diff options
Diffstat (limited to 'lib/kernel/doc/src')
| -rw-r--r-- | lib/kernel/doc/src/code.xml | 18 | ||||
| -rw-r--r-- | lib/kernel/doc/src/file.xml | 272 | ||||
| -rw-r--r-- | lib/kernel/doc/src/inet.xml | 60 | ||||
| -rw-r--r-- | lib/kernel/doc/src/inet_res.xml | 2 | ||||
| -rw-r--r-- | lib/kernel/doc/src/net_kernel.xml | 9 | ||||
| -rw-r--r-- | lib/kernel/doc/src/os.xml | 90 |
6 files changed, 282 insertions, 169 deletions
diff --git a/lib/kernel/doc/src/code.xml b/lib/kernel/doc/src/code.xml index c94f612c01..bd95819636 100644 --- a/lib/kernel/doc/src/code.xml +++ b/lib/kernel/doc/src/code.xml @@ -34,26 +34,28 @@ <p>This module contains the interface to the Erlang <em>code server</em>, which deals with the loading of compiled code into a running Erlang runtime system.</p> - <p>The runtime system can be started in <em>embedded</em> or - <em>interactive</em> mode. Which one is decided by command-line + <p>The runtime system can be started in <em>interactive</em> or + <em>embedded</em> mode. Which one is decided by the command-line flag <c>-mode</c>:</p> <pre> % <input>erl -mode interactive</input></pre> <p>The modes are as follows:</p> <list type="bulleted"> <item> - <p>In embedded mode, all code is loaded during system startup - according to the boot script. (Code can also be loaded later - by explicitly ordering the code server to do so).</p> - </item> - <item> <p>In interactive mode, which is default, only some code is loaded - during system startup, basically the modules needed by the runtime + during system startup, basically the modules needed by the runtime system. Other code is dynamically loaded when first referenced. When a call to a function in a certain module is made, and the module is not loaded, the code server searches for and tries to load the module.</p> </item> + <item> + <p>In embedded mode, modules are not auto loaded. Trying to use + a module that has not been loaded results in an error. This mode is + recommended when the boot script loads all modules, as it is + typically done in OTP releases. (Code can still be loaded later + by explicitly ordering the code server to do so).</p> + </item> </list> <p>To prevent accidentally reloading of modules affecting the Erlang runtime system, directories <c>kernel</c>, <c>stdlib</c>, diff --git a/lib/kernel/doc/src/file.xml b/lib/kernel/doc/src/file.xml index b674b3ca93..8477b0e148 100644 --- a/lib/kernel/doc/src/file.xml +++ b/lib/kernel/doc/src/file.xml @@ -33,15 +33,18 @@ <description> <p>This module provides an interface to the file system.</p> - <p>On operating systems with thread support, - file operations can be performed in threads of their own, allowing - other Erlang processes to continue executing in parallel with - the file operations. See command-line flag - <c>+A</c> in <seealso marker="erts:erl"><c>erl(1)</c></seealso>.</p> + <warning> + <p>File operations are only guaranteed to appear atomic when going + through the same file server. A NIF or other OS process may observe + intermediate steps on certain operations on some operating systems, + eg. renaming an existing file on Windows, or + <seealso marker="#write_file_info/2"><c>write_file_info/2</c> + </seealso> on any OS at the time of writing.</p> + </warning> <p>Regarding filename encoding, the Erlang VM can operate in two modes. The current mode can be queried using function - <seealso marker="#native_name_encoding"><c>native_name_encoding/0</c></seealso>. + <seealso marker="#native_name_encoding/0"><c>native_name_encoding/0</c></seealso>. It returns <c>latin1</c> or <c>utf8</c>.</p> <p>In <c>latin1</c> mode, the Erlang VM does not change the @@ -59,7 +62,7 @@ terminal supports UTF-8, otherwise <c>latin1</c>. The default can be overridden using <c>+fnl</c> (to force <c>latin1</c> mode) or <c>+fnu</c> (to force <c>utf8</c> mode) when starting - <seealso marker="erts:erl"><c>erts:erl</c></seealso>.</p> + <seealso marker="erts:erl"><c>erl</c></seealso>.</p> <p>On operating systems with transparent naming, files can be inconsistently named, for example, some files are encoded in UTF-8 while @@ -81,6 +84,16 @@ <p>See also section <seealso marker="stdlib:unicode_usage#notes-about-raw-filenames">Notes About Raw Filenames</seealso> in the STDLIB User's Guide.</p> + <note><p> + File operations used to accept filenames containing + null characters (integer value zero). This caused + the name to be truncated and in some cases arguments + to primitive operations to be mixed up. Filenames + containing null characters inside the filename + are now <em>rejected</em> and will cause primitive + file operations fail. + </p></note> + </description> <datatypes> @@ -96,9 +109,21 @@ </datatype> <datatype> <name name="filename"/> + <desc> + <p> + See also the documentation of the + <seealso marker="#type-name_all"><c>name_all()</c></seealso> type. + </p> + </desc> </datatype> <datatype> <name name="filename_all"/> + <desc> + <p> + See also the documentation of the + <seealso marker="#type-name_all"><c>name_all()</c></seealso> type. + </p> + </desc> </datatype> <datatype> <name name="io_device"/> @@ -112,21 +137,23 @@ <name name="name"/> <desc> <p>If VM is in Unicode filename mode, <c>string()</c> and <c>char()</c> - are allowed to be > 255. + are allowed to be > 255. See also the documentation of the + <seealso marker="#type-name_all"><c>name_all()</c></seealso> type. </p> </desc> </datatype> <datatype> <name name="name_all"/> <desc> - <p>If VM is in Unicode filename mode, <c>string()</c> and <c>char()</c> + <p>If VM is in Unicode filename mode, characters are allowed to be > 255. <c><anno>RawFilename</anno></c> is a filename not subject to Unicode translation, meaning that it can contain characters not conforming to the Unicode encoding expected from the file system (that is, non-UTF-8 characters although the VM is started - in Unicode filename mode). + in Unicode filename mode). Null characters (integer value zero) + are <em>not</em> allowed in filenames (not even at the end). </p> </desc> </datatype> @@ -1407,8 +1434,12 @@ f.txt: {person, "kalle", 25}. which is 1970-01-01 00:00 UTC.</p></item> </taglist> <p>Default is <c>{time, local}</c>.</p> - <p>If the option <c>raw</c> is set, the file server is not called - and only information about local files is returned.</p> + <p>If the option <c>raw</c> is set, the file server is not called and + only information about local files is returned. Note that this will + break this module's atomicity guarantees as it can race with a + concurrent call to + <seealso marker="#write_file_info/2"><c>write_file_info/1,2</c> + </seealso></p> <note> <p>As file times are stored in POSIX time on most OS, it is faster to query file information with option <c>posix</c>.</p> @@ -1656,8 +1687,12 @@ f.txt: {person, "kalle", 25}. except that if <c><anno>Name</anno></c> is a symbolic link, information about the link is returned in the <c>file_info</c> record and the <c>type</c> field of the record is set to <c>symlink</c>.</p> - <p>If the option <c>raw</c> is set, the file server is not called - and only information about local files is returned.</p> + <p>If the option <c>raw</c> is set, the file server is not called and + only information about local files is returned. Note that this will + break this module's atomicity guarantees as it can race with a + concurrent call to + <seealso marker="#write_file_info/2"><c>write_file_info/1,2</c> + </seealso></p> <p>If <c><anno>Name</anno></c> is not a symbolic link, this function returns the same result as <c>read_file_info/1</c>. On platforms that do not support symbolic links, this function @@ -1795,24 +1830,16 @@ f.txt: {person, "kalle", 25}. <p>The file used must be opened using the <c>raw</c> flag, and the process calling <c>sendfile</c> must be the controlling process of the socket. See <seealso marker="gen_tcp#controlling_process-2"><c>gen_tcp:controlling_process/2</c></seealso>.</p> - <p>If the OS used does not support <c>sendfile</c>, an Erlang fallback - using - <seealso marker="#read/2"><c>read/2</c></seealso> and - <seealso marker="gen_tcp#send/2"><c>gen_tcp:send/2</c></seealso> is used.</p> + <p>If the OS used does not support non-blocking <c>sendfile</c>, an + Erlang fallback using <seealso marker="#read/2"><c>read/2</c></seealso> + and <seealso marker="gen_tcp#send/2"><c>gen_tcp:send/2</c></seealso> is + used.</p> <p>The option list can contain the following options:</p> <taglist> <tag><c>chunk_size</c></tag> <item><p>The chunk size used by the Erlang fallback to send data. If using the fallback, set this to a value that comfortably fits in the systems memory. Default is 20 MB.</p></item> - <tag><c>use_threads</c></tag> - <item><p>Instructs the emulator to use the <c>async</c> thread pool for the - <c>sendfile</c> system call. This can be useful if the OS you are running - on does not properly support non-blocking <c>sendfile</c> calls. Notice that - using <c>async</c> threads potentially makes your system vulnerable to slow - client attacks. If set to <c>true</c> and no <c>async</c> threads are available, - the <c>sendfile</c> call returns <c>{error,einval}</c>. - Introduced in Erlang/OTP 17.0. Default is <c>false</c>.</p></item> </taglist> </desc> </func> @@ -1825,7 +1852,7 @@ f.txt: {person, "kalle", 25}. <p>The functions in the module <c>file</c> usually treat binaries as raw filenames, that is, they are passed "as is" even when the encoding of the binary does not agree with - <seealso marker="#native_name_encoding"><c>native_name_encoding()</c></seealso>. + <seealso marker="#native_name_encoding/0"><c>native_name_encoding()</c></seealso>. However, this function expects binaries to be encoded according to the value returned by <c>native_name_encoding()</c>.</p> <p>Typical error reasons are:</p> @@ -2117,144 +2144,77 @@ f.txt: {person, "kalle", 25}. <section> <title>Performance</title> - <p>Some operating system file operations, for example, a - <c>sync/1</c> or <c>close/1</c> on a huge file, can block their - calling thread for seconds. If this affects the emulator main - thread, the response time is no longer in the order of - milliseconds, depending on the definition of "soft" in soft - real-time system.</p> - <p>If the device driver thread pool is active, file operations are - done through those threads instead, so the emulator can go on - executing Erlang processes. Unfortunately, the time for serving a - file operation increases because of the extra scheduling required - from the operating system.</p> - <p>If the device driver thread pool is disabled or of size 0, large - file reads and writes are segmented into many smaller, which - enable the emulator to serve other processes during the file - operation. This has the same effect as when using the thread - pool, but with larger overhead. Other file operations, for - example, <c>sync/1</c> or <c>close/1</c> on a huge file, still are - a problem.</p> - <p>For increased performance, raw files are recommended. Raw files - use the file system of the host machine of the node.</p> + <p>For increased performance, raw files are recommended.</p> + <p>A normal file is really a process so it can be used as an I/O + device (see <seealso marker="stdlib:io"><c>io</c></seealso>). + Therefore, when data is written to a normal file, the sending of the + data to the file process, copies all data that are not binaries. Opening + the file in binary mode and writing binaries is therefore recommended. + If the file is opened on another node, or if the file server runs as + slave to the file server of another node, also binaries are copied.</p> <note> - <p> - For normal files (non-raw), the file server is used to find the files, - and if the node is running its file server as slave to the file server - of another node, and the other node runs on some other host machine, - they can have different file systems. - However, this is seldom a problem.</p> + <p>Raw files use the file system of the host machine of the node. + For normal files (non-raw), the file server is used to find the files, + and if the node is running its file server as slave to the file server + of another node, and the other node runs on some other host machine, + they can have different file systems. + However, this is seldom a problem.</p> </note> - <p>A normal file is really a process so it can be used as an I/O - device (see - <seealso marker="stdlib:io"><c>io</c></seealso>). - Therefore, when data is written to a - normal file, the sending of the data to the file process, copies - all data that are not binaries. Opening the file in binary mode - and writing binaries is therefore recommended. If the file is - opened on another node, or if the file server runs as slave to - the file server of another node, also binaries are copied.</p> - <p>Caching data to reduce the number of file operations, or rather - the number of calls to the file driver, generally increases - performance. The following function writes 4 MBytes in 23 - seconds when tested:</p> + <p><seealso marker="#open/2"><c>open/2</c></seealso> can be given the + options <c>delayed_write</c> and <c>read_ahead</c> to turn on caching, + which will reduce the number of operating system calls and greatly + improve performance for small reads and writes. However, the overhead + won't disappear completely and it's best to keep the number of file + operations to a minimum. As a contrived example, the following function + writes 4MB in 2.5 seconds when tested:</p> + <code type="none"><![CDATA[ -create_file_slow(Name, N) when integer(N), N >= 0 -> - {ok, FD} = file:open(Name, [raw, write, delayed_write, binary]), - ok = create_file_slow(FD, 0, N), - ok = ?FILE_MODULE:close(FD), - ok. - -create_file_slow(FD, M, M) -> +create_file_slow(Name) -> + {ok, Fd} = file:open(Name, [raw, write, delayed_write, binary]), + create_file_slow_1(Fd, 4 bsl 20), + file:close(Fd). + +create_file_slow_1(_Fd, 0) -> ok; -create_file_slow(FD, M, N) -> - ok = file:write(FD, <<M:32/unsigned>>), - create_file_slow(FD, M+1, N).]]></code> +create_file_slow_1(Fd, M) -> + ok = file:write(Fd, <<0>>), + create_file_slow_1(Fd, M - 1).]]></code> + + <p>The following functionally equivalent code writes 128 bytes per call + to <seealso marker="#write/2"><c>write/2</c></seealso> and so does the + same work in 0.08 seconds, which is roughly 30 times faster:</p> - <p>The following, functionally equivalent, function collects 1024 - entries into a list of 128 32-byte binaries before each call to - <seealso marker="#write/2"><c>write/2</c></seealso> and so - does the same work in 0.52 seconds, - which is 44 times faster:</p> <code type="none"><![CDATA[ -create_file(Name, N) when integer(N), N >= 0 -> - {ok, FD} = file:open(Name, [raw, write, delayed_write, binary]), - ok = create_file(FD, 0, N), - ok = ?FILE_MODULE:close(FD), +create_file(Name) -> + {ok, Fd} = file:open(Name, [raw, write, delayed_write, binary]), + create_file_1(Fd, 4 bsl 20), + file:close(Fd), ok. - -create_file(FD, M, M) -> + +create_file_1(_Fd, 0) -> ok; -create_file(FD, M, N) when M + 1024 =< N -> - create_file(FD, M, M + 1024, []), - create_file(FD, M + 1024, N); -create_file(FD, M, N) -> - create_file(FD, M, N, []). - -create_file(FD, M, M, R) -> - ok = file:write(FD, R); -create_file(FD, M, N0, R) when M + 8 =< N0 -> - N1 = N0-1, N2 = N0-2, N3 = N0-3, N4 = N0-4, - N5 = N0-5, N6 = N0-6, N7 = N0-7, N8 = N0-8, - create_file(FD, M, N8, - [<<N8:32/unsigned, N7:32/unsigned, - N6:32/unsigned, N5:32/unsigned, - N4:32/unsigned, N3:32/unsigned, - N2:32/unsigned, N1:32/unsigned>> | R]); -create_file(FD, M, N0, R) -> - N1 = N0-1, - create_file(FD, M, N1, [<<N1:32/unsigned>> | R]).]]></code> +create_file_1(Fd, M) when M >= 128 -> + ok = file:write(Fd, <<0:(128)/unit:8>>), + create_file_1(Fd, M - 128); +create_file_1(Fd, M) -> + ok = file:write(Fd, <<0:(M)/unit:8>>), + create_file_1(Fd, M - 1).]]></code> - <note> - <p>Trust only your own benchmarks. If the list length in - <c>create_file/2</c> above is increased, it runs slightly - faster, but consumes more memory and causes more memory - fragmentation. How much this affects your application is - something that this simple benchmark cannot predict.</p> - <p>If the size of each binary is increased to 64 bytes, it - also runs slightly faster, but the code is then twice as clumsy. - In the current implementation, binaries larger than 64 bytes are - stored in memory common to all processes and not copied when - sent between processes, while these smaller binaries are stored - on the process heap and copied when sent like any other term.</p> - <p>So, with a binary size of 68 bytes, <c>create_file/2</c> runs - 30 percent slower than with 64 bytes, and causes much more - memory fragmentation. Notice that if the binaries were to be sent - between processes (for example, a non-raw file), the results - would probably be completely different.</p> - </note> - <p>A raw file is really a port. When writing data to a port, it is - efficient to write a list of binaries. It is not needed to - flatten a deep list before writing. On Unix hosts, scatter output, - which writes a set of buffers in one operation, is used when - possible. In this way <c>write(FD, [Bin1, Bin2 | Bin3])</c> - writes the contents of the binaries without copying the data - at all, except for perhaps deep down in the operating system - kernel.</p> - <p>For raw files, <c>pwrite/2</c> and <c>pread/2</c> are - efficiently implemented. The file driver is called only once for - the whole operation, and the list iteration is done in the file - driver.</p> - <p>The options <c>delayed_write</c> and <c>read_ahead</c> to - <seealso marker="#open/2"><c>open/2</c></seealso> - make the file driver cache data to reduce - the number of operating system calls. The function - <c>create_file/2</c> in the recent example takes 60 seconds - without option <c>delayed_write</c>, which is 2.6 - times slower.</p> - <p>As a bad example, <c>create_file_slow/2</c> - without options <c>raw</c>, <c>binary</c>, and <c>delayed_write</c>, - meaning it calls <c>open(Name, [write])</c>, needs - 1 min 20 seconds for the job, which is 3.5 times slower than - the first example, and 150 times slower than the optimized - <c>create_file/2</c>.</p> - <warning> - <p>If an error occurs when accessing an open file with module - <seealso marker="stdlib:io"><c>io</c></seealso>, - the process handling the file exits. The dead - file process can hang if a process tries to access it later. - This will be fixed in a future release.</p> - </warning> + <p>When writing data it's generally more efficient to write a list of + binaries rather than a list of integers. It is not needed to + flatten a deep list before writing. On Unix hosts, scatter output, + which writes a set of buffers in one operation, is used when + possible. In this way <c>write(FD, [Bin1, Bin2 | Bin3])</c> + writes the contents of the binaries without copying the data + at all, except for perhaps deep down in the operating system + kernel.</p> + <warning> + <p>If an error occurs when accessing an open file with module + <seealso marker="stdlib:io"><c>io</c></seealso>, the process + handling the file exits. The dead file process can hang if a process + tries to access it later. This will be fixed in a future release. + </p> + </warning> </section> <section> diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml index 169a76463b..abb045b744 100644 --- a/lib/kernel/doc/src/inet.xml +++ b/lib/kernel/doc/src/inet.xml @@ -197,6 +197,9 @@ fe80::204:acff:fe17:bf38 <datatype> <name name="address_family"/> </datatype> + <datatype> + <name name="socket_protocol"/> + </datatype> </datatypes> <funcs> @@ -461,6 +464,61 @@ get_tcpi_sacked(Sock) -> </func> <func> + <name name="i" arity="0" /> + <name name="i" arity="1" /> + <name name="i" arity="2" /> + <fsummary>Displays information and statistics about sockets on the terminal</fsummary> + <desc> + <p> + Lists all TCP, UDP and SCTP sockets, including those that the Erlang runtime system uses as well as + those created by the application. + </p> + <p> + The following options are available: + </p> + + <taglist> + <tag><c>port</c></tag> + <item> + <p>The internal index of the port.</p> + </item> + <tag><c>module</c></tag> + <item> + <p>The callback module of the socket.</p> + </item> + <tag><c>recv</c></tag> + <item> + <p>Number of bytes received by the socket.</p> + </item> + <tag><c>sent</c></tag> + <item> + <p>Number of bytes sent from the socket.</p> + </item> + <tag><c>owner</c></tag> + <item> + <p>The socket owner process.</p> + </item> + <tag><c>local_address</c></tag> + <item> + <p>The local address of the socket.</p> + </item> + <tag><c>foreign_address</c></tag> + <item> + <p>The address and port of the other end of the connection.</p> + </item> + <tag><c>state</c></tag> + <item> + <p>The connection state.</p> + </item> + <tag><c>type</c></tag> + <item> + <p>STREAM or DGRAM or SEQPACKET.</p> + </item> + </taglist> + </desc> + </func> + + <func> <name name="ntoa" arity="1" /> <fsummary>Convert IPv6/IPV4 address to ASCII.</fsummary> <desc> @@ -1214,7 +1272,7 @@ inet:setopts(Sock,[{raw,6,8,<<30:32/native>>}]),]]></code> For one-to-many style sockets, the special value <c>0</c> is defined to mean that the returned addresses must be without any particular association. - How different SCTP implementations interprets this varies somewhat. + How different SCTP implementations interpret this varies somewhat. </p> </desc> </func> diff --git a/lib/kernel/doc/src/inet_res.xml b/lib/kernel/doc/src/inet_res.xml index 4ada4203c0..3454e3c6f9 100644 --- a/lib/kernel/doc/src/inet_res.xml +++ b/lib/kernel/doc/src/inet_res.xml @@ -130,7 +130,7 @@ dns_header() = DnsHeader inet_dns:header(DnsHeader) -> [ {id, integer()} | {qr, boolean()} - | {opcode, 'query' | iquery | status | integer()} + | {opcode, query | iquery | status | integer()} | {aa, boolean()} | {tc, boolean()} | {rd, boolean()} diff --git a/lib/kernel/doc/src/net_kernel.xml b/lib/kernel/doc/src/net_kernel.xml index 0b94fc0fa6..a30d28d55a 100644 --- a/lib/kernel/doc/src/net_kernel.xml +++ b/lib/kernel/doc/src/net_kernel.xml @@ -56,7 +56,7 @@ $ <input>erl -sname foobar</input></pre> <p>Normally, connections are established automatically when another node is referenced. This functionality can be disabled by setting Kernel configuration parameter - <c>dist_auto_connect</c> to <c>false</c>, see + <c>dist_auto_connect</c> to <c>never</c>, see <seealso marker="kernel_app"><c>kernel(6)</c></seealso>. In this case, connections must be established explicitly by calling <seealso marker="#connect_node/1"><c>connect_node/1</c></seealso>.</p> @@ -230,7 +230,12 @@ $ <input>erl -sname foobar</input></pre> <item> <p>The tuple <c>{nodedown_reason, Reason}</c> is included in <c>InfoList</c> in <c>nodedown</c> messages.</p> - <p><c>Reason</c> can be any of the following:</p> + <p> + <c>Reason</c> can, depending on which + distribution module or process that is used be any term, + but for the standard TCP distribution module it is + any of the following: + </p> <taglist> <tag><c>connection_setup_failed</c></tag> <item><p>The connection setup failed (after <c>nodeup</c> diff --git a/lib/kernel/doc/src/os.xml b/lib/kernel/doc/src/os.xml index 7ce2f54542..ef416ed233 100644 --- a/lib/kernel/doc/src/os.xml +++ b/lib/kernel/doc/src/os.xml @@ -36,11 +36,85 @@ 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> + + <note> + <p> + File operations used to accept filenames containing + null characters (integer value zero). This caused + the name to be truncated and in some cases arguments + to primitive operations to be mixed up. Filenames + containing null characters inside the filename + are now <em>rejected</em> and will cause primitive + file operations to fail. + </p> + <p> + Also environment variable operations used to accept + names and values of environment variables containing + null characters (integer value zero). This caused + operations to silently produce erroneous results. + Environment variable names and values containing + null characters inside the name or value are now + <em>rejected</em> and will cause environment variable + operations to fail. + </p> + </note> </description> <datatypes> <datatype> + <name name="env_var_name"/> + <desc> + <p>A string containing valid characters on the specific + OS for environment variable names using + <seealso marker="file#native_name_encoding/0"><c>file:native_name_encoding()</c></seealso> + encoding. Note that specifically null characters (integer + value zero) and <c>$=</c> characters are not allowed. + However, note that not all invalid characters necessarily + will cause the primitiv operations to fail, but may instead + produce invalid results. + </p> + </desc> + </datatype> + <datatype> + <name name="env_var_value"/> + <desc> + <p>A string containing valid characters on the specific + OS for environment variable values using + <seealso marker="file#native_name_encoding/0"><c>file:native_name_encoding()</c></seealso> + encoding. Note that specifically null characters (integer + value zero) are not allowed. However, note that not all + invalid characters necessarily will cause the primitiv + operations to fail, but may instead produce invalid results. + </p> + </desc> + </datatype> + <datatype> + <name name="env_var_name_value"/> + <desc> + <p> + Assuming that environment variables has been correctly + set, a strings containing valid characters on the specific + OS for environment variable names and values using + <seealso marker="file#native_name_encoding/0"><c>file:native_name_encoding()</c></seealso> + encoding. The first <c>$=</c> characters appearing in + the string separates environment variable name (on the + left) from environment variable value (on the right). + </p> + </desc> + </datatype> + <datatype> <name name="os_command"/> + <desc> + <p>All characters needs to be valid characters on the + specific OS using + <seealso marker="file#native_name_encoding/0"><c>file:native_name_encoding()</c></seealso> + encoding. Note that specifically null characters (integer + value zero) are not allowed. However, note that not all + invalid characters not necessarily will cause + <seealso marker="#cmd/1"><c>os:cmd/1</c></seealso> + to fail, but may instead produce invalid results. + </p> + </desc> </datatype> <datatype> <name name="os_command_opts"/> @@ -65,8 +139,13 @@ <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, + target OS, captures the standard output of the command, and returns this result as a string.</p> + <warning><p>Previous implementation used to allow all characters + as long as they were integer values greater than or equal to zero. + This sometimes lead to unwanted results since null characters + (integer value zero) often are interpreted as string termination. The + current implementation rejects these.</p></warning> <p><em>Examples:</em></p> <code type="none"> LsOut = os:cmd("ls"), % on unix platform @@ -185,6 +264,15 @@ DirOut = os:cmd("dir"), % on Win32 platform</code> <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> + <note> + <p> + <c><anno>VarName</anno></c> is not allowed to contain + an <c>$=</c> character. Previous implementations used + to just let the <c>$=</c> character through which + silently caused erroneous results. Current implementation + will instead throw a <c>badarg</c> exception. + </p> + </note> </desc> </func> |