# pattern

edit## pattern

edit- filtertype: pattern kind: ... value: ...

Empty values and commented lines will result in the default value, if any, being selected. If a setting is set, but not used by a given filtertype, it may generate an error.

This filtertype will iterate over the actionable list and match indices matching a given pattern. They will remain in, or be removed from the actionable list based on the value of exclude.

### Filter chaining

It is important to note that while filters can be chained, each is linked by an
implied logical **AND** operation. If you want to match from one of several
different patterns, as with a logical **OR** operation, you can do so with the
pattern filtertype using *regex* as the kind.

This example shows how to select multiple indices based on them beginning with
either `alpha-`

, `bravo-`

, or `charlie-`

:

filters: - filtertype: pattern kind: regex value: '^(alpha-|bravo-|charlie-).*$'

Explaining all of the different ways in which regular expressions can be used
is outside the scope of this document, but hopefully this gives you some idea
of how a regular expression pattern can be used when a logical **OR** is desired.

The different `kinds`

are described as follows:

## prefix

editTo match all indices starting with `logstash-`

:

- filtertype: pattern kind: prefix value: logstash-

To match all indices *except* those starting with `logstash-`

:

- filtertype: pattern kind: prefix value: logstash- exclude: True

## suffix

editTo match all indices ending with `-prod`

:

- filtertype: pattern kind: suffix value: -prod

To match all indices *except* those ending with `-prod`

:

- filtertype: pattern kind: suffix value: -prod exclude: True

## timestring

editNo age calculation takes place here. It is strictly a pattern match.

To match all indices with a Year.month.day pattern, like `index-2017.04.01`

:

- filtertype: pattern kind: timestring value: '%Y.%m.%d'

To match all indices *except* those with a Year.month.day pattern, like
`index-2017.04.01`

:

- filtertype: pattern kind: timestring value: '%Y.%m.%d' exclude: True

### A word about regular expression matching with timestrings

Timestrings are parsed from strftime patterns, like `%Y.%m.%d`

, into regular
expressions. For example, `%Y`

is 4 digits, so the regular expression for that
looks like `\d{4}`

, and `%m`

is 2 digits, so the regular expression is `\d{2}`

.

What this means is that a simple timestring to match year and month, `%Y.%m`

will result in a regular expression like this: `^.*\d{4}\.\d{2}.*$`

. This
pattern will match any 4 digits, followed by a period `.`

, followed by 2 digits,
occurring anywhere in the index name. This means it *will* match monthly
indices, like `index-2016.12`

, as well as daily indices, like
`index-2017.04.01`

, which may not be the intended behavior.

To compensate for this, when selecting indices matching a subset of another
pattern, use a second filter with `exclude`

set to `True`

- filtertype: pattern kind: timestring value: '%Y.%m' - filtertype: pattern kind: timestring value: '%Y.%m.%d' exclude: True

This will prevent the `%Y.%m`

pattern from matching the `%Y.%m`

part of the
daily indices.

**This applies whether using timestring as a mere pattern match, or as part of
date calculations.**

## regex

editThis `kind`

allows you to design a regular-expression to match
indices or snapshots:

To match all indices starting with `a-`

, `b-`

, or `c-`

:

- filtertype: pattern kind: regex value: '^a-|^b-|^c-'

To match all indices *except* those ending with `a-`

, `b-`

, or `c-`

:

- filtertype: pattern kind: regex value: '^a-|^b-|^c-' exclude: True