How can I modify a variable? I mean, I have the Apple data and at some point, the values are divided by 7. I want to multiply this last part of the variable by seven to get a correct form of the data. Can I do it in gretl?
You need to access the command line reference and function reference for the Gretl package to find out more about this process.
However, as far as I know, for command line interpreters, you'll need the source code of the entire distribution to be able to modify something or use the available commands to obtain what you need.
And here is the official website: http://gretl.sourceforge.net/