17. Explorer

17.1. Description

Explorers are small shell scripts, which will be executed on the target host. The aim of each explorer is to give hints to types on how to act on the target system. An explorer outputs the result to stdout, which is usually a one liner, but may be empty or multi line especially in the case of type explorers.

There are general explorers, which are run in an early stage, and type explorers. Both work almost exactly the same way, with the difference that the values of the general explorers are stored in a general location and the type specific below the object.

Explorers can reuse other explorers on the target system by calling

$__explorer/<explorer_name> (general and type explorer)

or

$__type_explorer/<explorer name> (type explorer).

In case of significant errors, the explorer may exit non-zero and return an error message on stderr, which will cause cdist to abort.

You can also use stderr for debugging purposes while developing a new explorer.

17.2. Examples

A very simple explorer may look like this:

hostname

Which is in practise the hostname explorer.

A type explorer, which could check for the status of a package may look like this:

if [ -f "$__object/parameter/name" ]; then
   name="$(cat "$__object/parameter/name")"
else
   name="$__object_id"
fi

# Expect dpkg failing, if package is not known / installed
dpkg -s "$name" 2>/dev/null || exit 0