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$Header: /cvsroot/pgsql/doc/src/sgml/ref/psql-ref.sgml,v 1.52 2001/05/12 19:44:45 petere Exp $
Postgres documentation
-->

<refentry id="APP-PSQL">
 <docinfo>
  <date>2000-12-25</date>
 </docinfo>

  <refmeta>
    <refentrytitle id="app-psql-title"><application>psql</application></refentrytitle>
    <manvolnum>1</manvolnum>
    <refmiscinfo>Application</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname><application>psql</application></refname>
    <refpurpose>
      <productname>Postgres</productname> interactive terminal
    </refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <refsynopsisdivinfo>
      <date>1999-10-26</date>
    </refsynopsisdivinfo>

    <synopsis>psql [ <replaceable class="parameter">options</replaceable> ] [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">user</replaceable> ] ]</synopsis>

  <refsect2 id="R2-APP-PSQL-1">
    <refsect2info>
      <date>1998-09-26</date>
    </refsect2info>

    <title>Summary</title>

    <para>
     <application>psql</application> is a terminal-based front-end to 
     <productname>Postgres</productname>. It enables you to type in queries
     interactively, issue them to <productname>Postgres</productname>, and see
     the query results. Alternatively, input can be from a file.
     In addition, it provides a number of meta-commands and
     various shell-like features to facilitate writing scripts and automating a wide
     variety of tasks.
    </para>

  </refsect2>

</refsynopsisdiv>

<refsect1 id="R1-APP-PSQL-1">
  <refsect1info>
    <date>1998-10-26</date>
  </refsect1info>

  <title>Description</title>

  <refsect2 id="R2-APP-PSQL-connecting">
    <refsect2info>
      <date>2000-01-14</date>
    </refsect2info>
   
    <title>Connecting To A Database</title>

    <para>
    <application>psql</application> is a regular <productname>Postgres</productname>
    client application. In order to connect to a database you need to know the
    name of your target database, the hostname and port number of the server
    and what user name you want to connect as. <application>psql</application> can be
    told about those parameters via command line options, namely <option>-d</option>,
    <option>-h</option>, <option>-p</option>, and <option>-U</option> respectively.
    If an argument is found that does not belong to any option it will be interpreted
    as the database name (or the user name, if the database name is also
	 given). Not all these options are required, defaults do apply.
    If you omit the host name psql will connect via a Unix domain socket
    to a server on the
    local host. The default port number is compile-time determined. Since the database
    server uses the same default, you will not have to specify the port in most
    cases. The default user name is your Unix username, as is the default
    database name.
    Note that you can't just connect to any database under any username. Your database
    administrator should have informed you about your access rights. To save you some typing
    you can also set the environment variables <envar>PGDATABASE</envar>,
    <envar>PGHOST</envar>, <envar>PGPORT</envar> and <envar>PGUSER</envar>
    to appropriate values.
    </para>

    <para>
    If the connection could not be made for any reason (e.g., insufficient
    privileges, postmaster is not running on the server, etc.),
    <application>psql</application> will return an error and terminate.
    </para>
  </refsect2>

  <refsect2 id="R2-APP-PSQL-4">
    <refsect2info>
      <date>1998-09-26</date>
    </refsect2info>

    <title>Entering Queries</title>

    <para>
    In normal operation, <application>psql</application> provides a prompt with
    the name of the database to which <application>psql</application> is currently
    connected, followed by the string "=>". For example,
<programlisting>
$ <userinput>psql testdb</userinput>
Welcome to psql, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help on internal slash commands
       \g or terminate with semicolon to execute query
       \q to quit

testdb=>
</programlisting>
    </para>

    <para>
    At the prompt, the user may type in <acronym>SQL</acronym> queries.  
    Ordinarily, input lines are sent to the backend when a query-terminating
    semicolon is reached. An end of line does not terminate a query! Thus queries
    can be spread over several lines for clarity. If the query was sent and without
    error, the query results are displayed on the screen.
    </para>

    <para>
    Whenever a query is executed, <application>psql</application> also polls
    for asynchronous notification events generated by
    <xref linkend="SQL-LISTEN" endterm="SQL-LISTEN-title"> and
    <xref linkend="SQL-NOTIFY" endterm="SQL-NOTIFY-title">.
    </para>
  </refsect2>
</refsect1>

<refsect1 id="R1-APP-PSQL-2">
    <refsect1info>
      <date>1998-09-26</date>
    </refsect1info>

    <title><application>psql</application> Meta-Commands</title>

    <para>
    Anything you enter in <application>psql</application> that begins with an
    unquoted backslash is a <application>psql</application> meta-command that is
    processed by <application>psql</application> itself.
    These commands are what makes
    <application>psql</application> interesting for administration or scripting.
    Meta-commands are more commonly called slash or backslash commands.
    </para>

    <para>
    The format of a <application>psql</application> command is the backslash, 
    followed immediately by a command verb, then any arguments. The arguments
    are separated from the command verb and each other by any number of 
    whitespace characters.
    </para>

    <para>
    To include whitespace into an argument you must quote it with a single
    quote. To include a single quote into such an argument, precede it by
    a backslash. Anything contained in single quotes is furthermore subject to
    C-like substitutions for <literal>\n</literal> (new line), <literal>\t</literal>
     (tab), <literal>\</literal><replaceable>digits</replaceable>,
    <literal>\0</literal><replaceable>digits</replaceable>, and
    <literal>\0x</literal><replaceable>digits</replaceable>
    (the character with the given decimal, octal, or hexadecimal code).
    </para>

    <para>
    If an unquoted argument begins with a colon (<literal>:</literal>),
    it is taken as a variable and the value of the variable is taken as the
    argument instead.
    </para>

    <para>
    Arguments that are quoted in <quote>backticks</quote> (<literal>`</literal>)
    are taken as a command line that is passed to the shell. The output of the
    command (with a trailing newline removed) is taken as the argument value.
    The above escape sequences also apply in backticks.
    </para>

    <para>
    Some commands take the name of an <acronym>SQL</acronym> identifier (such as
    a table name) as argument. These arguments follow the syntax rules of
    <acronym>SQL</acronym> regarding double quotes: an identifier without
    double quotes is coerced to lower-case. For all other commands
    double quotes are not special and will become part of the argument.
    </para>

    <para>
    Parsing for arguments stops when another unquoted backslash occurs. This
    is taken as the beginning of a new meta-command. The special sequence
    <literal>\\</literal>
    (two backslashes) marks the end of arguments and continues parsing
    <acronym>SQL</acronym> queries, if any. That way <acronym>SQL</acronym> and
    <application>psql</application> commands can be freely mixed on a line.
    But in any case, the arguments of a meta-command cannot continue beyond the end
    of the line. 
    </para>

    <para>
    The following meta-commands are defined:

    <variablelist>
      <varlistentry>
        <term><literal>\a</literal></term>
        <listitem>
        <para>
	If the current table output format is unaligned, switch to aligned.
	If it is not unaligned, set it to unaligned. This command is
	kept for backwards compatibility. See <command>\pset</command> for a
	general solution.
        </para>
        </listitem>
      </varlistentry>

      <varlistentry>
       <term><literal>\cd</literal> <optional><replaceable>directory</replaceable></optional></term>
       <listitem>
        <para>
	 Change the current working directory to
	 <replaceable>directory</replaceable>.  Without argument,
	 change to the current user's home directory.
        </para>

	<tip>
	 <para>
	  To print your current working directory, use <literal>\!pwd</literal>.
	 </para>
	</tip>
       </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\C</literal> [ <replaceable class="parameter">title</replaceable> ]</term>
        <listitem>
        <para>
        Set the title of any tables being printed as the result of a query or
        unset any such title. This command is equivalent to
        <literal>\pset title <replaceable class="parameter">title</replaceable></literal>.
        (The name of this
        command derives from <quote>caption</quote>, as it was previously only
	used to set the caption in an <acronym>HTML</acronym> table.)
        </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\connect</literal> (or <literal>\c</literal>) [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] ]</term>
        <listitem>
        <para>
	Establishes a connection to a new database and/or under a user name. The
	previous connection is closed.
	If <replaceable class="parameter">dbname</replaceable> is <literal>-</literal>
	the current database name is assumed.
	</para>

	<para>
	If <replaceable class="parameter">username</replaceable> is omitted
        the current user name is assumed.
	</para>

	<para>
	As a special rule, <command>\connect</command> without any arguments will connect
	to the default database as the default user (as you would have gotten
	by starting <application>psql</application> without any arguments).
	</para>

	<para>
	If the connection attempt failed (wrong username, access denied, etc.), the
	previous connection will be kept if and only if <application>psql</application> is
	in interactive mode. When executing a non-interactive script, processing
	will immediately stop with an error. This distinction was chosen as a user
	convenience against typos on the one hand, and a safety mechanism that
	scripts are not accidentally acting on the wrong database on the other hand.
	</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\copy</literal> <replaceable class="parameter">table</replaceable>
        [ <literal>with oids</literal> ] { <literal>from</literal> | <literal>to</literal> }
	<replaceable class="parameter">filename</replaceable> | stdin | stdout
        [ <literal>using delimiters</literal> '<replaceable class="parameter">characters</replaceable>' ]
        [ <literal>with null as</literal> '<replaceable class="parameter">string</replaceable>' ]
        </term>

        <listitem>
        <para>
        Performs a frontend (client) copy. This is an operation that runs an
	<acronym>SQL</acronym> <xref linkend="SQL-COPY" endterm="SQL-COPY-title"> command,
        but instead of the backend's reading or writing the specified file, and 
        consequently requiring backend access and special user privilege, 
	as well as being bound to the file system accessible by the backend,
        <application>psql</application> reads or writes the 
        file and routes the data between the backend and the local file system.
	</para>

	<para>
	The syntax of the command is similar to that of the <acronym>SQL</acronym>
	<command>COPY</command> command (see its description for the details).
	Note that, because of this, special parsing rules apply to the
	<command>\copy</command> command. In particular, the variable
	substitution rules and backslash escapes do not apply.
	</para>

        <tip>
        <para>
	This operation is not as efficient as the <acronym>SQL</acronym> 
	<command>COPY</command> command because all data must pass through the
	client/server IP or socket connection. For large amounts of data the other
	technique may be preferable.
        </para>
        </tip>

        <note>
        <para>
        Note the difference in interpretation of <literal>stdin</literal> and <literal>stdout</literal>
        between frontend and backend copies: in a frontend copy these always refer
        to <application>psql</application>'s input and output stream. On a backend
        copy <literal>stdin</literal> comes from wherever the <command>COPY</command>
        itself came from (for example, a script run with the <option>-f</option> option),
        and <literal>stdout</literal> refers to the query output stream (see
        <command>\o</command> meta-command below).
        </para>
        </note>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\copyright</literal></term>
        <listitem>
        <para>
        Shows the copyright and distribution terms of <application>Postgres</application>.
        </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\d</literal> <replaceable class="parameter">relation</replaceable> </term>

        <listitem>
        <para>
	Shows all columns of <replaceable class="parameter">relation</replaceable>
	(which could be a table, view, index, or sequence),
	their types, and any special attributes such as <literal>NOT NULL</literal>
	or defaults, if any.
	If the relation is, in fact, a table, any defined indices are also listed.
	If the relation is a view, the view definition is also shown.
	</para>

	<para>
	The command form <literal>\d+</literal> is identical, but any comments
        associated with the table columns are shown as well.
	</para>

	<note>
	<para>
	If <command>\d</command> is called without any arguments, it is
	equivalent to <command>\dtvs</command> which will show a list
	of all tables, views, and sequences. This is purely a convenience
	measure.
	</para>
	</note>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\da</literal> [ <replaceable class="parameter">pattern</replaceable> ]</term>

        <listitem>
        <para>
        Lists all available aggregate functions, together with the data type they operate on.
	If <replaceable class="parameter">pattern</replaceable>
	(a regular expression) is specified, only matching aggregates are shown.
        </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\dd</literal> [ <replaceable class="parameter">object</replaceable> ]</term>
        <listitem>
        <para>
        Shows the descriptions of <replaceable class="parameter">object</replaceable>
        (which can be a regular expression), or of all objects if no argument is given.
        (<quote>Object</quote> covers aggregates, functions, operators, types, relations
        (tables, views, indices, sequences, large objects), rules, and triggers.) For example:
<programlisting>
=> <userinput>\dd version</userinput>
              Object descriptions
  Name   |   What   |        Description
---------+----------+---------------------------
 version | function | PostgreSQL version string
(1 row)
</programlisting>
        </para>

        <para>
        Descriptions for objects can be generated with the <command>COMMENT ON</command>
        <acronym>SQL</acronym> command.
	</para>

        <note>
        <para>
        <productname>Postgres</productname> stores the object descriptions in the
        pg_description system table.
        </para>
        </note>

        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\df [ <replaceable class="parameter">pattern</replaceable> ]</literal></term>

        <listitem>
        <para>
        Lists available functions, together with their argument and return types.
        If <replaceable class="parameter">pattern</replaceable>
        (a regular expression) is specified, only matching functions are shown.
        If the form <literal>\df+</literal> is used, additional information about
        each function, including language and description, is shown.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\distvS [ <replaceable class="parameter">pattern</replaceable> ]</literal></term>

	<listitem>
	<para>
	This is not the actual command name: The letters i, s, t, v, S stand for
	index, sequence, table, view, and system table, respectively. You can specify
	any or all of them in any order to obtain a listing of them, together with
	who the owner is.
	</para>

	<para>
	If <replaceable class="parameter">pattern</replaceable> is specified,
	it is a regular expression that restricts the listing to those objects
	whose name matches. If one appends a <quote>+</quote> to the command name,
	each object is listed with its associated description, if any.
	</para>
	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\dl</literal></term>
	<listitem>
	<para>
	This is an alias for <command>\lo_list</command>, which shows a list of large objects.
	</para>
	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\do [ <replaceable class="parameter">name</replaceable> ]</literal></term>
        <listitem>
        <para>
        Lists available operators with their operand and return types.
        If <replaceable class="parameter">name</replaceable>
        is specified, only operators with that name will be shown.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\dp</literal> [ <replaceable class="parameter">pattern</replaceable> ]</term>
	<listitem>
	<para>
	This is an alias for <command>\z</command> which was included for its
	greater mnemonic value (<quote>display permissions</quote>).
	</para>
	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\dT [ <replaceable class="parameter">pattern</replaceable> ]</literal></term>
        <listitem>
        <para>
        Lists all data types or only those that match <replaceable class="parameter">pattern</replaceable>.
        The command form <literal>\dT+</literal> shows extra information.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\du [ <replaceable class="parameter">pattern</replaceable> ]</literal></term>
        <listitem>
        <para>
        Lists all configured users or only those that match <replaceable class="parameter">pattern</replaceable>.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\edit</literal> (or <literal>\e</literal>) [ <replaceable class="parameter">filename</replaceable> ]</term>

        <listitem>
        <para>
        If <replaceable class="parameter">filename</replaceable> is specified,
        the file is edited; after the editor exits, its content is copied
        back to the query buffer. If no argument is given, the current query
        buffer is copied to a temporary file which is then edited in the same
        fashion.
        </para>

        <para>
        The new query buffer is then re-parsed according to the normal rules of
        <application>psql</application>, where the whole buffer is treated as
        a single line. (Thus you cannot make scripts this way.
        Use <command>\i</command> for that.) This means also that
        if the query ends with (or rather contains) a semicolon, it is immediately
        executed. In other cases it will merely wait in the query buffer.
        </para>

        <tip>
        <para>
        <application>psql</application> searches the environment variables
        <envar>PSQL_EDITOR</envar>, <envar>EDITOR</envar>, and <envar>VISUAL</envar>
        (in that order) for an editor to use. If all of them are unset,
        <filename>/bin/vi</filename> is run.
        </para>
        </tip>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\echo</literal> <replaceable class="parameter">text</replaceable> [ ... ]</term>
        <listitem>
	<para>
        Prints the arguments to the standard output, separated by one space and
        followed by a newline. This can be useful to
        intersperse information in the output of scripts. For example:
<programlisting>
=> <userinput>\echo `date`</userinput>
Tue Oct 26 21:40:57 CEST 1999
</programlisting>
        If the first argument is an unquoted <literal>-n</literal> the the trailing
        newline is not written.
	</para>

	<tip>
	<para>
	If you use the <command>\o</command> command to redirect your query output
	you may wish to use <command>\qecho</command> instead of this command.
	</para>
	</tip>
	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\encoding</literal> [ <replaceable class="parameter">encoding</replaceable> ]</term>

        <listitem>
        <para>
        Sets the client encoding, if you are using multibyte encodings.
        Without an argument, this command shows the current encoding.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\f</literal> [ <replaceable class="parameter">string</replaceable> ]</term>

        <listitem>
        <para>
        Sets the field separator for unaligned query output. The default is
pipe (<literal>|</literal>). See also <command>\pset</command> for a generic way
	of setting output options.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\g</literal> [ { <replaceable class="parameter">filename</replaceable> | <literal>|</literal><replaceable class="parameter">command</replaceable> } ]</term>

        <listitem>
        <para>
        Sends the current query input buffer to the backend and optionally
        saves the output in <replaceable class="parameter">filename</replaceable>
        or pipes the output into a separate Unix shell to execute
        <replaceable class="parameter">command</replaceable>. A bare <literal>\g</literal>
	is virtually equivalent to a semicolon. A <literal>\g</literal> with argument
	is a <quote>one-shot</quote> alternative to the <command>\o</command> command.
        </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\help</literal> (or <literal>\h</literal>) [ <replaceable class="parameter">command</replaceable> ]</term>
        <listitem>
        <para>
        Give syntax help on the specified <acronym>SQL</acronym> command.  
        If <replaceable class="parameter">command</replaceable> is not specified,
        then <application>psql</application> will 
        list all the commands for which syntax help is
        available.  If <replaceable class="parameter">command</replaceable>
        is an asterisk (<quote>*</quote>), then
        syntax help on all <acronym>SQL</acronym> commands is shown.
        </para>

	<note>
	<para>
	To simplify typing, commands that consists of several words do not have to be quoted.
	Thus it is fine to type <userinput>\help alter table</userinput>.
	</para>
	</note>	
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\H</literal></term>
        <listitem>
        <para>
	Turns on <acronym>HTML</acronym> query output format. If the <acronym>HTML</acronym>
	format is already on, it is switched back to the default aligned text format. This
	command is for compatibility and convenience, but see <command>\pset</command> about
	setting other output options.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\i</literal> <replaceable class="parameter">filename</replaceable></term>
        <listitem>
        <para>
        Reads input from the file <replaceable class="parameter">filename</replaceable>
	and executes it as though it had been typed on the keyboard.
        </para>
	<note>
	<para>
	If you want to see the lines on the screen as they are read you must set
	the variable <envar>ECHO</envar> to <literal>all</literal>.
	</para>
	</note>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\l</literal> (or <literal>\list</literal>)</term>
        <listitem>
        <para>
        List all the databases in the server as well as their owners. Append a
        <quote>+</quote> to the command name to see any descriptions
        for the databases as well. If your <productname>Postgres</productname>
	installation was
	compiled with multibyte encoding support, the encoding scheme of each
	database is shown as well.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\lo_export</literal> <replaceable class="parameter">loid</replaceable> <replaceable class="parameter">filename</replaceable></term>

	<listitem>
	<para>
	Reads the large object with <acronym>OID</acronym> <replaceable class="parameter">loid</replaceable>
	from the database and writes it to <replaceable class="parameter">filename</replaceable>.
	Note that this is subtly different from the server function <function>lo_export</function>,
	which acts with the permissions of the user that the database server runs as and
	on the server's file system.
	</para>
	<tip>
	<para>
	Use <command>\lo_list</command> to find out the large object's <acronym>OID</acronym>.
	</para>
	</tip>
	<note>
	<para>
	See the description of the <envar>LO_TRANSACTION</envar> variable for
	important information concerning all large object operations.
	</para>
	</note>
	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\lo_import</literal> <replaceable class="parameter">filename</replaceable> [ <replaceable class="parameter">comment</replaceable> ]</term>

	<listitem>
	<para>
	Stores the file into a <productname>Postgres</productname> <quote>large object</quote>.
	Optionally, it associates the given comment with the object. Example:
<programlisting>
foo=> <userinput>\lo_import '/home/peter/pictures/photo.xcf' 'a picture of me'</userinput>
lo_import 152801
</programlisting>
	The response indicates that the large object received object id 152801
	which one ought to remember if one wants to access the object ever again.
	For that reason it is recommended to always associate a human-readable
	comment with every object. Those can then be seen with the
	<command>\lo_list</command> command.
	</para>

	<para>
	Note that this command is subtly different from the server-side <function>lo_import</function>
	because it acts as the local user on the local file system, rather than the server's
	user and file system.
	</para>

	<note>
	<para>
	See the description of the <envar>LO_TRANSACTION</envar> variable for
	important information concerning all large object operations.
	</para>
	</note>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\lo_list</literal></term>
	<listitem>
	<para>
	Shows a list of all <productname>Postgres</productname> <quote>large
	objects</quote> currently stored in the database, along with any
	comments provided for them.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>\lo_unlink</literal> <replaceable class="parameter">loid</replaceable></term>

	<listitem>
	<para>
	Deletes the large object with <acronym>OID</acronym> <replaceable class="parameter">loid</replaceable>
	from the database.
	</para>

	<tip>
	<para>
	Use <command>\lo_list</command> to find out the large object's <acronym>OID</acronym>.
	</para>
	</tip>
	<note>
	<para>
	See the description of the <envar>LO_TRANSACTION</envar> variable for
	important information concerning all large object operations.
	</para>
	</note>
	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\o</literal> [ {<replaceable class="parameter">filename</replaceable> | <literal>|</literal><replaceable class="parameter">command</replaceable>} ]</term>

        <listitem>
        <para>
        Saves future query results to the file
	<replaceable class="parameter">filename</replaceable> or pipes future
        results into a separate Unix shell to execute
	<replaceable class="parameter">command</replaceable>.
        If no arguments are specified, the query output will be reset to
        <filename>stdout</filename>.
        </para>

	<para>
	<quote>Query results</quote> includes all tables, command responses,
        and notices obtained
	from the database server, as well as output of various backslash
	commands that query the database (such as <command>\d</command>),
        but not error messages.
	</para>

	<tip>
	<para>
	To intersperse text output in between query results, use <command>\qecho</command>.
	</para>
	</tip>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\p</literal></term>
        <listitem>
        <para>
        Print the current query buffer to the standard output.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\pset</literal> <replaceable class="parameter">parameter</replaceable> [ <replaceable class="parameter">value</replaceable> ]</term>

	<listitem>
	<para>
	This command sets options affecting the output of query result tables.
	<replaceable class="parameter">parameter</replaceable> describes which option
	is to be set. The semantics of <replaceable class="parameter">value</replaceable>
	depend thereon.
	</para>

	<para>
	Adjustable printing options are:
	<variablelist>
	  <varlistentry>
	  <term><literal>format</literal></term>
	  <listitem>
	  <para>
	  Sets the output format to one of <literal>unaligned</literal>,
	  <literal>aligned</literal>, <literal>html</literal>, or <literal>latex</literal>.
	  Unique abbreviations are allowed. (That would mean one letter is enough.)
	  </para>

	  <para>
	  <quote>Unaligned</quote> writes all fields of a tuple on a line, separated
	  by the currently active field separator. This is intended to create output
	  that might be intended to be read in by other programs (tab-separated,
	  comma-separated).
	  <quote>Aligned</quote> mode is the
	  standard, human-readable, nicely formatted text output that is default.
	  The <quote><acronym>HTML</acronym></quote> and <quote>LaTeX</quote> modes
	  put out tables that are intended to be included in documents using the
	  respective mark-up language. They are not complete documents! (This might
	  not be so dramatic in <acronym>HTML</acronym>, but in LaTeX you must
	  have a complete document wrapper.)
	  </para>
	  </listitem>
          </varlistentry>

	  <varlistentry>
	  <term><literal>border</literal></term>
	  <listitem>
	  <para>
	  The second argument must be a number. In general, the higher the number
	  the more borders and lines the tables will have, but this depends on
	  the particular format. In <acronym>HTML</acronym> mode, this will
	  translate directly into the <literal>border=...</literal> attribute, in
	  the others only values 0 (no border), 1 (internal dividing lines), and 2
	  (table frame) make sense.
	  </para>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>expanded</literal> (or <literal>x</literal>)</term>
	  <listitem>
	  <para>
	  Toggles between regular and expanded format. When expanded format is
	  enabled, all output has two columns with the field name on the left
	  and the data on the right. This mode is useful if the data wouldn't
	  fit on the screen in the normal <quote>horizontal</quote> mode.
	  </para>

	  <para>
	  Expanded mode is supported by all four output modes.
	  </para>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>null</literal></term>
	  <listitem>
	  <para>
	  The second argument is a string that should be printed whenever a field
	  is null. The default is not to print anything, which can easily be mistaken
	  for, say, an empty string. Thus, one might choose to write
	  <literal>\pset null '(null)'</literal>.
	  </para>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>fieldsep</literal></term>
	  <listitem>
	  <para>
	  Specifies the field separator to be used in unaligned output mode. That way
	  one can create, for example, tab- or comma-separated output, which other
	  programs might prefer. To set a tab as field separator, type
	  <literal>\pset fieldsep '\t'</literal>. The default field separator is
	  <literal>'|'</literal> (a <quote>pipe</quote> symbol).
	  </para>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>footer</literal></term>
	  <listitem>
	  <para>
	  Toggles the display of the default footer <literal>(x rows)</literal>.
	  </para>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>recordsep</literal></term>
	  <listitem>
	  <para>
          Specifies the record (line) separator to use in unaligned output mode. The default
          is a newline character.
	  </para>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>tuples_only</literal> (or <literal>t</literal>)</term>
	  <listitem>
	  <para>
	  Toggles between tuples only and full display. Full display may show
	  extra information such as column headers, titles, and various footers.
	  In tuples only mode, only actual table data is shown.
	  </para>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>title</literal> [ <replaceable class="parameter">text</replaceable> ]</term>
	  <listitem>
	  <para>
	  Sets the table title for any subsequently printed tables. This can be
	  used to give your output descriptive tags. If no argument is given,
	  the title is unset.
	  </para>

	  <note>
	  <para>
	  This formerly only affected <acronym>HTML</acronym> mode. You can now
	  set titles in any output format.
	  </para>
	  </note>
	  </listitem>
	  </varlistentry>

	  <varlistentry>
	  <term><literal>tableattr</literal> (or <literal>T</literal>) [ <replaceable class="parameter">text</replaceable> ]</term>
	  <listitem>
	  <para>
	  Allows you to specify any attributes to be placed inside the <acronym>HTML</acronym>
	  <sgmltag>table</sgmltag> tag. This could for example be
	  <literal>cellpadding</literal> or <literal>bgcolor</literal>. Note that you
	  probably don't want to specify <literal>border</literal> here, as
	  that is already taken care of by <literal>\pset border</literal>.
	  </para>
	  </listitem>
	  </varlistentry>


	  <varlistentry>
	  <term><literal>pager</literal></term>
	  <listitem>
	  <para>
	  Toggles the list of a pager to do table output. If the environment variable
	  <envar>PAGER</envar> is set, the output is piped to the specified program.
	  Otherwise <filename>more</filename> is used.
	  </para>

	  <para>
	  In any case, <application>psql</application> only uses the pager if it
	  seems appropriate. That means among other things that the output is to
	  a terminal and that the table would normally not fit on the screen.
	  Because of the modular nature of the printing routines it is not always
	  possible to predict the number of lines that will actually be printed.
	  For that reason <application>psql</application> might not appear very
	  discriminating about when to use the pager and when not to.
	  </para>
	  </listitem>
	  </varlistentry>
	</variablelist>
	Illustrations on how these different formats look can be seen in
	the <xref linkend="APP-PSQL-examples" endterm="APP-PSQL-examples-title"> section.
	</para>

	<tip>
	<para>
	There are various shortcut commands for <command>\pset</command>. See
	<command>\a</command>, <command>\C</command>, <command>\H</command>,
	<command>\t</command>, <command>\T</command>, and <command>\x</command>.
	</para>
	</tip>

	<note>
	<para>
	It is an error to call <command>\pset</command> without arguments. In the future
	this call might show the current status of all printing options.
	</para>
	</note>

	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\q</literal></term>
        <listitem>
        <para>
        Quit the <application>psql</application> program.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\qecho</literal> <replaceable class="parameter">text</replaceable> [ ... ] </term>
        <listitem>
        <para>
	This command is identical to <command>\echo</command> except that
	all output will be written to the query output channel, as set by
	<command>\o</command>.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\r</literal></term>
        <listitem>
        <para>
        Resets (clears) the query buffer.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\s</literal> [ <replaceable class="parameter">filename</replaceable> ]</term>
        <listitem>
        <para>
        Print or save the command line history to 
        <replaceable class="parameter">filename</replaceable>.
        If <replaceable class="parameter">filename</replaceable> is omitted,
	the history is written to the standard output.
        This option is only available if <application>psql</application> is
        configured to use the <acronym>GNU</acronym> history library.
        </para>

	<note>
	<para>
	As of <application>psql</application> version 7.0 it is no longer
	necessary to save the command history, since that will be done
	automatically on program termination. The history is
	also loaded automatically every time <application>psql</application>
	starts up.
	</para>
	</note>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\set</literal> [ <replaceable class="parameter">name</replaceable> [ <replaceable class="parameter">value</replaceable> [ ... ]]]</term>

	<listitem>
	<para>
	Sets the internal variable <replaceable class="parameter">name</replaceable>
	to <replaceable class="parameter">value</replaceable> or, if more than one
        value is given, to the concatenation of all of them. If no second argument
	is given, the variable is just set with no value. To unset a variable, use
        the <command>\unset</command> command.
	</para>

	<para>
	Valid variable names can contain characters, digits, and underscores.
        See the section about <application>psql</application> variables for details.
	</para>

	<para>
	Although you are welcome to set any variable to anything you want,
	<application>psql</application> treats several variables as special.
	They are documented in the section about variables.
	</para>

	<note>
	<para>
	This command is totally separate from the <acronym>SQL</acronym> command
	<xref linkend="SQL-SET" endterm="SQL-SET-title">.
	</para>
	</note>
	</listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\t</literal></term>
        <listitem>
        <para>
        Toggles the display of output column name headings and row count footer.
	This command is equivalent to <literal>\pset tuples_only</literal> and
	is provided for convenience.	
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\T</literal> <replaceable class="parameter">table_options</replaceable></term>
        <listitem>
        <para>
        Allows you to specify options to be placed within the <sgmltag>table</sgmltag>
	tag in <acronym>HTML</acronym> tabular output mode. This command is
	equivalent to <literal>\pset tableattr <replaceable class="parameter">table_options</replaceable></literal>.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\w</literal> {<replaceable class="parameter">filename</replaceable> | <replaceable class="parameter">|command</replaceable>}</term>
        <listitem>
        <para>
        Outputs the current query buffer to the file <replaceable class="parameter">filename</replaceable>
	or pipes it to the Unix command <replaceable class="parameter">command</replaceable>.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\x</literal></term>
        <listitem>
        <para>
        Toggles extended row format mode. As such it is equivalent to
	<literal>\pset expanded</literal>.
       </para>
       </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\z</literal> [ <replaceable class="parameter">pattern</replaceable> ]</term>
        <listitem>
        <para>
        Produces a list of all tables in the database with their appropriate
	access permissions listed. If an argument is given it is taken as a regular
	expression which limits the listing to those tables which match it.
        </para>

	<para>
<programlisting>
test=> <userinput>\z</userinput>
Access permissions for database "test"
 Relation |           Access permissions
----------+-------------------------------------
 my_table | {"=r","joe=arwR", "group staff=ar"}
(1 row )
</programlisting>
        Read this as follows:

	<itemizedlist>
          <listitem>
          <para>
          <literal>"=r"</literal>: <literal>PUBLIC</literal> has read
	  (<command>SELECT</command>) permission on the table.
	  </para>
	  </listitem>

	  <listitem>
	  <para>
	  <literal>"joe=arwR"</literal>: User <literal>joe</literal> has read,
	  write (<command>UPDATE</command>, <command>DELETE</command>),
	  <quote>append</quote> (<command>INSERT</command>) permissions,
	  and permission to create rules on the table.
	  </para>
	  </listitem>

	  <listitem>
	  <para>
	  <literal>"group staff=ar"</literal>: Group <literal>staff</literal>
	  has <command>SELECT</command> and <command>INSERT</command> permission.
	  </para>
	  </listitem>
	</itemizedlist>
	</para>

	<para>
	The commands <xref linkend="SQL-GRANT" endterm="SQL-GRANT-title"> and
	<xref linkend="SQL-REVOKE" endterm="SQL-REVOKE-title">
	are used to set access permissions.
	</para>

        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\!</literal> [ <replaceable class="parameter">command</replaceable> ]</term>
        <listitem>
        <para>
        Escapes to a separate Unix shell or executes the Unix command
        <replaceable class="parameter">command</replaceable>. The arguments
        are not further interpreted, the shell will see them as is.
        </para>
        </listitem>
      </varlistentry>


      <varlistentry>
        <term><literal>\?</literal></term>
        <listitem>
        <para>
        Get help information about the backslash (<quote>\</quote>) commands.
        </para>
        </listitem>
      </varlistentry>

    </variablelist>
  </para>
</refsect1>



<refsect1 id="R1-APP-PSQL-3">
  <refsect1info>
    <date>1998-09-26</date>
  </refsect1info>

  <title>Command-line Options</title>

  <para>
  If so configured, <application>psql</application> understands both standard
  Unix short options, and <acronym>GNU</acronym>-style long options. The latter
  are not available on all systems.
  </para>

  <para>
  <variablelist>
    <varlistentry>
      <term>-a, --echo-all</term>
      <listitem>
      <para>
      Print all the lines to the screen as they are read. This is more useful for
      script processing rather than interactive mode.
      This is equivalent to setting the variable <envar>ECHO</envar> to <literal>all</literal>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-A, --no-align</term>
      <listitem>
      <para>
      Switches to unaligned output mode. (The default output mode is otherwise
      aligned.)
      </para>
      </listitem>
    </varlistentry>

	
    <varlistentry>
      <term>-c, --command <replaceable class="parameter">query</replaceable></term>
      <listitem>
      <para>
      Specifies that <application>psql</application>
      is to execute one query string, <replaceable class="parameter">query</replaceable>,
      and then exit.  This is useful in shell scripts.
      </para>
      <para>
      <replaceable class="parameter">query</replaceable> must be either a query string
      that is completely parseable by the backend (i.e., it contains no <application>psql</application>
      specific features), or it is a single backslash command. Thus
      you cannot mix <acronym>SQL</acronym> and <application>psql</application>
      meta-commands. To achieve that, you could pipe the string into
      <application>psql</application>, like this:
      <literal>echo "\x \\ select * from foo;" | psql</literal>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-d, --dbname <replaceable class="parameter">dbname</replaceable></term>
      <listitem>
      <para>
      Specifies the name of the database to connect to. This is equivalent to specifying
      <replaceable class="parameter">dbname</replaceable> as the first non-option
      argument on the command line.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-e, --echo-queries</term>
      <listitem>
      <para>
      Show all queries that are sent to the backend.
      This is equivalent to setting the variable <envar>ECHO</envar>
      to <literal>queries</literal>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-E, --echo-hidden</term>
      <listitem>
      <para>
      Echoes the actual queries generated by \d and other backslash commands.
      You can use this if you wish to include similar functionality into
      your own programs. This is equivalent to setting the variable
      <envar>ECHO_HIDDEN</envar> from within <application>psql</application>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-f, --file <replaceable class="parameter">filename</replaceable></term>
      <listitem>
      <para>
      Use the file <replaceable class="parameter">filename</replaceable>
      as the source of queries instead of reading queries interactively.
      After the file is processed, <application>psql</application> terminates.
      This is in many ways equivalent to the internal command <command>\i</command>.
      </para>

      <para>
       If <replaceable>filename</replaceable> is <literal>-</literal>
       (hyphen), then standard input is read.
      </para>

      <para>
      Using this option is subtly different from writing
      <literal>psql &lt; <replaceable class="parameter">filename</replaceable></literal>.
      In general, both will do what you expect, but using <literal>-f</literal>
      enables some nice features such as error messages with line numbers.
      There is also a slight chance that using this option will reduce
      the start-up overhead. On the other hand, the variant using the shell's
      input redirection is (in theory) guaranteed to yield exactly the same
      output that you would have gotten had you entered everything by hand.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-F, --field-separator <replaceable class="parameter">separator</replaceable></term>
      <listitem>
      <para>
      Use <replaceable class="parameter">separator</replaceable> as the field separator.
      This is equivalent to <command>\pset fieldsep</command> or <command>\f</command>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-h, --host <replaceable class="parameter">hostname</replaceable></term>
      <listitem>
      <para>
      Specifies the host name of the machine on which the
      <application>postmaster</application> is running.
      If host begins with a slash, it is used 
      as the directory for the unix domain socket.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-H, --html</term>
      <listitem>
      <para>
      Turns on <acronym>HTML</acronym> tabular output. This is equivalent
      to <literal>\pset format html</literal> or the <command>\H</command>
      command.
      </para>
      </listitem>
    </varlistentry>

 
    <varlistentry>
      <term>-l, --list</term>
      <listitem>
      <para>
      Lists all available databases, then exits. Other non-connection options
      are ignored. This is similar to the internal command <command>\list</command>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-o, --output <replaceable class="parameter">filename</replaceable></term>
      <listitem>
      <para>
      Put all query output into file <replaceable class="parameter">filename</replaceable>.
      This is equivalent to the command <command>\o</command>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-p, --port <replaceable class="parameter">port</replaceable></term>
      <listitem>
      <para>
      Specifies the TCP/IP port or, by omission, the local Unix domain socket file
      extension on which the <application>postmaster</application>
      is listening for connections.  Defaults to the value of the
      <envar>PGPORT</envar> environment variable or, if not set, to the port
      specified at compile time, usually 5432.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-P, --pset <replaceable class="parameter">assignment</replaceable></term>
      <listitem>
      <para>
      Allows you to specify printing options in the style of <command>\pset</command>
      on the command line. Note that here you have to separate name and value with
      an equal sign instead of a space. Thus to set the output format to LaTeX, you
      could write <literal>-P format=latex</literal>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-q</term>
      <listitem>
      <para>
      Specifies that <application>psql</application> should do its work quietly.
      By default, it prints welcome messages and various informational output.
      If this option is used, none of this happens. This is useful with the
      <option>-c</option> option. Within <application>psql</application> you can
      also set the <envar>QUIET</envar> variable to achieve the same effect.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-R, --record-separator <replaceable class="parameter">separator</replaceable></term>
      <listitem>
      <para>
      Use <replaceable class="parameter">separator</replaceable> as the record separator.
      This is equivalent to the <command>\pset recordsep</command> command.
      </para>
      </listitem>
    </varlistentry>

 
    <varlistentry>
      <term>-s, --single-step</term>
      <listitem>
      <para>
      Run in single-step mode. That means the user is prompted before each query
      is sent to the backend, with the option to cancel execution as well.
      Use this to debug scripts.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-S, --single-line</term>
      <listitem>
      <para>
      Runs in single-line mode where a newline terminates a query, as a semicolon does.
      </para>

      <note>
      <para>
      This mode is provided for those who insist on it, but you are not necessarily
      encouraged to use it. In particular, if you mix <acronym>SQL</acronym> and
      meta-commands on a line the order of execution might not always be clear to
      the inexperienced user.
      </para>
      </note>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-t, --tuples-only</term>
      <listitem>
      <para>
      Turn off printing of column names and result row count footers, etc.
      It is completely equivalent to the <command>\t</command> meta-command.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-T, --table-attr <replaceable class="parameter">table_options</replaceable></term>
      <listitem>
      <para>
      Allows you to specify options to be placed within the <acronym>HTML</acronym>
      <sgmltag>table</sgmltag> tag. See <command>\pset</command> for details.
      </para>
      </listitem>
    </varlistentry>

 
    <varlistentry>
      <term>-u</term>
      <listitem>
      <para>
      Makes <application>psql</application> prompt for the user name and password
      before connecting to the database.
      </para>

      <para>
      This option is deprecated, as it is conceptually flawed. (Prompting for
      a non-default user name and prompting for a password because the
      backend requires it are really two different things.) You are encouraged
      to look at the <option>-U</option> and <option>-W</option> options instead.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-U, --username <replaceable class="parameter">username</replaceable></term>
      <listitem>
      <para>
      Connects to the database as the user <replaceable class="parameter">username</replaceable>
      instead of the default. (You must have permission to do so, of course.)
      </para> 
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-v, --variable, --set <replaceable class="parameter">assignment</replaceable></term>
      <listitem>
      <para>
      Performs a variable assignment, like the <command>\set</command>
      internal command.  Note that you must separate name and value,
      if any, by an equal sign on the command line. To unset a
      variable, leave off the equal sign.  To just set a variable
      without a value, use the equal sign but leave off the value.
      These assignments are done during a very early stage of
      start-up, so variables reserved for internal purposes might get
      overwritten later.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-V, --version</term>
      <listitem>
      <para>
      Shows the <application>psql</application> version.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-W, --password</term>
      <listitem>
      <para>
      Requests that <application>psql</application> should prompt for a password
      before connecting to a database. This will remain set for the entire
      session, even if you change the database connection with the meta-command
      <command>\connect</command>.
      </para>

      <para>
      As of version 7.0, <application>psql</application> automatically issues a
      password prompt whenever the backend requests password authentication.
      Because this is currently based on a hack, the automatic
      recognition might mysteriously fail, hence this option to force a prompt.
      If no password prompt is issued and the backend requires password authentication
      the connection attempt will fail.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-x, --expanded</term>
      <listitem>
      <para>
      Turns on extended row format mode. This is equivalent to the command
      <command>\x</command>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-X, --no-psqlrc</term>
      <listitem>
      <para>
      Do not read the start-up file <filename>~/.psqlrc</filename>.
      </para>
      </listitem>
    </varlistentry>


    <varlistentry>
      <term>-?, --help</term>
      <listitem>
      <para>
      Shows help about <application>psql</application> command line arguments.
      </para>
      </listitem>
    </varlistentry>

  </variablelist>
  </para>

</refsect1>


<refsect1 id="R1-APP-PSQL-4">
    <refsect1info>
      <date>1998-09-27</date>
    </refsect1info>

    <title>Advanced features</title>

  <refsect2 id="APP-PSQL-variables">
    <title id="APP-PSQL-variables-title">Variables</title>

    <para>
    <application>psql</application> provides variable substitution features
    similar to common Unix command shells. This feature is new and not very
    sophisticated, yet, but there are plans to expand it in the future.
    Variables are simply name/value
    pairs, where the value can be any string of any length. To set variables,
    use the <application>psql</application> meta-command <command>\set</command>:
<programlisting>
testdb=> <userinput>\set foo bar</userinput>
</programlisting>
    sets the variable <quote>foo</quote> to the value <quote>bar</quote>. To retrieve
    the content of the variable, precede the name with a colon and use it
    as the argument of any slash command:
<programlisting>
testdb=> <userinput>\echo :foo</userinput>
bar
</programlisting>
    </para>

    <note>
    <para>
    The arguments of <command>\set</command> are subject to the same substitution
    rules as with other commands. Thus you can construct interesting references
    such as <literal>\set :foo 'something'</literal> and get <quote>soft
    links</quote> or <quote>variable variables</quote> of <productname>Perl</productname>
    or <productname><acronym>PHP</acronym></productname> fame, respectively.
    Unfortunately (or fortunately?), there is no way to do anything useful
    with these constructs. On the
    other hand, <literal>\set bar :foo</literal> is a perfectly valid way to copy
    a variable.
    </para>
    </note>

    <para>
    If you call <command>\set</command> without a second argument, the variable is simply
    set, but has no value. To unset (or delete) a variable, use the command
    <command>\unset</command>.
    </para>

    <para>
    <application>psql</application>'s internal variable names can consist of
    letters, numbers, and underscores in any order and any number of them.
    A number of regular variables are treated specially by <application>psql</application>.
    They indicate certain option settings that can be changed at runtime
    by altering the value of the variable or represent some state of the application.
    Although you can use these
    variables for any other purpose, this is not recommended, as the
    program behavior might grow really strange really quickly.
    By convention, all specially treated variables consist of all upper-case letters
    (and possibly numbers and underscores). To ensure maximum compatibility in the
    future, avoid such variables. 
    A list of all specially treated variables follows.
    <variablelist>
      <varlistentry>
        <term><envar>DBNAME</envar></term>
	<listitem>
	<para>
        The name of the database you are currently connected to. This is set every time
        you connect to a database (including program start-up), but can be unset.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>ECHO</envar></term>
	<listitem>
	<para>
	If set to <quote><literal>all</literal></quote>, all lines entered or from a script
        are written to the standard output before they
	are parsed or executed. To specify this on program start-up, use the switch
        <option>-a</option>. If set to <quote><literal>queries</literal></quote>,
        <application>psql</application> merely prints all queries as they are sent to the
        backend. The option for this is <option>-e</option>.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>ECHO_HIDDEN</envar></term>
	<listitem>
	<para>
	When this variable is set and a backslash command queries the database, the query
	is first shown. This way you can study the <productname>Postgres</productname>
	internals and provide similar functionality in your own programs. If you set the
	variable to the value <quote>noexec</quote>, the queries are just shown but are
	not actually sent to the backend and executed.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>ENCODING</envar></term>
	<listitem>
	<para>
        The current client multibyte encoding. If you are not set up to use
        multibyte characters, this variable will always contain
        <quote>SQL_ASCII</quote>.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>HISTCONTROL</envar></term>
	<listitem>
	<para>
         If  this variable is set  to  <literal>ignorespace</literal>, lines which begin with a
         space are not entered into the history list. If set to a value of
         <literal>ignoredups</literal>, lines matching the previous history line are not
         entered. A value of <literal>ignoreboth</literal> combines the two
         options.  If unset, or if set to any other value than those above, all lines read
         in interactive mode are saved on the history list.
	</para>
        <note>
        <para>
        This feature was shamelessly plagiarized from <application>bash</application>.
        </para>
        </note>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>HISTSIZE</envar></term>
	<listitem>
	<para>
        The number of commands to store in the command history.
        The default value is 500.
	</para>
        <note>
        <para>
        This feature was shamelessly plagiarized from <application>bash</application>.
        </para>
        </note>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>HOST</envar></term>
	<listitem>
	<para>
        The database server host you are currently connected to. This is set every time
        you connect to a database (including program start-up), but can be unset.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>IGNOREEOF</envar></term>
	<listitem>
	<para>
         If unset, sending an EOF character (usually Control-D) to an interactive session of
         <application>psql</application> will terminate the application.
         If set to a numeric value, that many EOF characters are ignored before the application
         terminates. If the variable is set but has no numeric value, the default is 10.
	</para>
        <note>
        <para>
        This feature was shamelessly plagiarized from <application>bash</application>.
        </para>
        </note>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>LASTOID</envar></term>
	<listitem>
	<para>
        The value of the last affected oid, as returned from an <command>INSERT</command>
        or <command>lo_insert</command> command. This variable is only guaranteed to be
        valid until after the result of the next <acronym>SQL</acronym> command has been
        displayed.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>LO_TRANSACTION</envar></term>
	<listitem>
	<para>
	If you use the <productname>Postgres</productname> large object
        interface to specially store data that does not fit into one tuple,
        all the operations must be contained in a transaction block. (See the
        documentation of the large object interface for more information.) Since
        <application>psql</application> has no way to tell if you already
        have a transaction in progress when you call one of its internal
        commands (<command>\lo_export</command>, <command>\lo_import</command>,
        <command>\lo_unlink</command>) it must take some arbitrary action. This
        action could either be to roll back any transaction that might already
        be in progress, or to commit any such transaction, or to do nothing at
        all. In the last case you must provide your own
        <command>BEGIN TRANSACTION</command>/<command>COMMIT</command> block or
        the results will be unpredictable (usually resulting in the desired
        action's not being performed in any case).
	</para>

	<para>
	To choose what you want to do you set this variable to one of
	<quote>rollback</quote>, <quote>commit</quote>, or <quote>nothing</quote>.
        The default is to roll back the transaction. If you just want to load one
        or a few objects this is fine. However, if you intend to transfer many
        large objects, it might be advisable to provide one explicit transaction
        block around all commands.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>ON_ERROR_STOP</envar></term>
	<listitem>
	<para>
	By default, if non-interactive scripts encounter an error, such as a
	malformed <acronym>SQL</acronym> query or internal meta-command,
	processing continues. This has been the traditional behavior of
        <application>psql</application> but it is sometimes not desirable. If this variable
	is set, script processing will immediately terminate. If the script was
	called from another script it will terminate in the same fashion.
	If the outermost script was not called from an interactive <application>psql</application>
	session but rather using the <option>-f</option> option, <application>psql</application>
	will return error code 3, to distinguish this case from fatal
	error conditions (error code 1).
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>PORT</envar></term>
	<listitem>
	<para>
        The database server port to which you are currently connected. This is set every time
        you connect to a database (including program start-up), but can be unset.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>PROMPT1</envar>, <envar>PROMPT2</envar>, <envar>PROMPT3</envar></term>
	<listitem>
	<para>
	These specify what the prompt <application>psql</application> issues is
	supposed to look like. See
	<quote><xref linkend="APP-PSQL-prompting" endterm="APP-PSQL-prompting-title"></quote>
	below.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>QUIET</envar></term>
	<listitem>
	<para>
	This variable is equivalent to the command line option <option>-q</option>.
	It is probably not too useful in interactive mode.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>SINGLELINE</envar></term>
	<listitem>
	<para>
	This variable is set by the command line option <option>-S</option>. You
	can unset or reset it at run time.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>SINGLESTEP</envar></term>
	<listitem>
	<para>
	This variable is equivalent to the command line option <option>-s</option>.
	</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><envar>USER</envar></term>
	<listitem>
	<para>
        The database user you are currently connected as. This is set every time
        you connect to a database (including program start-up), but can be unset.
	</para>
	</listitem>
      </varlistentry>

    </variablelist>

    </para>

  </refsect2>


  <refsect2 id="APP-PSQL-sql-interpol">
    <title id="APP-PSQL-sql-interpol-title"><acronym>SQL</acronym> Interpolation</title>

    <para>
    An additional useful feature of <application>psql</application> variables
    is that you can substitute (<quote>interpolate</quote>) them into
    regular <acronym>SQL</acronym> statements. The syntax for this is again to prepend
    the variable name with a colon (<literal>:</literal>).
<programlisting>
testdb=> <userinput>\set foo 'my_table'</userinput>
testdb=> <userinput>SELECT * FROM :foo;</userinput>
</programlisting>
    would then query the table <literal>my_table</literal>. The value of the
    variable is copied literally, so it can even contain unbalanced quotes or
    backslash commands. You must make sure that it makes sense where you put it.
    Variable interpolation will not be performed into quoted <acronym>SQL</acronym>
    entities.
    </para>

    <para>
    A popular application of this facility is to refer to the last inserted
    <acronym>OID</acronym> in subsequent statements to build a foreign key
    scenario.
    Another possible use of this mechanism is to copy the contents of a file
    into a field. First load the file into a variable and then proceed as above.
<programlisting>
testdb=> <userinput>\set content '\'' `cat my_file.txt` '\''</userinput>
testdb=> <userinput>INSERT INTO my_table VALUES (:content);</userinput>
</programlisting>
    One possible problem with this approach is that <filename>my_file.txt</filename>
    might contain single quotes. These need to be escaped so that
    they don't cause a syntax error when the third line is processed. This
    could be done with the program <application>sed</application>:
<programlisting>
testdb=> <userinput>\set content `sed -e "s/'/\\\\\\'/g" < my_file.txt`</userinput>
</programlisting>
    Observe the correct number of backslashes (6)! You can resolve it this way: After
    <application>psql</application> has parsed this line, it passes
    <literal>sed -e "s/'/\\\'/g" < my_file.txt</literal> to the shell. The shell
    will do its own thing inside the double quotes and execute <filename>sed</filename>
    with the arguments <literal>-e</literal> and <literal>s/'/\\'/g</literal>.
    When <application>sed</application> parses this it will replace the two
    backslashes with a single one and then do the substitution. Perhaps at
    one point you thought it was great that all Unix commands use the same
    escape character. And this is ignoring the fact that you might have to
    escape all backslashes as well because <acronym>SQL</acronym> text constants
    are also subject to certain interpretations. In that case you might
    be better off preparing the file externally.
    </para>

    <para>
    Since colons may legally appear in queries, the following rule applies: If the variable
    is not set, the character sequence <quote>colon+name</quote> is not changed. In any
    case you can escape a colon with a backslash to protect it from interpretation.
    (The colon syntax for variables is standard <acronym>SQL</acronym> for embedded
    query languages, such as <application>ecpg</application>. The colon syntax for
    array slices and type casts are <productname>Postgres</productname> extensions,
    hence the conflict.)
    </para>

  </refsect2>


  <refsect2 id="APP-PSQL-prompting">
    <title id="APP-PSQL-prompting-title">Prompting</title>

    <para>
    The prompts <application>psql</application> issues can be customized to
    your preference. The three variables <envar>PROMPT1</envar>, <envar>PROMPT2</envar>,
    and <envar>PROMPT3</envar> contain strings and special escape sequences
    that describe the appearance of the prompt. Prompt 1 is the normal prompt
    that is issued when <application>psql</application> requests a new query.
    Prompt 2 is issued when more input is expected during query input because
    the query was not terminated with a semicolon or a quote was not closed.
    Prompt 3 is issued when you run an <acronym>SQL</acronym> <command>COPY</command>
    command and you are expected to type in the tuples on the terminal.
    </para>

    <para>
    The value of the respective prompt variable is printed literally, except where
    a percent sign (<quote>%</quote>) is encountered. Depending on the next
    character, certain other text is substituted instead. Defined substitutions are:

    <variablelist>
      <varlistentry>
        <term><literal>%M</literal></term>
	<listitem>
         <para>
          The full hostname (with domain name) of the database server,
          or <literal>[local]</literal> if the connection is over a
          Unix domain socket, or
          <literal>[local:<replaceable>/dir/name</replaceable>]</literal>,
          if the Unix domain socket is not at the compiled in default
          location.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%m</literal></term>
	<listitem>
         <para>
          The hostname of the database server, truncated after the
          first dot, or <literal>[local]</literal> if the connection
          is over a Unix domain socket.
         </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%&gt;</literal></term>
	<listitem><para>The port number at which the database server is listening.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%n</literal></term>
	<listitem><para>The username you are connected as (not your local system
         user name).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%/</literal></term>
	<listitem><para>The name of the current database.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%~</literal></term>
	<listitem><para>Like <literal>%/</literal>, but the output is <quote>~</quote>
         (tilde) if the database is your default database.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%#</literal></term>
	<listitem><para>If the current user is a database superuser, then a
         <quote>#</quote>, otherwise a <quote>&gt;</quote>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%R</literal></term>
	<listitem><para>
	In prompt 1 normally <quote>=</quote>, but <quote>^</quote> if in single-line
        mode, and <quote>!</quote> if the session is disconnected from the database
        (which can happen if <command>\connect</command> fails). In prompt 2 the
        sequence is replaced by <quote>-</quote>, <quote>*</quote>, a single quote,
	or a double quote, depending on whether <application>psql</application>
        expects more input because the query wasn't terminated yet, because you are
        inside a <literal>/* ... */</literal> comment, or because you are inside
        a quote. In prompt 3 the sequence doesn't resolve to anything.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%</literal><replaceable class="parameter">digits</replaceable></term>
	<listitem><para>
	If <replaceable class="parameter">digits</replaceable> starts with
        <literal>0x</literal> the rest of the characters are interpreted as a
        hexadecimal digit and the character with the corresponding code is
        substituted. If the first digit is <literal>0</literal> the characters are
        interpreted as on octal number and the corresponding character is
        substituted. Otherwise a decimal number is assumed.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%:</literal><replaceable class="parameter">name</replaceable><literal>:</literal></term>
	<listitem><para>
	The value of the <application>psql</application>, variable <replaceable
        class="parameter">name</replaceable>. See the section
	<quote><xref linkend="APP-PSQL-variables" endterm="APP-PSQL-variables-title"></quote>
	for details.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>%`</literal><replaceable class="parameter">command</replaceable><literal>`</literal></term>
	<listitem><para>
	The output of <replaceable class="parameter">command</replaceable>, similar to
	ordinary <quote>back-tick</quote> substitution.</para>
	</listitem>
      </varlistentry>

    </variablelist>

    To insert a percent sign into your prompt, write <literal>%%</literal>. The
    default prompts are equivalent to <literal>'%/%R%# '</literal> for prompts 1
    and 2, and <literal>'&gt;&gt; '</literal> for prompt 3.
    </para>

    <note>
    <para>
    This feature was shamelessly plagiarized from <application>tcsh</application>.
    </para>
    </note>

   </refsect2>

  <refsect2 id="APP-PSQL-MISC">
    <title id="APP-PSQL-MISC-title">Miscellaneous</title>

    <para>
    <application>psql</application> returns 0 to the shell if it finished normally,
    1 if a fatal error of its own (out of memory, file not found) occurs, 2 if the
    connection to the backend went bad and the session is not interactive, and 3 if
    an error occurred in a script and the variable <envar>ON_ERROR_STOP</envar> was
    set.
    </para>

    <para>
    Before starting up, <application>psql</application> attempts
    to read and execute commands from the file <filename>$HOME/.psqlrc</filename>. It
    could be used to set up the client or the server to taste (using the <command>\set
    </command> and <command>SET</command> commands).
    </para>

  </refsect2>

  <refsect2>
    <title><acronym>GNU</acronym> readline</title>

    <para>
    <application>psql</application> supports the readline and history libraries for
    convenient line editing and retrieval. The command history is stored in a file
    named <filename>.psql_history</filename> in your home directory and is reloaded when
    <application>psql</application> starts up.
    Tab-completion is also supported, although
    the completion logic makes no claim to be an <acronym>SQL</acronym> parser.
    When available, <application>psql</application> is automatically built to use these
    features. If for some reason you do not like the tab completion, you can turn if off
    by putting this in a file named <filename>.inputrc</filename> in your
    home directory:
<programlisting>
$if psql
set disable-completion on
$endif
</programlisting>
    (This is not a <application>psql</application> but a <application>readline</application>
    feature. Read its documentation for further details.)
    </para>

    <para>
    If you have the readline library installed but <application>psql</application>
    does not seem to use it, you must make sure that <productname>Postgres</productname>'s
    top-level <filename>configure</filename> script finds it. <filename>configure</filename>
    needs to find both the library <filename>libreadline.a</filename>
    (or a shared library equivalent)
    <emphasis>and</emphasis> the header files <filename>readline.h</filename> and
    <filename>history.h</filename> (or <filename>readline/readline.h</filename> and
    <filename>readline/history.h</filename>) in appropriate directories. If
    you have the library and header files installed in an obscure place you
    must tell <filename>configure</filename> about them, for example:
<programlisting>
$ ./configure --with-includes=/opt/gnu/include --with-libs=/opt/gnu/lib  ...
</programlisting>
    Then you have to recompile <application>psql</application> (not necessarily
    the entire code tree).
    </para>

    <para>
    The <acronym>GNU</acronym> readline library can be obtained from the <acronym>GNU</acronym>
    project's <acronym>FTP</acronym> server at <ulink URL="ftp://ftp.gnu.org">ftp://ftp.gnu.org</ulink>.
    </para>
  </refsect2>



</refsect1>


<refsect1 id="APP-PSQL-examples">
  <title id="APP-PSQL-examples-title">Examples</title>

  <note>
  <para>
  This section only shows a few examples specific to <application>psql</application>.
  If you want to learn <acronym>SQL</acronym> or get familiar with
  <productname>Postgres</productname>, you might wish to read the Tutorial that
  is included in the distribution.
  </para>
  </note>

  <para>
  The first example shows how to spread a query over several lines of input.
  Notice the changing prompt:
<programlisting>
testdb=> <userinput>CREATE TABLE my_table (</userinput>
testdb(> <userinput> first integer not null default 0,</userinput>
testdb(> <userinput> second text</userinput>
testdb-> <userinput>);</userinput>
CREATE
</programlisting>
  Now look at the table definition again:
<programlisting>
testdb=> <userinput>\d my_table</userinput>
             Table "my_table"
 Attribute |  Type   |      Modifier
-----------+---------+--------------------
 first     | integer | not null default 0
 second    | text    |

</programlisting>
  At this point you decide to change the prompt to something more
  interesting:
<programlisting>
testdb=> <userinput>\set PROMPT1 '%n@%m %~%R%# '</userinput>
peter@localhost testdb=>
</programlisting>
  Let's assume you have filled the table with data and want to take a look at it:
<programlisting>
peter@localhost testdb=> SELECT * FROM my_table;
 first | second
-------+--------
     1 | one
     2 | two
     3 | three
     4 | four
(4 rows)

</programlisting>
  You can make this table look differently by using the <command>\pset</command>
  command:
<programlisting>
peter@localhost testdb=> <userinput>\pset border 2</userinput>
Border style is 2.
peter@localhost testdb=> <userinput>SELECT * FROM my_table;</userinput>
+-------+--------+
| first | second |
+-------+--------+
|     1 | one    |
|     2 | two    |
|     3 | three  |
|     4 | four   |
+-------+--------+
(4 rows)

peter@localhost testdb=> <userinput>\pset border 0</userinput>
Border style is 0.
peter@localhost testdb=> <userinput>SELECT * FROM my_table;</userinput>
first second
----- ------
    1 one
    2 two
    3 three
    4 four
(4 rows)

peter@localhost testdb=> <userinput>\pset border 1</userinput>
Border style is 1.
peter@localhost testdb=> <userinput>\pset format unaligned</userinput>
Output format is unaligned.
peter@localhost testdb=> <userinput>\pset fieldsep ","</userinput>
Field separator is ",".
peter@localhost testdb=> <userinput>\pset tuples_only</userinput>
Showing only tuples.
peter@localhost testdb=> <userinput>SELECT second, first FROM my_table;</userinput>
one,1
two,2
three,3
four,4
</programlisting>
  Alternatively, use the short commands:
<programlisting>
peter@localhost testdb=> <userinput>\a \t \x</userinput>
Output format is aligned.
Tuples only is off.
Expanded display is on.
peter@localhost testdb=> <userinput>SELECT * FROM my_table;</userinput>
-[ RECORD 1 ]-
first  | 1
second | one
-[ RECORD 2 ]-
first  | 2
second | two
-[ RECORD 3 ]-
first  | 3
second | three
-[ RECORD 4 ]-
first  | 4
second | four
</programlisting>
  </para>

</refsect1>


<refsect1>
  <refsect1info>
    <date>1999-10-27</date>
  </refsect1info>

  <title>Appendix</title>

  <refsect2>
    <title>Bugs and Issues</title>

    <itemizedlist>
      <listitem>
      <para>
      In some earlier life <application>psql</application> allowed the first
      argument to start directly after the (single-letter) command. For
      compatibility this is still supported to some extent but I am not
      going to explain the details here as this use is discouraged. But
      if you get strange messages, keep this in mind. For example
<programlisting>
testdb=> <userinput>\foo</userinput>
Field separator is "oo",
</programlisting>
      which is perhaps not what one would expect.
      </para>
      </listitem>

      <listitem>
      <para>
      <application>psql</application> only works smoothly with servers of the
      same version. That does not mean other combinations will fail outright,
      but subtle and not-so-subtle problems might come up.
      </para>
      </listitem>

      <listitem>
      <para>
      Pressing Control-C during a <quote>copy in</quote> (data sent to the
      server) doesn't show the most ideal of behaviors. If you get a message
      such as <quote>PQexec: you gotta get out of a COPY state yourself</quote>,
      simply reset the connection by entering <literal>\c - -</literal>.
      </para>
      </listitem>

    </itemizedlist>

  </refsect2>

</refsect1>

</refentry>

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