Open a terminal. Run the following command to make sure you have the packages curl and libreoffice-calc installed:
apt-get install curl libreoffice-calc
Then you can use CURL to convert the GBK file to CSV. You have to replace example.gbk with the file you want to convert.
curl -F firstname.lastname@example.org https://www.rebasedata.com/api/v1/convert?outputFormat=csv -o output.zip
Now try to open the file output.zip. It will contain CSV files. You can open these CSV files with LibreOffice Calc. Make sure you specify "comma" as column separator.
If you cannot open the file output.zip, there was probably an error and the file contains the error message. Open it with gedit to see the error.
That's it! You successfully read your Firebird GBK backup file file.
The RebaseData PHP-Client internally uses our API to convert the Firebird GBK backup file file to a standardized format. Then you can read the data using PHP as shown above.