Wrapping the `CopyToClipboard[]` in a `UsingFrontEnd[]`  allows us to use it scripts: 



    #!/usr/bin/env wolframscript

    string = "Pshhhkkkkkrrrrkakingkakingkakingtshchchchchchchchchdingdingding";
    UsingFrontEnd[CopyToClipboard[string]];



If a FrontEnd is already running you may have to quit it, and then rerun this script