trap 'rm /tmp/temp-$$; exit' INT TERM
	Clear up temp files if the script is interrupted via C-c.

trap '' HUP
	Ignore HUP signal.
trap - HUP
	Remove the previous trap (make HUP signal terminate our process again).

USR1, USR2
	The 2 user-purpose signals.

precmd() { print About to show the prompt... }
	Executed before the prompt is printed.
	!!! Prefer this instead of prompt customization if possible !!!

periodic()
	... only after the $PERIOD seconds have elapsed ...

chpwd()
	... then the directory changes in the shell ...