</anno></c>.</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"><c>erl</c> manual + page</seealso>), the string <c><anno>VarName</anno></c> can + contain characters with codepoints > 255.</p> + </desc> + </func> + <func> <name name="version" arity="0"/> - <fsummary>Return the Operating System version</fsummary> + <fsummary>Return the OS versions.</fsummary> <desc> - <p>Returns the operating system version. + <p>Returns the OS version. On most systems, this function returns a tuple, but a string - will be returned instead if the system has versions which + is returned instead if the system has versions that cannot be expressed as three numbers.</p> <note> <p>Think twice before using this function. If you still need |