you can also adapt this one liner
    
    command -range TmuxSession execute "!tmux.session " . @*

or if you do need multiline visual selection change `@*` to `substitute(@*,"\n"," ","g")`

The `@*` register stores current selection (for linux, on windows there could be different naming convention).

The `-range` is only to avoid an error if you want to execute this command with range marks, i.e. `'<,'>TmuxSession`.