Modcheck

modcheck is a minimalist X11 utility that checks the current state of keyboard modifier keys. It queries the X server to determine which modifier keys (Super, Shift, Control, Alt) are currently pressed, either reporting all active modifiers or checking for a specific one via its exit status.

Download

• modcheck 1.0 (2025-10-11)

Features

• Real-time modifier detection - Queries X11 keyboard state directly
• Exit status checking - Returns 0/1 for scripting and automation
• Multiple modifier support - Detects Super, Shift, Control, and Alt keys
• Left/right key detection - Checks both left and right variants of each modifier
• Flexible output - Print all modifiers or check a specific one
• Lightweight - Single-file C program with minimal dependencies

Dependencies

Build time:

• C compiler (gcc or clang)
• make
• X11 headers

Runtime:

• X11

Installation

Edit config.mk to match your local setup (modcheck is installed into the /usr/local namespace by default), then simply enter the following command to install (if necessary as root):

make clean install

Usage

Check all currently pressed modifiers:

modcheck

Check if a specific modifier is pressed:

if modcheck super; then
    echo "Super key is pressed"
fi

Get source here.