I would like to wrap a data file (~1MB) to golang app and then use that data in os.exec. The app runs on Linux.
How to define the data in the app, as a string or []byte, variable, or Const?
Should be defined in a global scope, or wrapped in a func?
How to pass the data from the app memory to the executed process ?
For building the data file(s) in to your program, you have a number of choices. You are correct in that you could manually copy/paste the data file(s) in to the program as types string, []byte as variables, but there are other packages/applications for go that handle this for you already that can also minimize your app's memory footprint. One example that comes to mind is go-bindata (link to repo) which does just this.
As for using the file in os/exec, I'm assuming you're trying to either pass the entire file to the program using either a file path or a raw string. For file paths, you would have to write the entire file to disk first. If you're trying to pass the entire file contents as a raw string, you can still use go-bindata or a string of the data file as arg in os/exec.Command.
P.S. - go-bindata has not seen updates in a while, so I would encourage you to seek more active forks or alternatives if you're having trouble using it.