How do I direct the installer to perform actions before installation starts?

You can direct the installer to perform actions before installation starts by using the <preInstallationActionList> section. For example, the following code will set a different installation directory depending on the platform the installer is running on.

<preInstallationActionList>
  <setInstallerVariable>
    <name>installdir</name>
    <value>${env(SYSTEMDRIVE)}/${product_shortname}</value>
    <ruleList>
      <compareText>
       <text>${platform_name}</text>
       <logic>equals</logic>
       <value>windows</value>
      </compareText>
    </ruleList>
  </setInstallerVariable>
  <setInstallerVariable>
    <name>installdir</name>
    <value>/usr/local/${product_shortname}</value>
    <ruleList>
      <compareText>
       <text>${platform_name}</text>
       <logic>equals</logic>
       <value>linux</value>
      </compareText>
    </ruleList>
  </setInstallerVariable>
</preInstallationActionList>