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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2012 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_journal_add_match">
<refentryinfo>
<title>sd_journal_add_match</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</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 <systemd/sd-journal.h></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>. Matches
are of the form <literal>FIELD=value</literal>, where
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
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>
<refsect1>
<title>Notes</title>
<para>The <function>sd_journal_add_match()</function>,
<function>sd_journal_add_disjunction()</function>,
<function>sd_journal_add_conjunction()</function> and
<function>sd_journal_flush_matches()</function>
interfaces are available as shared library, which can
be compiled and linked to with the
<constant>libsystemd-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<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>
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