diff options
Diffstat (limited to 'lib/kernel/doc/src/os.xml')
| -rw-r--r-- | lib/kernel/doc/src/os.xml | 131 |
1 files changed, 126 insertions, 5 deletions
diff --git a/lib/kernel/doc/src/os.xml b/lib/kernel/doc/src/os.xml index 0e9add4161..ef416ed233 100644 --- a/lib/kernel/doc/src/os.xml +++ b/lib/kernel/doc/src/os.xml @@ -36,19 +36,116 @@ 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"/> + <desc> + <p>Options for <seealso marker="#cmd/2"><c>os:cmd/2</c></seealso></p> + <taglist> + <tag><c>max_size</c></tag> + <item> + <p>The maximum size of the data returned by the <c>os:cmd</c> call. + See the <seealso marker="#cmd/2"><c>os:cmd/2</c></seealso> + documentation for more details.</p> + </item> + </taglist> + </desc> + </datatype> + </datatypes> + <funcs> <func> <name name="cmd" arity="1"/> + <name name="cmd" arity="2"/> <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 function <c>unix:cmd/1</c>; they are equivalent on a - Unix platform.</p> + 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 @@ -57,6 +154,21 @@ DirOut = os:cmd("dir"), % on Win32 platform</code> called from another program (for example, <c>os:cmd/1</c>) can differ, compared with the standard output of the command when called directly from an OS command shell.</p> + <p><c>os:cmd/2</c> was added in kernel-5.5 (OTP-20.2.1). It makes it + possible to pass an options map as the second argument in order to + control the behaviour of <c>os:cmd</c>. The possible options are: + </p> + <taglist> + <tag><c>max_size</c></tag> + <item> + <p>The maximum size of the data returned by the <c>os:cmd</c> call. + This option is a safety feature that should be used when the command + executed can return a very large, possibly infinite, result.</p> + <code type="none"> +> os:cmd("cat /dev/zero", #{ max_size => 20 }). +[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]</code> + </item> + </taglist> </desc> </func> @@ -152,6 +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> |