command-switch.md

switch — conditional processing

switch 'template with $fields' {
    case 'some-value' {
        <subcommands>
    }
    case ~regexp~ {
        <subcommands>
    }
    default {
        <subcommands>
    }
}

Subcommands of switch: case, default.

Subcommands of case/default: all commands are allowed.

case regexps are matched against the template provided as the argument to switch. First matching case wins: its subcommands receive the message. If there was no match, an optional default block receives the message. There can be multiple case blocks, but only one default, and it must be the last block in switch.

The template can be a literal, quoted string or a regexp.

If there is no default subcommand, switch behaves as if it has an empty default. Unmatched messages are just emitted out of the switch with no modifications.

switch can work as an if-statement:

switch $host { case ~.~ {} default {drop} }
to stdout; # Only prints messages with non-empty $host

Although from subcommand is permitted inside case/default, its use there is discouraged. Messages emitted inside case/default ignore conditions and are emitted out of switch.

If your regexp has named groups, those groups will be placed as fields into the message:

switch $program {
    case ~^nginx-(?<kind>access|error)$~ {
        # $kind now is either 'access' or 'error'
    }
}