Small example on how to get some information from the registry...

InstallScript registry functions

#include "Ifx.h"

#define TITLE "RegDBSetKeyValueEx & RegDBGetKeyValueEx"

export prototype MyFunction(HWND);
function MyFunction(hMSI)
    STRING szKey, szNumName, szNumValue, svNumValue, szTitle, szMsg;
    NUMBER nType, nSize, nvType, nvSize;
begin
    szKey = "SOFTWARE\\Wow6432Node\\Company Ltd.\\COMPANY\\20144";
    szNumName  = "ExePath";
    szNumValue = "12345";
    nType      = REGDB_STRING;
    nSize      = -1;

    RegDBSetDefaultRoot(HKEY_LOCAL_MACHINE);

    if (RegDBGetKeyValueEx (szKey, szNumName, nvType, svNumValue, nvSize) < 0) then
        MessageBox ("RegDBGetKeyValueEx failed.", SEVERE);
    else
        szMsg = "%s has value: %s\n\nThis data is %d bytes.";
        SprintfBox (INFORMATION, TITLE, szMsg, szNumName, svNumValue, nvSize);
    endif;
    
    // MsiSetProperty(hMSI, "USERNAME", svName);
end;

#define KEY1  "SOFTWARE"
#define KEY2  "SOFTWARE\\Microsoft"
#define KEY3  "SOFTWARE\\Wow6432Node\\Company Ltd.\\COMPANY"
#define TITLE "RegDBQueryKey Example" 

export prototype QueryingForRegistryKeys(HWND);
function QueryingForRegistryKeys(hMSI)
    STRING szMsg, nvItem;
    NUMBER nReturn, nItem, nCount;
    LIST   listSubKeys, listNames;
begin
    listSubKeys  = ListCreate(STRINGLIST);
    listNames    = ListCreate(STRINGLIST);
    if ((listNames = LIST_NULL) || (listSubKeys  = LIST_NULL)) then
        MessageBox ("Unable to create necessary lists.", SEVERE);
        abort;
    endif;

    RegDBSetDefaultRoot(HKEY_LOCAL_MACHINE);
    nReturn = RegDBQueryKey(KEY3, REGDB_KEYS, listSubKeys);
    if (nReturn < 0) then
        MessageBox("First call to RegDBQueryKey failed.", SEVERE);
    else
        szMsg = "Subkeys under " + KEY3 + " key:";
        SdShowInfoList(TITLE, szMsg, listSubKeys);
    endif;

    nReturn  = RegDBQueryKey(KEY2, REGDB_NAMES, listNames);
    if (nReturn < 0) then
        MessageBox("Second call to RegDBQueryKey failed.", SEVERE);
    else
        szMsg = "Named values under " + KEY2 + " key";
        SdShowInfoList(TITLE, szMsg, listNames);
    endif;
    
    nReturn = ListGetFirstString(listSubKeys, nvItem);
    while (nReturn != END_OF_LIST)
        SprintfBox (INFORMATION, TITLE, "%s", nvItem);
        nReturn = ListGetNextString (listSubKeys, nvItem);
    endwhile;

    ListDestroy (listNames);
    ListDestroy (listSubKeys);
    
    
    // how to disable a feature in Basic MSI projects - from InstallScript
    MsiSetFeatureState(hMSI, "GitIgnore", INSTALLSTATE_ABSENT);
    // must be called from:
    // Custom Actions -> Sequence -> Install UI Sequence -> After MigrateFeatureStates
    
    
    MsiSetTargetPath(hMSI, "MYDIRECTORY", customInstallationPath);
    // this works only if you add a new directory from: "Application Data" -> "Files and Folders"
    // don't forget to set the DIRECTORY IDENTIFIER to "MYDIRECTORY" (see the function call above)
    // right click on directory name and select properties to get to the DIRECTORY IDENTIFIER
end;

Hi Igor! Excuse me please, I am junior at InstallScript and I am trying to read a XML file from InstallScript but I can't. Suddenly, Do you know how to do this? Thank you!