Signal-like events and TRAP

• The EXIT event (also "signal" 0) occurs upon exit from the current shell.

• The DEBUG event takes place before every simple command, for command, case command, select command, and before the first command in a function. See also the description of extdebug for the shopt built-in for details of its effect.

• The ERR event takes place for each simple command with a non-zero exit status, subject to these conditions: it is not executed if the failed command is part of a while, until, or if condition expression, or in a && or || list, or if the command’s return value is being inverted via !. See also errexit for details.

• The RETURN event occurs each time a shell function or a script executed with the . (that's a dot) or source built-in returns to its caller.