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document udev escaped string in udev(7)
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man/udev.xml
34
man/udev.xml
@ -23,7 +23,8 @@
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<refpurpose>Dynamic device management</refpurpose>
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</refnamediv>
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<refsect1><title>Description</title>
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<refsect1>
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<title>Description</title>
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<para>udev supplies the system software with device events, manages permissions
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of device nodes and may create additional symlinks in the <filename>/dev/</filename>
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directory, or renames network interfaces. The kernel usually just assigns unpredictable
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@ -44,7 +45,8 @@
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sources is provided by the library libudev.</para>
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</refsect1>
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<refsect1><title>Rules Files</title>
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<refsect1>
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<title>Rules Files</title>
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<para>The udev rules are read from the files located in the system rules directories
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<filename>/usr/lib/udev/rules.d</filename> and <filename>/usr/local/lib/udev/rules.d</filename>, the
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volatile runtime directory <filename>/run/udev/rules.d</filename> and the local administration
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@ -68,9 +70,11 @@
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pointing to the device node, or run a specified program as part of
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the event handling.</para>
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<para>A rule consists of a comma-separated list of one or more key-value pairs.
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Each key has a distinct operation, depending on the used operator. Valid
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operators are:</para>
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<para>A rule consists of a comma-separated list of one or more key-operator-value expressions.
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Each expression has a distinct effect, depending on the key and operator used.</para>
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<refsect2>
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<title>Operators</title>
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<variablelist>
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<varlistentry>
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<term><literal>==</literal></term>
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@ -115,7 +119,26 @@
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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<refsect2>
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<title>Values</title>
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<para>Values are written as double quoted strings, such as ("string").
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To include a quotation mark (") in the value, precede it by a backslash (\").
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Any other occurrences of a character followed by a backslash are not further unescaped.
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That is, "\t\n" is treated as four characters:
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backslash, lowercase t, backslash, lowercase n.</para>
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<para>The string can be prefixed with a lowercase e (e"string\n") to mark the string as
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<ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C-style escaped</ulink>.
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For example, e"string\n" is parsed as 7 characters: 6 lowercase letters and a newline.
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This can be useful for writting special characters when a kernel driver requires them.</para>
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<para>Please note that <constant>NUL</constant> is not allowed in either string variant.</para>
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</refsect2>
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<refsect2>
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<title>Keys</title>
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<para>The following key names can be used to match against device properties.
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Some of the keys also match against properties of the parent devices in sysfs,
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not only the device that has generated the event. If multiple keys that match
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@ -789,6 +812,7 @@
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<refsect1>
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