Gomplate

Flanksource Gomplate is a fork of hairyhenderson/gomplate that provides a unified templating library supporting multiple expression languages.

Features

• Go Text/Template – Full Go text/template support with an extended function library from gomplate (base64, collections, crypto, data formats, filepath, math, random, regexp, strings, time, and more)
• CEL (Common Expression Language) – CEL support with:
  • Standard CEL operators and built-ins
  • celext extensions (strings, encoders, lists, math, sets)
  • Kubernetes-specific helpers (k8s.*)
  • AWS helpers (aws.*)
  • Many gomplate functions remapped into CEL (base64, math, random, regexp, filepath, crypto, sets, etc.)
  • Optional-type support (obj.?field.orValue("default"))
• JavaScript (otto) – Lightweight JS evaluation via otto
• Struct templating – Walk Go structs/maps and apply templates to string fields in-place

Quick Reference

Language	Example	Documentation
Go Template	{{ .name | strings.ToUpper }}	GO_TEMPLATE.md
CEL	name.upperAscii()	CEL.md

CEL Quick Reference

# Arithmetic
2 + 3 // 5
"hello" + " world" // "hello world"
[1,2] + [3,4] // [1,2,3,4]
# Comparison / Logic
x > 5 && y != null
true ? "yes" : "no"
# String methods
"hello world".upperAscii() // "HELLO WORLD"
"hello world".split(" ") // ["hello", "world"]
"hello".startsWith("he") // true
"hello world".contains("world") // true
# Collections
[1,2,3].filter(e, e > 1) // [2, 3]
[1,2,3].map(e, e * 2) // [2, 4, 6]
[1,2,3].all(e, e > 0) // true
{"a":1,"b":2}.keys() // ["a","b"]
# Optional / null-safety
obj.?field.orValue("default")
obj.?a.?b.orValue("fallback")
# Kubernetes
k8s.isHealthy(pod)
k8s.cpuAsMillicores("500m") // 500
k8s.memoryAsBytes("1Gi")
# Math
math.Add([1,2,3]) // 6
math.greatest([1,2,3]) // 3
# Time
time.Now()
time.Since(timestamp("2023-01-01T00:00:00Z"))

See CEL.md for full reference.

Go Template Quick Reference

# Variables and output
{{ .name }}
{{ $x := "hello" }}{{ $x | strings.ToUpper }}
# Control flow
{{ if eq .status "ok" }}OK{{ else }}FAIL{{ end }}
{{ range .items }}{{ . }}{{ end }}
# String functions
{{ "hello world" | strings.ToUpper }} // HELLO WORLD
{{ "hello world" | strings.Split " " }} // [hello world]
{{ "hello" | strings.Repeat 3 }} // hellohellohello
# Data
{{ '{"key":"val"}' | json }} // map access
{{ .obj | toJSON }}
{{ .obj | toYAML }}
# Collections
{{ coll.Dict "a" 1 "b" 2 | toJSON }} // {"a":1,"b":2}
{{ slice 1 2 3 | coll.Reverse | toJSON }} // [3,2,1]
{{ coll.Sort (slice "b" "a" "c") | toJSON }} // ["a","b","c"]
# Math
{{ math.Add 1 2 3 }} // 6
{{ math.Max 1 5 3 }} // 5
# base64
{{ base64.Encode "hello" }} // aGVsbG8=
{{ "aGVsbG8=" | base64.Decode }} // hello
# Crypto
{{ crypto.SHA256 "hello" }}
# Delimiters (change if conflict with Helm)
# gotemplate: left-delim=$[[ right-delim=]]
$[[ .name ]]

See GO_TEMPLATE.md for full reference.

Installation

import"github.com/flanksource/gomplate/v3"

Usage

Go Template

result, err:=gomplate.RunTemplate(map[string]any{
"name": "world",
}, gomplate.Template{
Template: `Hello, {{ .name }}!`,
})

CEL

result, err:=gomplate.RunTemplate(map[string]any{
"name": "world",
}, gomplate.Template{
Expression: `"Hello, " + name + "!"`,
})

Struct Templating

typeConfigstruct {
MessagestringCountint
}
cfg:=Config{Message: "Hello, {{ .name }}!"}
err:=gomplate.Walk(map[string]any{"name": "world"}, &cfg)
// cfg.Message == "Hello, world!"
## CELevalhelperAsmallhelpercommandisavailableat `cmd/ceval` to evaluate CEL expressions against an input YAML or JSON file.Run it with:```bash
go run ./cmd/ceval -f env.yaml -e "labels['a/b/c']"

Example input file:

labels:
a/b/c: d

Output:

d