signal - dynamically loadable signal handling for Tcl/Tk

       Michael Schwartz <mschwart@nyx.net>. Tilman Kranz <tilde@tk-sls.de> patched this for wider portability on
       Linux

Tcl Signal Extension                               1.4.0.1 Tcl                                      signal(3tcl)

addsignoproc[-async]
       Adds a signal handler for signal signo through proc proc.  Signals can be provided by number, or the most
       common ones are provided by name (e.g., SIGHUP).  The proc is any Tcl procedure, and it is evaluated when
       the signal comes in.  It will be provided no arguments.

       Signal handlers have Posix semantics - they persist until reset.

       If -async is used, the signal handler is created using Tcl_AsyncCreate().  Checks for the signal are very
       frequent (each evaluation) using this technique, but one doesn't know quite where evaluation is or how to
       handle errors in this situation. The code will evaluate the provided procedure in the current interpreter
       if  available,  and  in the interpreter which added the signal handler otherwise. At least until a better
       scheme is suggested.

       The -async is especially useful to interrupt "runaway" procs, or to  cause  a  quick  exit;  the  default
       mechanism simply waits for another MainLoop cycle.

   signaldeletesigno
       Restores handling of signal signo to the default ( SIG_DFL ).

   signalprint
       Prints the handling of all signals with handlers. Formatted as
        signal ----> procedure or as
        signal !---> procedure

       if the signal is handled asynchronously

   signalprintsigno
       Prints the procedure for handling signal signo.  Prints the word UNHANDLED if no signal handler is active
       for that signal.

   signalversion
       Returns the string representing the current version of the package

       signal - dynamically loadable signal handling for Tcl/Tk

signal(add|delete|print|version)[options]