Source Code Overview

This page describes application processes and source code.

Applications, Frameworks and Libraries

The application is written in C++17 and uses Qt framework.

Source code can be build either with CMake.

Most icons in the application are taken from theme by default (which currently works only on Linux) with fallback to built-in icons provided by FontAwesome.

The application logo and icons were created in Inkscape (icon source is in src/images/icon.svg).

Application Processes

There are these system processes related to CopyQ:

  • Main GUI application

  • Clipboard monitor - executes automatic clipboard commands

  • Menu command filter - enables/hides custom menu items based on “Filter” field in menu commands

  • Display command - executes display commands as needed

  • Clipboard and X11 selection owner and synchronization - provides clipboard data; launched as needed

  • Multiple clients - anything run by user from Action dialog or triggered as menu, automatic or global-shortcut command

Main GUI Application

The main GUI application (or server) can be executed by running copyq binary without attributes (session name can be optionally specified on command line).

It creates local server allowing communication with clipboard monitor process and other client processes.

Each user can run multiple main application processes each with unique session name (default name is empty).

Clipboard Monitor

Clipboard monitoring happens in separate process because otherwise it would block GUI (in Qt clipboard needs to be accessed in main GUI thread). The process is allowed to crash or loop indefinitely due to bugs on some platforms.

Setting and retrieving clipboard can still happen in GUI thread (copying and pasting in various GUI widgets) but it’s preferred to send and receive clipboard data using monitor process.

The monitor process is launched as soon as GUI application starts and is restarted whenever it doesn’t respond to keep-alive requests.

Clients and Scripting

Scripting language is Qt Script (mostly same syntax and functions as JavaScript).

API is described in Scripting API.

A script can be started by passing arguments to copyq. For example: copyq "1+1"

After script finishes, the server sends back output of last command and exit code (non-zero if script crashes).

copyq eval 'read(0,1,2)' # prints first three items in list
copyq eval 'fail()' # exit code will be non-zero

While script is running, it can send print requests to client.

copyq eval 'print("Hello, "); print("World!\n")'

Scripts can ask for stdin from client.

copyq eval 'var client_stdin = input()'

The script run in current directory of client process.

copyq eval 'Dir().absolutePath()'
copyq eval 'execute("ls", "-l").stdout'

Single function call where all arguments are numbers or strings can be executed by passing function name and function arguments on command line. Following commands are equal.

copyq eval 'copy("Hello, World!")'
copyq copy "Hello, World!"

Getting application version or help mustn’t require the server to be running.

copyq help
copyq version

Scripts run in separate thread and communicate with main thread by calling methods on an object of ScriptableProxy class. If called from non-main thread, these methods invoke a slot on an QObject in main thread and pass it a function object which simply calls the method again.

bool ScriptableProxy::loadTab(const QString &tabName)
    // This section is wrapped in an macro so to remove duplicate code.
    if (!m_inMainThread) {
        // Callable object just wraps the lambda so it's possible to send it to a slot.
        auto callable = createCallable([&]{ return loadTab(tabName); });

        m_inMainThread = true;
        QMetaObject::invokeMethod(m_wnd, "invoke", Qt::BlockingQueuedConnection, Q_ARG(Callable*, &callable));
        m_inMainThread = false;

        return callable.result();

    // Now it's possible to call method on an object in main thread.
    return m_wnd->loadTab(tabName);

Platform-dependent Code

Code for various platforms is stored in src/platform.

This leverages amount of #ifs and similar preprocessor directives in common code.

Each supported platform implements PlatformNativeInterface and platformNativeInterface().

The implementations can contain:

  • Creating Qt application objects

  • Clipboard handling (for clipboard monitor)

  • Focusing window and getting window titles

  • Getting system paths

  • Setting “autostart” option

  • Handling global shortcuts (note: this part is in qxt/)

For unsupported platforms there is simple implementation to get started.


Plugins are built as dynamic libraries which are loaded from runtime plugin directory (platform-dependent) after application start.

Code is stored in plugins.

Plugins implement interfaces from src/item/itemwidget.h.

To create new plugin just duplicate and rewrite an existing plugin. You can build the plugin with make {PLUGIN_NAME}.

Continuous Integration (CI)

The application binaries and packages are built and tested on multiple CI servers.

  • GitHub Actions
    • Builds packages for OS X.

    • Builds and runs tests for Linux binaries.

  • GitLab CI
    • Builds and runs tests for Ubuntu 16.04 binaries.

    • Screenshots are taken while GUI tests are running. These are available if a test fails.

  • AppVeyor
    • Builds installers and portable packages for Windows.

    • Provides downloads for recent commits.

    • Release build are based on gcc-compiled binaries (Visual Studio builds are also available).

  • OBS Linux Packages
    • Builds release packages for various Linux distributions.

  • Beta OBS Linux Packages
    • Builds beta and unstable packages for various Linux distributions.

  • Coveralls
    • Contains coverage report from tests run with GitHub Actions.