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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">
<!--
SPDX-License-Identifier: LGPL-2.1+
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>.
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>
<refsect1>
<title>Notes</title>
<para>All functions listed here are thread-agnostic and only a single thread may operate
on a given <structname>sd_journal</structname> object.</para>
<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 a shared library, which can
be compiled and linked to with the
<constant>libsystemd</constant> <citerefentry project='die-net'><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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