240 lines
6.2 KiB
Plaintext
240 lines
6.2 KiB
Plaintext
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_trigger.sgml,v 1.12 2000/10/05 19:48:18 momjian Exp $
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Postgres documentation
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-->
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<refentry id="SQL-CREATETRIGGER">
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<refmeta>
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<refentrytitle id="SQL-CREATETRIGGER-TITLE">
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CREATE TRIGGER
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</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>
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CREATE TRIGGER
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</refname>
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<refpurpose>
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Creates a new trigger
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</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<refsynopsisdivinfo>
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<date>2000-03-25</date>
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</refsynopsisdivinfo>
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<synopsis>
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CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTER } { <replaceable class="PARAMETER">event</replaceable> [OR ...] }
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ON <replaceable class="PARAMETER">table</replaceable> FOR EACH { ROW | STATEMENT }
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EXECUTE PROCEDURE <replaceable class="PARAMETER">func</replaceable> ( <replaceable class="PARAMETER">arguments</replaceable> )
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</synopsis>
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<refsect2 id="R2-SQL-CREATETRIGGER-1">
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<refsect2info>
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<date>1998-09-21</date>
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</refsect2info>
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<title>
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Inputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><replaceable class="parameter">name</replaceable></term>
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<listitem>
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<para>
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The name of an existing trigger.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">table</replaceable></term>
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<listitem>
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<para>
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The name of a table.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">event</replaceable></term>
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<listitem>
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<para>
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One of INSERT, DELETE or UPDATE.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">func</replaceable></term>
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<listitem>
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<para>
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A user-supplied function.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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<refsect2 id="R2-SQL-CREATETRIGGER-2">
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<refsect2info>
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<date>1998-09-21</date>
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</refsect2info>
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<title>
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Outputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><computeroutput>
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CREATE
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</computeroutput></term>
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<listitem>
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<para>
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This message is returned if the trigger is successfully created.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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</refsynopsisdiv>
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<refsect1 id="R1-SQL-CREATETRIGGER-1">
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<refsect1info>
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<date>1998-09-21</date>
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</refsect1info>
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<title>
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Description
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</title>
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<para>
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<command>CREATE TRIGGER</command> will enter a new trigger into the current
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data base. The trigger will be associated with the relation
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<replaceable class="parameter">table</replaceable> and will execute
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the specified function <replaceable class="parameter">func</replaceable>.
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</para>
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<para>
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The trigger can be specified to fire either before BEFORE the
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operation is attempted on a tuple (before constraints
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are checked and the <command>INSERT</command>, <command>UPDATE</command> or
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<command>DELETE</command> is attempted) or
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AFTER the operation has been attempted (e.g., after constraints
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are checked and the <command>INSERT</command>,
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<command>UPDATE</command> or <command>DELETE</command> has
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completed). If the
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trigger fires before the event, the trigger may
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skip the operation for the current tuple, or change the tuple
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being inserted (for <command>INSERT</command> and
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<command>UPDATE</command> operations only). If
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the trigger fires after the event, all changes, including the
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last insertion, update, or deletion, are "visible" to the trigger.
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</para>
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<para>
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Refer to the chapters on SPI and Triggers in the
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<citetitle>PostgreSQL Programmer's Guide</citetitle> for more
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information.
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</para>
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<refsect2 id="R2-SQL-CREATETRIGGER-3">
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<refsect2info>
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<date>1998-09-21</date>
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</refsect2info>
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<title>
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Notes
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</title>
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<para>
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<command>CREATE TRIGGER</command> is a <productname>Postgres</productname>
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language extension.
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</para>
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<para>
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Only the relation owner may create a trigger on this relation.
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</para>
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<para>
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As of the current release (v7.0), STATEMENT triggers are not implemented.
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</para>
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<para>
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Refer to <command>DROP TRIGGER</command> for information on how to
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remove triggers.
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</para>
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</refsect2>
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</refsect1>
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<refsect1 id="R1-SQL-CREATETRIGGER-2">
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<title>
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Usage
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</title>
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<para>
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Check if the specified distributor code exists in the distributors
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table before appending or updating a row in the table films:
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<programlisting>
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CREATE TRIGGER if_dist_exists
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BEFORE INSERT OR UPDATE ON films FOR EACH ROW
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EXECUTE PROCEDURE check_primary_key ('did', 'distributors', 'did');
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</programlisting>
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</para>
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<para>
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Before cancelling a distributor or updating its code, remove every
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reference to the table films:
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<programlisting>
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CREATE TRIGGER if_film_exists
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BEFORE DELETE OR UPDATE ON distributors FOR EACH ROW
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EXECUTE PROCEDURE check_foreign_key (1, 'CASCADE', 'did', 'films', 'did');
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</programlisting>
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</para>
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</refsect1>
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<refsect1 id="R1-SQL-CREATETRIGGER-3">
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<title>
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Compatibility
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</title>
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<refsect2 id="R2-SQL-CREATETRIGGER-4">
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<refsect2info>
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<date>1998-09-21</date>
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</refsect2info>
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<title>
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SQL92
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</title>
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<para>
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There is no <command>CREATE TRIGGER</command> in <acronym>SQL92</acronym>.
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</para>
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<para>
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The second example above may also be done by using a FOREIGN KEY
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constraint as in:
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<programlisting>
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CREATE TABLE distributors (
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did DECIMAL(3),
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name VARCHAR(40),
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CONSTRAINT if_film_exists
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FOREIGN KEY(did) REFERENCES films
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ON UPDATE CASCADE ON DELETE CASCADE
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);
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</programlisting>
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</para>
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</refsect2>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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sgml-local-catalogs:"/usr/lib/sgml/catalog"
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End:
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