https://docs.oracle.com/cd/E88353_01/html/E37842/tk--fileevent-3.html
Tk::fileevent - man pages section 3: Library Interfaces and Headers
Tk::fileevent - Execute a callback when a filehandle becomes readable or writable
man pagestksectionlibraryinterfaces
https://manpages.ubuntu.com/manpages/xenial/man3/Tk::fileevent.3pm.html
Ubuntu Manpage: Tk::fileevent - Execute a callback when a filehandle becomes readable or writable
Execute a callback when a filehandle becomes readable or writable