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  <a href="../libudev/index.html">gudev </a><span style="float:right">systemd 215</span><hr><div class="refentry"><a name="sd_journal_add_match"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_journal_add_match, sd_journal_add_disjunction, sd_journal_add_conjunction, sd_journal_flush_matches — Add or remove entry matches</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;systemd/sd-journal.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_add_match</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const void *<var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_add_disjunction</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_add_conjunction</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <b class="fsfunc">sd_journal_flush_matches</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm214175498320"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description"></a></h2><p><code class="function">sd_journal_add_match()</code> adds
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                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
                <a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>
                and
                <a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a>. Matches
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                are of the form "<code class="literal">FIELD=value</code>", where
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                the field 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 value
                part may be any value, including binary. If a match is
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                applied, only entries with this field set will be
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                iterated. Multiple matches may be active at the same
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                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
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                field takes one of the specified values will be
                iterated. Well known fields are documented in
                <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>. Whenever
                a new match is added the current entry position is
                reset, and
                <a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a> (or a similar call)
                needs to be called before entries can be read
                again.</p><p><code class="function">sd_journal_add_disjunction()</code>
                may be used to insert a disjunction (i.e. logical OR)
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                in the match list. If this call is invoked, all
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                previously added matches since the last invocation of
                <code class="function">sd_journal_add_disjunction()</code> or
                <code class="function">sd_journal_add_conjunction()</code> are
                combined in an OR with all matches added afterwards,
                until
                <code class="function">sd_journal_add_disjunction()</code> or
                <code class="function">sd_journal_add_conjunction()</code> is
                invoked again to begin the next OR or AND
                term. </p><p><code class="function">sd_journal_add_conjunction()</code>
                may be used to insert a conjunction (i.e. logical AND)
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                in the match list. If this call is invoked, all
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                previously added matches since the last invocation of
                <code class="function">sd_journal_add_conjunction()</code> are
                combined in an AND with all matches added afterwards,
                until
                <code class="function">sd_journal_add_conjunction()</code> is
                invoked again to begin the next AND term. The
                combination of
                <code class="function">sd_journal_add_match()</code>,
                <code class="function">sd_journal_add_disjunction()</code> and
                <code class="function">sd_journal_add_conjunction()</code> may
                be used to build complex search terms, even though
                full logical expressions are not available. Note that
                <code class="function">sd_journal_add_conjunction()</code>
                operates one level 'higher' than
                <code class="function">sd_journal_add_disjunction()</code>. 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).</p><p><code class="function">sd_journal_flush_matches()</code>
                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.</p><p>Note that filtering via matches only applies to
                the way the journal is read, it has no effect on storage
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                on disk.</p></div><div class="refsect1"><a name="idm214175672320"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value"></a></h2><p><code class="function">sd_journal_add_match()</code>,
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                <code class="function">sd_journal_add_disjunction()</code> and
                <code class="function">sd_journal_add_conjunction()</code>
                return 0 on success or a negative errno-style error
                code. <code class="function">sd_journal_flush_matches()</code>
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                returns nothing.</p></div><div class="refsect1"><a name="idm214175668288"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes"></a></h2><p>The <code class="function">sd_journal_add_match()</code>,
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                <code class="function">sd_journal_add_disjunction()</code>,
                <code class="function">sd_journal_add_conjunction()</code> and
                <code class="function">sd_journal_flush_matches()</code>
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                interfaces are available as a shared library, which can
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                be compiled and linked to with the
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                <code class="constant">libsystemd</code> <a href="pkg-config.html"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
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                file.</p></div><div class="refsect1"><a name="idm214175662688"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples"></a></h2><p>The following example adds matches to a journal
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                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):</p><pre class="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);
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}</pre></div><div class="refsect1"><a name="idm214175659984"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also"></a></h2><p>
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                        <a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
                        <a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>,
                        <a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>,
                        <a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>,
                        <a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a>,
                        <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>
                </p></div></div></body></html>