Get or set clipboard — external library

Here are the links for downloading compiled dll files: 64-bit version and 32-bit version.

Example of using the library in InDesign (tested in CC 2018)

var libPath = "/E/Archive/_JavaScript/Photoshop/Libraries/BasicExternalObject/BasicExternalObject.dll";
var psEX = new ExternalObject("lib:" + libPath);

main();

function main() {
	$.writeln(psEX.getClipboard());
	$.writeln("-----------------------------");
	//Put data on clipboard
	psEX.setClipboard("This is put on the clipboard!");
	//Get data from clipboard
	$.writeln(psEX.getClipboard());
	//Clear clipboard
	psEX.clearClipboard();
}

Example of using it in Photoshop (I haven't tested it yet)

var libPath =SCRIPTS_FOLDER + "/BasicExternalObject.dll";
var  psEX = new ExternalObject("lib:" + libPath);
$.writeln(psEX.getClipboard());
$.writeln("-----------------------------");
//Put data on clipboard
psEX.setClipboard("This is put on the clipboard!");
//Get data from clipboard
$.writeln(psEX.getClipboard());
//Clear clipboard
psEX.clearClipboard();

Just another option for Windows users for get/set clipboard and a new version of system that returns the results is modified External Lib example in the bridge SDK Bridge Developer Center | Adobe Developer Connection — BasicExternalObject. (The code shown is a replacement for the "BasicExternalObject" example in the SDK.)

This modified code was written by Paul Riggott, shame to lose it:

#include "BasicExternalObject.h"  
    #include "SoSharedLibDefs.h"  
    #include   
    #include   
    #include   
    #include   
      
    #if defined (_WINDOWS)  
        #pragma warning(disable : 4996) // Turn off warning about deprecated strcpy on Win  
    #endif  
      
    /** 
    * \brief To allow string manipulation 
    */  
    using namespace std;  
      
    /** 
    * \brief Utility function to handle strings and memory clean up 
    * 
    * \param s - The referenced string 
    */  
    static char* getNewBuffer(string& s)  
    {  
        // Dynamically allocate memory buffer to hold the string   
        // to pass back to JavaScript  
        char* buff = new char[1+s.length()];  
          
        memset(buff, 0, s.length()+1);  
        strcpy(buff, s.c_str());  
      
        return buff;  
    }  
      
      
    extern "C" BASICEXTERNALOBJECT_API long systemCmd(TaggedData* argv, long argc, TaggedData* retval)  
    {  
        // The returned value type  
        retval->type = kTypeString;      
        // Accept 1 and only 1 argument  
        if(argc != 1)  
        {  
            return kESErrBadArgumentList;  
        }  
      
        // The argument must be a string  
        if(argv[0].type != kTypeString)  
        {  
            return kESErrBadArgumentList;  
        }  
      
    char*  cmd = (argv[0].data.string);   
        FILE* pipe = _popen(cmd, "r");  
        if (!pipe) retval->data.string = "";  
        char buffer[128];  
        std::string result = "";  
        while(!feof(pipe)) {  
            if(fgets(buffer, 128, pipe) != NULL)  
                result += buffer;  
        }  
        _pclose(pipe);  
        retval->data.string = getNewBuffer(result);  
        return kESErrOK;  
    }  
    extern "C" BASICEXTERNALOBJECT_API long getClipboard(TaggedData* argv, long argc, TaggedData* retval)  
    {  
        // The returned value type  
        retval->type = kTypeString;      
        HANDLE h;     
      if (!OpenClipboard(NULL)) return kESErrBadArgumentList;    
      h = GetClipboardData(CF_TEXT);  
      CloseClipboard();  
      if(h){  
      string text;  
        text = (char*)h;  
        if(text.length() < 1) return kESErrBadArgumentList;  
        retval->data.string = getNewBuffer(text);  
      }else{  
    retval->data.string = "";  
      }  
        return kESErrOK;  
    }  
    extern "C" BASICEXTERNALOBJECT_API long clearClipboard(TaggedData* argv, long argc, TaggedData* retval)  
    {  
        if (OpenClipboard(NULL)){  
            EmptyClipboard();  
            CloseClipboard();  
        }  
        return kESErrOK;  
    }  
    extern "C" BASICEXTERNALOBJECT_API long setClipboard(TaggedData* argv, long argc, TaggedData * retval)  
    {      
        // Accept 1 and only 1 argument  
        if(argc != 1)  
        {  
            return kESErrBadArgumentList;  
        }  
      
        // The argument must be a string  
        if(argv[0].type != kTypeString)  
        {  
            return kESErrBadArgumentList;  
        }  
      
    string source = (argv[0].data.string);   
    int len = source.length() +1;  
    source = source.c_str();  
    if(OpenClipboard(NULL))  
    {  
        HGLOBAL clipbuffer;  
        char * buffer;  
        EmptyClipboard();  
        clipbuffer = GlobalAlloc(GMEM_DDESHARE, len);  
        buffer = (char*)GlobalLock(clipbuffer);  

        strcpy(buffer, LPCSTR(source.c_str()));  
        GlobalUnlock(clipbuffer);  
        SetClipboardData(CF_TEXT,clipbuffer);  
        CloseClipboard();  
    }  
      
        return kESErrOK;  
    }  
    /** 
    * \brief Free any string memory which has been returned as function result. 
    * 
    * \param *p Pointer to the string 
    */  
    BASICEXTERNALOBJECT_API void ESFreeMem (void* p)  
    {   
        delete(char*)(p);  
    }  
      
    /** 
    * \brief Returns the version number of the library 
    * 
    * ExtendScript publishes this number as the version property of the object  
    * created by new ExternalObject. 
    */  
    BASICEXTERNALOBJECT_API long ESGetVersion()  
    {  
        return 0x1;  
    }  
      
    /** 
    * \brief Initialize the library and return function signatures. 
    * 
    * These signatures have no effect on the arguments that can be passed to the functions. 
    * They are used by JavaScript to cast the arguments, and to populate the 
    * reflection interface. 
    */  
    BASICEXTERNALOBJECT_API char* ESInitialize (const TaggedData ** argv, long argc)   
    {   
        return "makeArray,getAverage,appendString_s,myScript_a,acceptBoolean_b";  
    }  
      
    /** 
    * \brief Terminate the library. 
    * 
    * Does any necessary clean up that is needed. 
    */  
    BASICEXTERNALOBJECT_API void ESTerminate()  
    {  
          
    }  

The source is here. Thanks SuperMerlin for posting it.