.. index::
   single: Variable substitution

.. _variable_sub:

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 Variable Substitution
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Syntax: '%' + variable name + '%'

.. seealso::

  :ref:`runsub`.

**Example 1**. Connecting securely to a Spatial Database

You want to map some senstitive data held in a PostGIS database. The username 
and password to be used for the database connection are held in 2 cookies 
previously set by a seperate authentication mechanism, "uid" and "passwd".

.. code-block:: mapfile

  CONNECTION "user=%uid% password=%passwd% dbname=postgis"

**Example 2**. Handling temporary files

You have a user based discovery application that generates shapefiles and 
stores them in a user's home directory on the server. The "username" comes 
from a cookie, the "filename" comes from a request parameter.

.. code-block:: mapfile

  DATA "/home/%username%/tempshp/%filename%"

This feature is only available in the CGI version of MapServer through a 
mapfile pre-processor. If you are using MapScript, you will have to code 
the substitution logic into your application yourself (By writing your 
own pre-processor).