GNU Rush
	Restricted User Shell	Sergey Poznyakoff

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4.4.7 Fall-through

The fall-through statement is a special action that does not execute the requested command. When a matching fall-through rule is encountered, rush evaluates it and continues scanning its configuration for the next matching rule. Any modifications to the request found in the fall-through rule take effect immediately, which means that subsequent rules will see modified command line and environment. Execution of any other actions found in the fall-through rule is delayed until a usual rule is found.

A fall-through rule is declared using the following statement:

rule: fall-through

rule: fallthrough

Declare a fall-through rule.

Usually this statement is placed as the last statement in a rule, e.g.:

rule default
  umask 002
  clrenv
  keepenv HOME USERNAME PATH
  fall-through

Fall-through rules provide a way to set default values for subsequent rules. For example, any rules that follow the ‘default’ rule shown above, will inherit the umask and environment set there.

One can also use fall-through rules to “normalize” command lines. For example, consider this rule:

rule default
  set [0] =~ "s|.*/||"
  fall-through

It will remove all path components from the first command line argument. As a result, all subsequent rules may expect a bare binary name as the first argument.

Yet another common use for such rules is to enable accounting (see the next subsection), or set resource limits for the rest of rules:

rule default
  limit l1
  fall-through