Output filtering

When a project becomes bigger over time and includes a lot of Kubernetes objects, it may become required to operate on only a subset of them (e.g. apply only a part of an application).

Tanka helps you with this, by allowing you to limit the used objects on the command line using the --target flag. Say you are deploying an nginx instance with a special nginx.conf and want to apply the ConfigMap first:

# show the ConfigMap
tk show -t configmap/nginx .

# all good? apply!
tk apply -t configmap/nginx .

# and apply everything else:
tk apply .

The syntax of the --target / -t flag is --target=<kind>/<name>. If multiple objects match this pattern, all of them are used.

The --target / -t flag can be specified multiple times, to work with multiple objects.

Regular Expressions

The argument passed to the --target flag is interpreted as a RE2 regular expression.

This allows you to use all sorts of wildcards and other advanced matching functionality to select Kubernetes objects:

# show all deployments
tk show . -t 'deployment/.*'

# show all objects named "loki"
tk show . -t '.*/loki'

Gotchas

When using regular expressions, there are some things to watch out for:

Line Anchors

Tanka automatically surrounds your regular expression with line anchors:

^<your expression>$

For example, --target 'deployment/.*' becomes ^deployment/.*$.

Quoting

Regular expressions may consist of characters that have special meanings in shell. Always make sure to properly quote your regular expression using single quotes.

# shell attempts to match the wildcard itself:
zsh-5.4.2$ tk show . -t deployment/.*
zsh: no matches found: deployment/.*

# properly quoted:
zsh-5.4.2$ tk show . -t 'deployment/.*'
---
apiVersion: apps/v1
kind: Deployment
# ...

Excluding

Sometimes it may be desirably to exclude a single object, instead of including all others.

To do so, prepend the regular expression with an exclamation mark (!), like so:

# filter out all Deployments
tk show . -t '!deployment/.*'