interpolation (that is, <literal>:name</literal>,
    <literal>:'name'</literal>, or <literal>:"name"</literal>) is not
    replaced unless the named variable is currently set. In any case, you
    can escape a colon with a backslash to protect it from substitution.
    </para>

    <para>
    The <literal>:{?<replaceable>name</replaceable>}</literal> special syntax returns TRUE
    or FALSE depending on whether the variable exists or not, and is thus
    always substituted, unless the colon is backslash-escaped.
    </para>

    <para>
    The colon syntax for variables is standard <acronym>SQL</acronym> for
    embedded query languages, such as <application>ECPG</application>.
    The colon syntaxes for array slices and type casts are
    <productname>PostgreSQL</productname> extensions, which can sometimes
    conflict with the standard usage.  The colon-quote syntax for escaping a
    variable's value as an SQL literal or identifier is a
    <application>psql</application> extension.
    </para>

   </refsect3>

   <refsect3 id="app-psql-prompting" xreflabel="Prompting">
    <title>Prompting</title>

    <para>
    The prompts <application>psql</application> issues can be customized
    to your preference. The three variables <varname>PROMPT1</varname>,
    <varname>PROMPT2</varname>, and <varname>PROMPT3</varname> 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 command. Prompt 2 is
    issued when more input is expected during command entry, for example
    because the command was not terminated with a semicolon or a quote
    was not closed.
    Prompt 3 is issued when you are running an <acronym>SQL</acronym>
    <command>COPY FROM STDIN</command> command and you need to type in
    a row value on the terminal.
    </para>

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

    <variablelist>
      <varlistentry id="app-psql-prompting-m-uc">
        <term><literal>%M</literal></term>
        <listitem>
         <para>
          The full host name (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 id="app-psql-prompting-m-lc">
        <term><literal>%m</literal></term>
        <listitem>
         <para>
          The host name of the database server, truncated at the
          first dot, or <literal>[local]</literal> if the connection is
          over a Unix domain socket.
         </para>
        </listitem>
      </varlistentry>

      <varlistentry id="app-psql-prompting-gt">
        <term><literal>%&gt;</literal></term>
        <listitem><para>The port number at which the database server is listening.</para></listitem>
      </varlistentry>

      <varlistentry id="app-psql-prompting-n">
        <term><literal>%n</literal></term>
        <listitem>
         <para>
          The database session user name.  (The expansion of this
          value might change during a database session as the result
          of the command <command>SET SESSION
          AUTHORIZATION</command>.)
         </para>
        </listitem>
      </varlistentry>

      <varlistentry id="app-psql-prompting-s">
        <term><literal>%s</literal></term>
        <listitem><para>The name of the service.</para></listitem>
      </varlistentry>

      <varlistentry id="app-psql-prompting-slash">
        <term><literal>%/</literal></term>
        <listitem><para>The