Custom delimiters

Jinja2’s {{ }} collides with Helm, Go text/template, GitHub Actions, Terraform’s ${}-adjacent tooling and plenty of other things you might want to scaffold. deckctl solves this by letting each template pick its own delimiters.

The defaults

Kind	Start	End
Variable	{{	}}
Block	{%	%}
Comment	{#	#}

Overriding them

deckctl.yaml

delimiters:
  variable_start: "[["
  variable_end: "]]"
  block_start: "[%"
  block_end: "%]"
  comment_start: "[#"
  comment_end: "#]"

You only need to set what you’re changing — anything omitted falls back to the default. Each pair must be both set or both empty; setting variable_start without variable_end fails validation.

Now a Helm chart renders safely:

# values.yaml.tmpl — rendered by deckctl using [[ ]]
replicaCount: [[ replicas ]]
image:
  repository: [[ image_repo ]]
  tag: "[[ image_tag ]]"

# templates/deployment.yaml.tmpl — Helm's own {{ }} passes straight through
apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ include "chart.fullname" . }}
spec:
  replicas: {{ .Values.replicaCount }}

The other option: don’t add a suffix

Delimiters only matter for files deckctl actually renders. A file with no template suffix is copied byte-for-byte, {{ }} and all:

helm-chart/
  deckctl.yaml
  Chart.yaml.tmpl                 ← rendered (needs variables)
  values.yaml.tmpl                ← rendered (needs variables)
  templates/deployment.yaml       ← copied verbatim, Helm syntax untouched
  templates/service.yaml          ← copied verbatim

This is usually the simpler answer for Helm: only the handful of files that genuinely need substitution get a suffix, and the chart templates stay as-is with no delimiter gymnastics.

Reach for custom delimiters when a single file needs both — deckctl substitution and literal {{ }} in the output.

Which delimiters to pick

Any string works, but a few conventions:

Delimiters	Good for
[[ ]] / [% %] / [# #]	Helm, Go templates, anything using {{ }}
<< >> / <% %>	ERB-ish contexts, or when [ is meaningful (JSON/HCL lists)
{{{ }}}	Mustache-adjacent contexts — but easy to misread; avoid

Pick something that cannot appear literally in the file type you’re generating.

Copier’s _envops

Copier templates express the same thing through _envops, and deckctl maps it one-to-one:

copier.yml

_envops:
  variable_start_string: "[["
  variable_end_string: "]]"
  block_start_string: "[%"
  block_end_string: "%]"
  comment_start_string: "[#"
  comment_end_string: "#]"

See Copier compatibility.

Verifying

--dry-run prints the rendered content of every file, which is the fastest way to confirm the delimiters do what you think:

deckctl template apply helm-chart /tmp/out --source local --dry-run