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Dynamic variables behave like "normal" static variables defined by the <variable> tag, except that they are evaluated on each panel change. They are maintained as normal variables in an installation process, but in comparison to them dynamic variables have been enhanced by many more facilities. You can set dynamic variables values from the following sources on the target computer:

  • plain values
  • environment variables
  • INI files
  • option/property files (key-value pairs)
  • XML files (using XPath-like queries)
  • INI/option/XML files from within an ZIP or JAR file
  • Windows registry
  • output of a command execution

and filter them optionally using regular expressions. A particular dynamic variable can be evaluated based on a certain condition.

Other variables and dynamic variables can be used within ${ and } to be replaced in the assignment expressions below.

Common attributes to all types of dynamic variables are:

  • name
    The name of the dynamic variable to refer to it from panels, in variable substitution and so on. Since dynamic variables are saved like a normal variable (as $INSTALL_PATH), they can be accessed like any other variable from within an IzPack installer.
  • checkonce := "true" | "false" (optional, defaults to "false")
    Might be added to assign a dynamic variable only one time at the beginning of the installation process, which makes it behave as a normal variable, although with enhanced capabilities to gather a value.
  • ignorefailure := "true" | "false" (optional, defaults to "false")
    Might be used to allow the installation to continue or abort if an error occurred during gathering the value for a certain dynamic variable.
  • condition (optional)
    The assignment of a dynamic variable itself can be made dependent on a certain condition, using the condition attribute, which refers to the ID of condition defined in the installer description elsewhere.

Types of Dynamic Variable Assignments

Plain Values

The easiest way to assign a value to a dynamic variable is a plain value.

Using a plain dynamic variable assignment is recognized by using the attribute value in the variable definition.

Specific attributes:

  • value
    The plain value to be assigned to the dynamic variable.

Example:

Code Block
titleAssigning a plain value to a dynamic variable
langxml
<dynamicvariables>
    <variable name="previous.version" value="4.3.3"/>
</dynamicvariable>

The above example is functionally equivalent to

Code Block
langxml
<variables>
    <variable name="previous.version" value="4.3.3"/>
</variable>

since there are no replacements used which might be refreshed on a panel change.

Plain Values as Embedded Text

In another addition to normal variables, the value of a variable can be also defined using a nested value element embedding plain text

Example:

To comment out something in a xml file if a certain pack with the ID "mycoolfeature" is not activated, you might alternate between one and the same variable name, which gets assigned different values in different conditions.

Code Block
xml
xml
<dynamicvariables>

    <variable name="XML_Comment_Start" condition="\!izpack.selected.mycoolfeature">
        <value><\!\[CDATA[<!--]\]></value>
    </variable>
    <variable name="XML_Comment_End" condition="\!izpack.selected.mycoolfeature">
        <value><\!\[CDATA[-->]\]></value>
    </variable>

    <variable name="XML_Comment_Start" value="" condition="izpack.selected.mycoolfeature" />
    <variable name="XML_Comment_End" value="" condition="izpack.selected.mycoolfeature" />

</dynamicvariables>

The condition "izpack.selected.mycoolfeature" is generated automatically when a pack with the ID "mycoolfeature" was specified. You could now use ${XML_Comment_Start} and ${XML_Comment_End} in a file which should be parsed.

Values from Environment Variables

Using a  dynamic variable assignment from an environment variable is recognized by using the attribute environment in the variable definition.

Specific attributes:

  • environment
    The name of the environment variable to get the assignment value from.
Code Block
titleAssigning the value of an environment variable to a dynamic variable
langxml
<dynamicvariables>
    <variable name="search.path" environment="PATH"/>
</dynamicvariables>

The above example is functionally equivalent to

Code Block
langxml
<variables>
    <variable name="search.path" value="${ENV[PATH]}"/>
</variable>

since there are no replacements used which might be refreshed on a panel change and the environment variable PATH won't change during the runtime of an installation process.

Values from Property/Option Files

Dynamic variables can be also assigned from a value in configuration files with key-value pairs, as property files.

Using a  dynamic variable assignment from a certain option or property of an option or property file is recognized by using the attribute file in the variable definition along with the attribute type set to "options" (or left out).

Specific attributes:

  • file
    The property/option file path to read from.
  • type := "options" | "ini" | "xml" (optional, defaults to "options")
    The file type, must be "options" to read options or properties.
  • key
    The option or property key to read the value for.
  • escape := "true" | "false" (optional: defaults to "true")
    Whether to apply escape sequences escaped by backslashes, like defined for Java properties files.
    Set "false" especially if you want to read values with backslashes where backslashes are not assumed to introduce escape sequences, like Windows paths.

The attribute type="options" is to be used to make this file parsed as an option file. Separators between the key and value might be for instance '=', ':' including their escaped variants '\=', '\:', where leading and trailing whitespaces are trimmed off.

Example:

Code Block
titleAssigning a dynamic variable from properties/option files
langxml
<dynamicvariables>

    <variable name="option.1" checkonce="true"
              file="${INSTALL_PATH}/../old_installation/test.properties" type="options"
              key="first.setting"/>

    <variable name="option.2" checkonce="true"
              file="${INSTALL_PATH}/../old_installation/test.conf" type="options"
              key="work.dir"/>

</dynamicvariables>

Values from INI Files

It's also possible to assign Windows INI file values to IzPack dynamic variables. INI files are 3-dimensional configuration files with key-value pairs which are divided into several sections, following a certain syntax.

Using a dynamic variable assignment from a certain entry of an INI file is recognized by using the attribute file in the variable definition along with the attribute type set to "ini".

Specific attributes:

  • file
    The INI file path to read from.
  • type := "options" | "ini" | "xml" (optional, defaults to "options")
    The file type, must be "ini" to read INI keys.
  • section
    The INI section to lookup the entry in.
  • key
    The INI entry key to read the value for.
  • escape := "true" | "false" (optional: defaults to "true")
    Whether to apply escape sequences escaped by backslashes, like defined for Java properties files.
    Set "false" especially if you want to read values with backslashes where backslashes are not assumed to introduce escape sequences, like Windows paths.

Example:

Code Block
titleAssigning a dynamic variable from an INI file value
langxml
<dynamicvariables>
    <variable name="ini.1" checkonce="true"
              file="C:/Program Files/freesshd/FreeSSHDService.ini" type="ini"
              section="SSH server" key="SSHCMD"/>
</dynamicvariables>

Values from XML Files

Another facility of dynamic variable assignments is reading values from XML files using XPath queries. For the syntax of XPath see XML Path Language (XPath) for more information.

Using a dynamic variable assignment from a certain XML entry in a XML file is recognized by using the attribute file in the variable definition along with the attribute type set to "xml".

Specific attributes:

  • file
    The XML file path to read from.
  • type := "options" | "ini" | "xml" (optional, defaults to "options")
    The file type, must be "xml" to assume a XML file.
  • key
    The XPath path to the entry to read the value for.
    Note: Currently, the XPath language revision depends on the JRE version the installer runs on. JRE 6/7 support XPath 1.0.

Example:

Code Block
titleDynamic variable assignment from XML file contents
langxml
<dynamicvariables>

    <variable name="XMLReadTest.1" checkonce="true" ignorefailure="false"
              file="${INSTALL_PATH}/../old_installation/test.xml" type="xml"
              key="/installations/installation[path='/usr/local']/title[@lang='en']/text()"/>

    <variable name="XMLReadTest.2" checkonce="true" ignorefailure="false"
              file="${INSTALL_PATH}/../old_installation/test.xml" type="xml"
              key="//title[@lang='en']/text()"/>

</dynamicvariables>

Values From Configuration Files in an Archive (JAR/ZIP)

All of the above variants of reading a dynamic variable value from a configuration file can be also applied if that configuration files is packaged as an entry into a ZIP or JAR file.

Using a dynamic variable assignment from a certain entry of a configuration file packed into an archive is recognized by using the attributes jarfile or zipfile in the variable definition.

Specific attributes:

  • jarfile
    The jar file path to read from.
  • zipfile
    The zip file path to read from.
  • type := "options" | "ini" | "xml" (optional, defaults to "options")
    The archived file's type.
  • section
    The INI section to lookup the entry in, is evaluated only if type = "ini".
  • key
    The INI, option or property entry key to read the value for.
  • escape := "true" | "false" (optional: defaults to "true")
    Whether to apply escape sequences escaped by backslashes, like defined for Java properties files.
    Set "false" especially if you want to read values with backslashes where backslashes are not assumed to introduce escape sequences, like Windows paths.

Example:

Code Block
titleAssigning a dynamic variable from an configuration entry in a JAR/ZIP file
langxml
<dynamicvariables>

    <variable name="previous.version" jarfile="${INSTALL_PATH}/${INSTALL_SUBPATH}/libs/config.jar"
              entry="release.properties" type="options"
              key="release.version"
              checkonce="false" ignorefailure="true">
    </variable>

    <variable name="other.stuff" zipfile="${INSTALL_PATH}/${INSTALL_SUBPATH}/libs/misc.zip"
              entry="app.ini" type="ini"
              section="Global Settings" key="AUTOSTART"
              checkonce="true" ignorefailure="true">
    </variable>

</dynamicvariables>

Values from the Windows Registry

Dynamic variable values can be also gathered from Windows registry data.

Using a dynamic variable assignment from a registry entry is recognized by using the attribute regkey in the variable definition.

Specific attributes:

  • regkey
    The registry entry root key to find the registry value to read from.
  • regvalue
    The registry value to read from, which is in Microsoft terms equivalent to a key in ordinary INI files.

Example:

Code Block
titleAssigning a dynamic variable value from the Windows registry
langxml
<dynamicvariables>
    <variable name="RegistryReadTest" checkonce="true"
              regkey="HKLM\\SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Environment"
              regvalue="Path"/>
</dynamicvariables>

Values from the Output of a Command Execution

Last but not least, a dynamic variable value can be assigned from the output of an external command execution.

Using a dynamic variable assignment from command output is recognized by using the attribute executable in the variable definition.

Specific attributes:

  • executable
    Absolute or relative path to the command to be launched. If the "dir" attribute is used, than relative paths are computed against the mentioned directory. The characters '.' and '..' inside the command path are resolved to a canonical path according to the operating system.
  • type := "process" | "shell" (optional, defaults to "process")
    "process" - launch the command directly without an underlying shell invocation
    "shell" - launch the command over the system shell, assuming it to be a shell script
  • dir (optional)
    Absolute or relative path to a work directory, from where the command should be launched. The characters '.' and '..' inside the directory path are resolved to a canonical path according to the operating system.
  • stderr := "true" | "false" (optional, defaults to "false")
    Whether the standard error output of the command should be used instead of the standard output.
    This can be useful for some commands which deliver certain information only as error, for instance 'java -version'..

Example 1:

Code Block
titleAssigning a dynamic variable value from the output of a command execution
langxml
<dynamicvariables>

    <variable name="hostname" checkonce="true"
              executable="hostname"
              type="process"/>

    <variable name="result.value" checkonce="true"
              executable="${INSTALL_PATH}/bin/init.sh"
              type="shell"/>

</dynamicvariables>

Example 2:

Code Block
titleAssigning a dynamic variable value from the output of a command execution
langxml
<dynamicvariables>

    <variable name="previous.java.version" checkonce="true"
              dir="${INSTALL_PATH}"
              executable="jre/bin/java" stderr="true"
              type="process" ignorefailure="true"
              condition="haveInstallPath+isUpgrade">
      <arg>-version</arg>
      <filters>
        <regex regexp="java version[^\d]+([\d\._]+)" select="\1"/>
      </filters>
    </variable>

</dynamicvariables>

Filtering Values

After straight evaluation, each dynamic variable value can be filtered using predefined filters. Each filter might have a number of attributes to configure its behavior.

Multiple nested filters can be used. In this case, the order of defining them is the order they will be executed at installation time.

Filters evaluated on each panel change, regardless whether <dynamicvariable checkonce="true"/>, because there can change several variables also resolved in filter attributes.

Filters are embedded in the nested filters element like this:

Code Block
titleDynamic Variable Filter Element Definition
languagehtml/xml
<dynamicvariable ...>
   ... <!-- other nested arguments might go here -->
   <filters>
      <filter1 .../>
      <filter2 .../>
      ... <!-- more filters might go here -->
   </filters>
</dynamicvariable>

 

Regular Expression Filter

After straight evaluation, each dynamic variable value can be filtered using a Java regular expression. This is done by the nested regex element.

Attributes:

  • regexp
    The Java regular expression to be used for selecting from the variable value or for replacing certain parts of the variable value. For more information see the Java Platform SE 6 API and other documents describing the according regular expression syntax more in detail.
  • select (one of both, select or replace must be given)
    Selection expression according to regexp, used to select certain groups from the expression defined in regexp and possibly combine them with several text around.
  • replace (one of both, select or replace must be given)
    Replacement expression according to regexp, used to replace the regular expression defined in regexp and possibly combine them with several text around.
  • defaultValue (optional)
    The default value to be used if the expression defined in regexp does not match the enclosing variable value at all.
  • casesensitive (optional, defaults to "true")
    Whether the regular expression matching should consider the case of alphabetic letters or not for matching.
  • global (optional, defaults to "false")
    Whether the replacement operation should be performed on the entire variable value, rather than just the first occurance. This has effect only on using together with replace.

Example:

Code Block
titleFiltering dynamic variable assignments using regular expressions
langxml
<dynamicvariables>

    <variable name="previous.version" jarfile="${INSTALL_PATH}/${INSTALL_SUBPATH}/libs/config.jar"
              entry="release.properties" type="options"
              key="release.version"
              checkonce="false" ignorefailure="true" condition="upgradecheck">
      <filters>
        <regex regexp="([0-9]+(\.[0-9]+){2})" select="\1" defaultvalue="none"/>
      </filters>
    </variable>

    <variable name="RegExTest.Select.Windows" checkonce="true"
              regkey="HKLM\\SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Environment"
              regvalue="Path">
      <filters>
        <regex regexp="([^;]*)(.*)"
               select="\1"
               defaultValue="(unmatched)"
               casesensitive="false"/>
      </filters>
    </variable>

    <variable name="RegExTest.ReplaceFirst.Windows" checkonce="true"
              regkey="HKLM\\SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Environment"
              regvalue="Path">
      <filters>
        <regex regexp="([^;]*)"
               replace="+++ \1 +++"
               defaultValue="(unmatched)"
               casesensitive="false"
               global="false"/>
      </filters>
    </variable>

    <variable name="RegExTest.ReplaceAll.Windows" checkonce="true"
              regkey="HKLM\\SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Environment"
              regvalue="Path">
      <filters>
        <regex regexp="([^;]*)"
               replace="+++ \1 +++"
               defaultValue="(unmatched)"
               casesensitive="false"
               global="true"/>
      </filters>
    </variable>

</dynamicvariables>

Location Filter

After straight evaluation, each dynamic variable value can be filtered to be canonicalized like a filename. This is done by the nested location element.

Attributes:

  • basedir
    The root directory relative path to be assumed when the origin value is not an absolute path. If not set, the current working directory is assumed as the base directory, instead.
Code Block
titleExample of the location filter
languagehtml/xml
 <variable name="previous.wrapper.java.command.canonical" value="${previous.wrapper.java.home.canonical}/bin/java"
              condition="haveInstallPath+isCompatibleUpgrade+haveWrapperJavaCmd+isSetCanonicalJavaHome">
      <filters>
        <location basedir="${INSTALL_PATH}"/>
      </filters>
 </variable>