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Diffstat (limited to 'lib/kernel/doc/src/os.xml')
| -rw-r--r-- | lib/kernel/doc/src/os.xml | 259 |
1 files changed, 150 insertions, 109 deletions
diff --git a/lib/kernel/doc/src/os.xml b/lib/kernel/doc/src/os.xml index 682d4a2eac..739ac35d2a 100644 --- a/lib/kernel/doc/src/os.xml +++ b/lib/kernel/doc/src/os.xml @@ -4,7 +4,7 @@ <erlref> <header> <copyright> - <year>1997</year><year>2013</year> + <year>1997</year><year>2016</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -29,97 +29,107 @@ <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 name="getenv" arity="0"/> - <fsummary>List all environment variables</fsummary> + <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 name="getenv" arity="1"/> - <fsummary>Get the value of an environment variable</fsummary> + <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> + <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 name="getenv" arity="2"/> - <fsummary>Get the value of an environment variable</fsummary> + <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> + <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> + <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 + 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 Windows, @@ -127,125 +137,156 @@ DirOut = os:cmd("dir"), % on Win32 platform</code> system call is used.</p> </desc> </func> + <func> <name name="putenv" arity="2"/> - <fsummary>Set a new value for an environment variable</fsummary> + <fsummary>Set a new value for an environment variable.</fsummary> <desc> - <p>Sets a new <c><anno>Value</anno></c> for the environment variable + <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">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> + <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 name="system_time" arity="0"/> - <fsummary>Current OS system time</fsummary> + <fsummary>Current OS system time.</fsummary> <desc> - <p>Returns current + <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> + <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> + <fsummary>Current OS system time.</fsummary> <desc> - <p>Returns current + <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><c>(</c><seealso marker="#system_time/0"><c>os:system_time()</c></seealso><c>, + <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> + <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 erlang:timestamp/0 format</fsummary> + <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 current + <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">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> + 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>os:system_time/0</c></seealso>, - and <seealso marker="#system_time/1"><c>os:system_time/1</c></seealso>.</p> + <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> + 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> + <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> + <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 |