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<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 &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>. 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 a 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>