Actual Installer Help \ Tricks with Variables
When using custsom variables on the System \ Variables page and it fails to retrieve the value (eg. Registry key or value does not exist) you can show some message to user or terminate the installation process.
To show a message, in the Default Data field type: MSG(your message)
To terminate the installation, in the Default Data field type: HALT(your message)
Function to extract directory from a file path: GETDIRX[path]
Case sensitive. Examples:
GETDIRX[C:\Folder\File.exe] returns C:\Folder
GETDIRX[<SetupExe>] returns a directory where the setup file is located