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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_journal_add_match" xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_journal_add_match</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_journal_add_match</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_journal_add_match</refname>
+ <refname>sd_journal_add_disjunction</refname>
+ <refname>sd_journal_add_conjunction</refname>
+ <refname>sd_journal_flush_matches</refname>
+ <refpurpose>Add or remove entry matches</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_add_match</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const void *<parameter>data</parameter></paramdef>
+ <paramdef>size_t <parameter>size</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_add_disjunction</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_add_conjunction</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>void <function>sd_journal_flush_matches</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_journal_add_match()</function> adds a match by
+ which to filter the entries of the journal file. Matches applied
+ with this call will filter what can be iterated through and read
+ from the journal file via calls like
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ and
+ <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+ Parameter <parameter>data</parameter> must be of the form
+ <literal><replaceable>FIELD</replaceable>=<replaceable>value</replaceable></literal>,
+ where the <replaceable>FIELD</replaceable> part is a short uppercase string consisting only
+ of 0–9, A–Z and the underscore; it may not begin with two underscores or be the empty
+ string. The <replaceable>value</replaceable> part may be anything, including binary. Parameter
+ <parameter>size</parameter> specifies the number of bytes in <parameter>data</parameter>
+ (i.e. the length of <replaceable>FIELD</replaceable>, plus one, plus the length of
+ <replaceable>value</replaceable>). Parameter <parameter>size</parameter> may also be
+ specified as <constant>0</constant>, in which case <parameter>data</parameter>
+ must be a <constant>NUL</constant>-terminated string, and the bytes before the terminating
+ zero are used as the match.</para>
+
+ <para>If a match is applied, only entries with this field set
+ will be iterated. Multiple matches may be active at the same time:
+ If they apply to different fields, only entries with both fields
+ set like this will be iterated. If they apply to the same fields,
+ only entries where the field takes one of the specified values
+ will be iterated. Well known fields are documented in
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+ Whenever a new match is added the current entry position is reset,
+ and
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ (or a similar call) needs to be called before entries can be read
+ again.</para>
+
+ <para><function>sd_journal_add_disjunction()</function> may be
+ used to insert a disjunction (i.e. logical OR) in the match list.
+ If this call is invoked, all previously added matches since the
+ last invocation of
+ <function>sd_journal_add_disjunction()</function> or
+ <function>sd_journal_add_conjunction()</function> are combined in
+ an OR with all matches added afterwards, until
+ <function>sd_journal_add_disjunction()</function> or
+ <function>sd_journal_add_conjunction()</function> is invoked again
+ to begin the next OR or AND term. </para>
+
+ <para><function>sd_journal_add_conjunction()</function> may be
+ used to insert a conjunction (i.e. logical AND) in the match list.
+ If this call is invoked, all previously added matches since the
+ last invocation of
+ <function>sd_journal_add_conjunction()</function> are combined in
+ an AND with all matches added afterwards, until
+ <function>sd_journal_add_conjunction()</function> is invoked again
+ to begin the next AND term. The combination of
+ <function>sd_journal_add_match()</function>,
+ <function>sd_journal_add_disjunction()</function> and
+ <function>sd_journal_add_conjunction()</function> may be used to
+ build complex search terms, even though full logical expressions
+ are not available. Note that
+ <function>sd_journal_add_conjunction()</function> operates one
+ level 'higher' than
+ <function>sd_journal_add_disjunction()</function>. It is hence
+ possible to build an expression of AND terms, consisting of OR
+ terms, consisting of AND terms, consisting of OR terms of matches
+ (the latter OR expression is implicitly created for matches with
+ the same field name, see above).</para>
+
+ <para><function>sd_journal_flush_matches()</function> may be used
+ to flush all matches, disjunction and conjunction terms again.
+ After this call all filtering is removed and all entries in the
+ journal will be iterated again.</para>
+
+ <para>Note that filtering via matches only applies to the way the
+ journal is read, it has no effect on storage on disk.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para><function>sd_journal_add_match()</function>,
+ <function>sd_journal_add_disjunction()</function> and
+ <function>sd_journal_add_conjunction()</function>
+ return 0 on success or a negative errno-style error
+ code. <function>sd_journal_flush_matches()</function>
+ returns nothing.</para>
+ </refsect1>
+
+ <xi:include href="libsystemd-pkgconfig.xml" />
+
+ <refsect1>
+ <title>Examples</title>
+
+ <para>The following example adds matches to a journal context
+ object to iterate only through messages generated by the Avahi
+ service at the four error log levels, plus all messages of the
+ message ID 03bb1dab98ab4ecfbf6fff2738bdd964 coming from any
+ service (this example lacks the necessary error checking):</para>
+
+ <programlisting>…
+int add_matches(sd_journal *j) {
+ sd_journal_add_match(j, "_SYSTEMD_UNIT=avahi-daemon.service", 0);
+ sd_journal_add_match(j, "PRIORITY=0", 0);
+ sd_journal_add_match(j, "PRIORITY=1", 0);
+ sd_journal_add_match(j, "PRIORITY=2", 0);
+ sd_journal_add_match(j, "PRIORITY=3", 0);
+ sd_journal_add_disjunction(j);
+ sd_journal_add_match(j, "MESSAGE_ID=03bb1dab98ab4ecfbf6fff2738bdd964", 0);
+}</programlisting>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>