# Template Basics and Built-in Objects — Helm

Source: https://www.skillbyai.com/en/helm/t-basics

> Use Go template actions, built-in objects and common functions safely.

## Go templates plus Sprig

Helm templates use Go's `text/template` language plus the **Sprig** function library and some Helm-specific functions. Everything between `{{` and `}}` is an action. Built-in objects give you context: **`.Values`** (merged values), **`.Release`** (`.Release.Name`, `.Release.Namespace`, `.Release.IsUpgrade`, `.Release.Revision`), **`.Chart`** (fields of `Chart.yaml`, such as `.Chart.Name` and `.Chart.AppVersion`), **`.Capabilities`** (Kubernetes version and available API versions), **`.Template`** and **`.Files`** (access to non-template files in the chart). Functions are called with arguments or through **pipelines**: `{{ .Values.env | default "dev" | quote }}`. Useful ones: `default`, `quote`, `required` (fail with a message if a value is missing), `upper`, `trim`, `b64enc`, `toYaml`, `indent`/`nindent`. **Whitespace control** with `{{-` and `-}}` trims spaces and newlines on that side, which is how you keep the output valid YAML.

## From template to manifest

The template engine combines templates with values and built-in objects to produce plain YAML.

![A template page with gaps and a values card flowing into a gear, which outputs a complete page with the gaps filled in.](assets/figures/helm/section-4-map.svg) — Figure 4.1 — Rendering combines templates, values and built-in objects.

## Common patterns in one ConfigMap

`required` turns a missing value into a clear install-time error instead of a broken pod.

```yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-config
  namespace: {{ .Release.Namespace }}
data:
  APP_ENV: {{ .Values.env | default "dev" | quote }}
  API_URL: {{ required "apiUrl is required, e.g. --set apiUrl=https://..." .Values.apiUrl | quote }}
  LOG_LEVEL: {{ .Values.logLevel | default "info" | upper | quote }}
  RELEASE_INFO: "{{ .Chart.Name }}-{{ .Chart.Version }} rev {{ .Release.Revision }}"
```

## Quote strings that look like other types

YAML turns `true`, `yes`, `on`, `1.10` and `0123` into booleans or numbers. Environment variables and annotation values must be strings, so pipe them through `quote`. A version `1.10` without quotes becomes the number 1.1.

**Quiz:** What does `{{-` (with a dash) do?

- [ ] Subtracts one from a value
- [ ] Comments out the line
- [x] Trims whitespace and newlines to the left of the action
- [ ] Marks the value as required

*Answer:* Trims whitespace and newlines to the left of the action. The dash trims whitespace on that side of the action, keeping rendered YAML tidy.