xbindkeys is a program that associates keys or mouse buttons to shell commands under X. After a little configuration, it can start many commands with the keyboard (e.g. control+alt+x starts an xterm) or with the mouse buttons.
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A 'Release' modifier was added to catch release events of keys or mouse buttons instead of press events. Xbindkeys doesn't use pthreads+system any more to start commands, it use fork+exec instead. Some modifications were made to make the code cleaner.