Basic format for command 'assign':
    vitis-sl copy [-e] <expression> -d <destination> [[--yes][--no]]

The command is intended for copying files (from the result
of the expression evaluation) to the specified directory.

For the format of the expression, see the help for the 'show' command:
    vitis-sl show --help

When one of the copied files and one of the files in the destination directory
have the same name, the user resolves this conflict interactively.
Optional flags --yes and --no disable interactivity.
If --yes is used, old files are replaced with new ones.
If --no is used, the conflicting files are skipped.

Examples:

    vitis-sl copy Books -d .
    This command copies files of the 'Books' category to the current directory.

    vitis-sl copy C++ i: Qt -d /home/user/Documents
    This command copies files those have both 'C++' category and 'Qt' category
    to the 'home/user/Documents'.