With variables you can customize many aspects of install4j. They can be used in all text fields and text properties in the install4j IDE as well as from the install4j API. The general variable syntax is


where prefix denotes the variable type and is one of

Text fields in the install4j IDE where you can use variables have a  variable selector next to them. In the popup menu, you first choose a variable system from the available variable types. In text properties of an installer element or a form component, you can use compiler variables, installer variables and custom localization keys, but not launcher variables.

The variable selection dialog then shows all known variables of the selected variable type.

For both compiler and installer variables install4j offers a fixed set of "system variables" that are prefixed with "sys.". These variables are not writable and it is discouraged to use this prefix for your own variables.

Compiler variables

Compiler variables are written as


The value of a compiler variable is a string that is known and replaced at compile time. The installer runtime or the generated launchers do not see this variable, but just the value that was substituted at runtime. Compiler variables are defined on the "General Settings->Compiler Variables" step.

You can use compiler variables for various purposes. The most common usage of a compiler variable is the possibility to define a string in one place and use it in many other places. You can then change the string in one place instead of having to look up all of its usages.

An example of this use case is the pre-defined sys.version variable that contains the value of the text field where you enter the application version. Another usage for compiler variables is to override certain project settings on a per-media file basis. For example, if you want to include one directory in the distribution tree for Windows but another one for macOS, you can use a compiler variable for that directory and override it for each media file.

To quickly override multiple variables for a single media file, you can configure overridden values on the "Customize project defaults->Compiler variables" step of the media wizard.

Finally, compiler variables can be overridden from the command line compiler as well as from the Gradle, Maven and Ant plugins.

When you use a compiler variable in your project that is not a system variable, it must be defined in on the "General Settings->Compiler Variables" step. If an unknown variable is encountered, the build will fail. You can use other variables in the value of a variable. Recursive definitions are detected and lead to a failure of the build. It is not possible to define compiler variables with the name of a system variable.

install4j provides a number of system compiler variables:

You can access environment variables on the build machine with the syntax


where "environmentVariableName" is the name of an environment variable. This is resolved at build time and only works if no compiler variable with the same name is defined on the "General Settings->Compiler Variables" step.

Compiler variable values in the IDE cannot be multi-line strings. If you need to insert a variable with a multi-line string, you can use the text file reference syntax


where path/to/file is either an absolute file path or a path relative to the config file. All text areas that have an adjacent variable selector button offer the "Insert contents of text file" action in its popup menu. The file chooser has an option whether to use a relative or an absolute path in the variable expression.

In order to debug problems with compiler variables, you can switch on the extra verbose output flag in the Build step. All variable replacements will then be printed to the build console.

The file path can be a variable expression itself, like in


so you can override it for each media file or pass it as a parameter to a command line build.

Installer variables

Installer variables are written as


The value of an installer variable is an arbitrary object that is not known at compile time. Installer variables are replaced at runtime in the installer, the uninstaller and in custom installer applications. They can optionally be predefined in the install4j IDE like compiler variables, but this is not required.

Undefined installer variables come into existence the first time they are defined at runtime. However, it is an error to use an undefined variable. For example, if you use an installer variable in an action, you have to make sure that the installer variable is defined before the action is executed.

Installer variables are used to wire together actions, screens and form components at runtime. The user input in screens is saved to variables that can be used in the properties of actions. Furthermore, installer variables can be used in condition and validation expressions. Some examples are given in the help topic on form screens. In script properties, you retrieve variables by invoking


Variable values can be set with the installer API by invoking

context.setVariable("variableName", variableValue)

You can analyze the bindings of an installer variable on the "Installer Variables" tab of an installer application configuration. That tab will show you a list of bound variables together with all bindings.

In order to document and categorize bound installer variables, you can pre-define them and set descriptions that will be displayed in the installer variable selector in the install4j IDE.

A common scenario is the need to calculate a variable value at runtime with some custom code and use the result as the initial value of a form component. To achieve this, you can add a "Set a variable" action to the startup screen and set its "Variable name" property to some variable name. In this context, install4j expects a variable name and you must not use the ${installer:variableName} syntax but specify the plain variableName only. The return value of the "Script" property is written to the variable.

For example, if this variable represents the initial directory that is displayed for a "Directory chooser" form component, you set the "Initial Directory" property of that form component to ${installer:variableName}. In this way you have wired the results of an action with a behavior of a screen.

Another important use of installer variables is in the names of custom installation roots. In most cases, the name of a custom installation root contains an installer variable that is resolved at runtime. Often, one of the system installer variables that represent a "magic" folder can be used, such as ${installer:sys.system32Dir} for the Windows system32 directory.

When you use installer variables in properties that display text, such as the screen title or the label properties of form components, a live binding will be created and the displayed text is updated automatically when the variable values change.

Installer variables can be passed to the installer, uninstaller or custom installer applications from the command line prefixed with -V:

-VmyVar=test "-VmyVarWithSpaces=this is a test"

Alternatively, you can specify a property file containing installer variables with -varfile, where the file contains one variable definition per line. The variables that are created will be instances of java.lang.String.

install4j provides a number of system installer variables:

Launcher variables

Launcher variables are written as


The value of a launcher variable is a string that is not known at compile time. In contrast to installer variables, they are replaced by the launcher and not by Java code, so the replaced value is seen by the JVM at startup. Launcher variables can only be used in the "VM parameters" and "Arguments" text fields on the "Java invocation" step of the launcher wizard.

No user-defined launcher variables exist, the available system launcher variables are:

I18N messages

I18N messages are written as


The value of an I18N message depends on the language that is selected for the installer. You can use this facility to localize messages in your installers if they support multiple languages. To do that, you supply key-value pairs in the custom localization file. The variable selection dialog for I18N messages shows all system messages as well as all messages in the custom localization file for the principal language of your project.

All standard messages displayed by install4j can be referenced with this syntax as well. You can locate the key name in one of the message_*.utf8 files in the $INSTALL4J_HOME/resource/messages directory and use it anywhere in your project. The standard messages can be overwritten by your custom localization files.

Default values for missing variables

For the text field syntax of installer and compiler variables there is a mechanism to supply a default value in case the variable is not defined: After the variable name you add the delimiter ?: and insert the default value before the closing curly bracket.

For example:


will resolve to defaultValue if the installer variable "myVariable" is not defined. The default value can be another variable, also of a different type. For example:


If the installer variable "updatesUrl" is not defined, the compiler variable "sys.updatesUrl" is inserted. This is the default value of the "Update descriptor URL" property of the "Check for update" action.

The chain of default values can be arbitrarily long:

${installer:one?:${installer:two?:${installer:three?:${installer:four?:some plain text}}}}

This will resolve to the first defined installer variable out of "one", "two", "three", "four" or to some plain text if none of them are defined.

Binding variables to non-text properties

Many bean properties do not take text input, for example boolean, integer or enum properties, so that the variable syntax ${installer:myVariable} for text fields is not applicable. For these properties, you can select "Switch to text mode" in the context menu and enter a variable expression that resolves to the required type. Conversions from string values are important because compiler variables can only hold string values, unlike installer variables that can hold arbitrary types.

The help icon in the property editor tells you what the property type is and also informs about the supported conversions from other primitive types or strings. For example, "true" or "false" string values are supported for boolean properties as well, which is what you would use with a compiler variable. For enum properties, the name of the enum or the ordinal as a number or as a string will be resolved to the actual enum value. Also, numeric values will be parsed from strings.

If you develop a custom bean and want to support that functionality as well, you have to enable it in the property descriptor and insert a call into the property getter as explained in the Javadoc for AbstractBean.

Using variables in your own applications

Frequently there is a need in the installed applications to access user input that was made in the installer. The launcher API provides the helper class com.install4j.api.launcher.Variables to access the values of installer variables.

There are two ways that installer variables can be persisted in the installer: First, installer variables are saved to the default response file .install4j/response.varfile that is created when the installer exits or if a "Create response file" action is executed. Only response file variables are saved to that file. Secondly, selected installer variables can be saved to the Java preference store. com.install4j.api.launcher.Variables offers methods to load variables from both sources.

Saving to the Java preference store is interesting if you want to modify those variable values in your applications and save back the modified values. The Java preference store is available on a per-user basis so that it is possible to modify settings even if the user does not have write permissions for the installation directory. com.install4j.api.launcher.Variables has methods for loading and saving the entire map of installer variables that was saved in the installer. Also, it is possible to specify an arbitrary package to which the installer variables are saved, so that settings can be shared between different installers.

Finally, it is useful to access compiler variables in your own applications. For example, the version number configured in the install4j IDE can be accessed in your own application through com.install4j.api.launcher.Variables.