functions.md

Template Functions Reference

render provides 80+ template functions in addition to Go's built-in functions.

Casing Functions

Transform string case.

Function	Description	Example
lower	Lowercase	{{ "Hello" | lower }} → hello
upper	Uppercase	{{ "Hello" | upper }} → HELLO
title	Title Case	{{ "hello world" | title }} → Hello World
camelCase	camelCase	{{ "hello world" | camelCase }} → helloWorld
pascalCase	PascalCase	{{ "hello world" | pascalCase }} → HelloWorld
snakeCase	snake_case	{{ "HelloWorld" | snakeCase }} → hello_world
kebabCase	kebab-case	{{ "HelloWorld" | kebabCase }} → hello-world
upperSnakeCase	UPPER_SNAKE	{{ "helloWorld" | upperSnakeCase }} → HELLO_WORLD
upperKebabCase	UPPER-KEBAB	{{ "helloWorld" | upperKebabCase }} → HELLO-WORLD

Trimming Functions

Remove characters from strings.

Function	Signature	Description
trim	trim s	Remove leading/trailing whitespace
trimPrefix	trimPrefix prefix s	Remove prefix
trimSuffix	trimSuffix suffix s	Remove suffix
trimLeft	trimLeft cutset s	Remove leading chars in cutset
trimRight	trimRight cutset s	Remove trailing chars in cutset
trimChars	trimChars cutset s	Remove leading and trailing chars in cutset

Examples:

{{ "  hello  " | trim }}                    → "hello"
{{ "hello.txt" | trimSuffix ".txt" }}       → "hello"
{{ "###hello###" | trimChars "#" }}         → "hello"

String Manipulation

Function	Signature	Description
replace	replace old new s	Replace all occurrences
replaceN	replaceN old new n s	Replace first n occurrences
contains	contains substr s	Check if contains substring
hasPrefix	hasPrefix prefix s	Check prefix
hasSuffix	hasSuffix suffix s	Check suffix
repeat	repeat s n	Repeat string n times
reverse	reverse s	Reverse string
substr	substr s start end	Substring (supports negative indices)
truncate	truncate s length	Truncate to length
padLeft	padLeft s length pad	Pad left to length
padRight	padRight s length pad	Pad right to length
center	center s length pad	Center with padding
wrap	wrap s width	Word wrap at width
indent	indent spaces s	Indent with spaces
nindent	nindent spaces s	Newline + indent

Examples:

{{ "hello" | replace "l" "L" }}             → "heLLo"
{{ "hello" | substr 0 3 }}                  → "hel"
{{ "hi" | padLeft 5 "0" }}                  → "000hi"
{{ "yaml:\n  key: value" | indent 2 }}      → "  yaml:\n    key: value"

Splitting and Joining

Function	Signature	Description
split	split sep s	Split string by separator
splitN	splitN sep n s	Split into at most n parts
join	join sep items	Join array with separator
lines	lines s	Split into lines
first	first items	First element
last	last items	Last element
rest	rest items	All but first
initial	initial items	All but last
nth	nth n items	Nth element (0-indexed)

Examples:

{{ "a,b,c" | split "," }}                   → ["a", "b", "c"]
{{ list "a" "b" "c" | join "-" }}           → "a-b-c"
{{ list 1 2 3 | first }}                    → 1
{{ list 1 2 3 | rest }}                     → [2, 3]

Concatenation

Function	Signature	Description
concat	concat items...	Concatenate strings
cat	cat items...	Concatenate with spaces

Examples:

{{ concat "hello" "world" }}                → "helloworld"
{{ cat "hello" "world" }}                   → "hello world"

Conversion Functions

Function	Signature	Description
toString	toString v	Convert to string
toInt	toInt v	Convert to int
toInt64	toInt64 v	Convert to int64
toFloat	toFloat v	Convert to float64
toBool	toBool v	Convert to bool
toJson	toJson v	Convert to JSON string
toPrettyJson	toPrettyJson v	Convert to pretty JSON
fromJson	fromJson s	Parse JSON string

Examples:

{{ 42 | toString }}                         → "42"
{{ "123" | toInt }}                         → 123
{{ .config | toJson }}                      → '{"key":"value"}'
{{ .config | toPrettyJson }}                → formatted JSON

Unicode Functions

Function	Signature	Description
nfc	nfc s	NFC normalization
nfd	nfd s	NFD normalization
nfkc	nfkc s	NFKC normalization
nfkd	nfkd s	NFKD normalization
ascii	ascii s	Convert to ASCII
slug	slug s	URL-safe slug

Examples:

{{ "café" | ascii }}                        → "cafe"
{{ "Hello World!" | slug }}                 → "hello-world"

Formatting

Function	Signature	Description
quote	quote s	Double-quote string
squote	squote s	Single-quote string
printf	printf format args...	Formatted string

Examples:

{{ "hello" | quote }}                       → '"hello"'
{{ printf "%s-%d" "item" 42 }}              → "item-42"

Comparison and Logic

Function	Signature	Description
eq	eq a b	Equal (deep comparison)
ne	ne a b	Not equal
lt	lt a b	Less than
le	le a b	Less than or equal
gt	gt a b	Greater than
ge	ge a b	Greater than or equal
and	and a b	Boolean AND
or	or a b	Boolean OR
not	not a	Boolean NOT
default	default def val	Default if empty
empty	empty v	Check if empty
coalesce	coalesce items...	First non-empty
ternary	ternary cond true false	Conditional value

Examples:

{{ if eq .status "active" }}active{{ end }}
{{ .name | default "Anonymous" }}
{{ .value | empty }}                        → true/false
{{ ternary .enabled "on" "off" }}

Collection Functions

Function	Signature	Description
list	list items...	Create a list
dict	dict pairs...	Create a dictionary
keys	keys m	Get map keys
values	values m	Get map values
hasKey	hasKey m key	Check if key exists
get	get m key	Get value by key
set	set m key val	Set value (returns new map)
unset	unset m key	Remove key (returns new map)
merge	merge maps...	Merge maps
append	append items val	Append to list
prepend	prepend items val	Prepend to list
uniq	uniq items	Remove duplicates
sortAlpha	sortAlpha items	Sort alphabetically
len	len items	Length

Examples:

{{ list 1 2 3 }}                            → [1, 2, 3]
{{ dict "a" 1 "b" 2 }}                      → {"a": 1, "b": 2}
{{ .config | keys }}                        → list of keys
{{ hasKey .config "debug" }}                → true/false
{{ .items | sortAlpha }}                    → sorted list

Math Functions

Function	Signature	Description
add	add a b	Addition
sub	sub a b	Subtraction
mul	mul a b	Multiplication
div	div a b	Division
mod	mod a b	Modulo
max	max items...	Maximum
min	min items...	Minimum
floor	floor v	Floor
ceil	ceil v	Ceiling
round	round v	Round

Examples:

{{ add 1 2 }}                               → 3
{{ mul 3 4 }}                               → 12
{{ div 10 3 }}                              → 3
{{ max 1 5 3 }}                             → 5
{{ 3.7 | floor }}                           → 3

Regex Functions

Function	Signature	Description
regexMatch	regexMatch pattern s	Check if matches
regexFind	regexFind pattern s	Find first match
regexFindAll	regexFindAll pattern s n	Find all matches
regexReplace	regexReplace pattern repl s	Replace matches
regexSplit	regexSplit pattern s n	Split by pattern

Examples:

{{ regexMatch "^[a-z]+$" "hello" }}         → true
{{ regexFind "[0-9]+" "abc123def" }}        → "123"
{{ regexReplace "[0-9]" "X" "a1b2c3" }}     → "aXbXcX"

Counting Functions

Function	Signature	Description
count	count substr s	Count occurrences
countWords	countWords s	Count words
countLines	countLines s	Count lines

Examples:

{{ "hello" | count "l" }}                   → 2
{{ "hello world" | countWords }}            → 2
{{ "a\nb\nc" | countLines }}                → 3

Pipeline Usage

Functions can be chained using pipes:

{{ .name | lower | replace " " "_" | truncate 20 }}
{{ .items | sortAlpha | join ", " }}
{{ .config | toPrettyJson | indent 2 }}

Error Handling

Some functions return errors for invalid input:

{{ div 10 0 }}                              → error: division by zero
{{ "abc" | toInt }}                         → error: cannot convert "abc" to int
{{ regexMatch "[invalid" "test" }}          → error: invalid regex pattern

Use conditionals or default to handle potential errors:

{{ if .value }}{{ .value | toInt }}{{ else }}0{{ end }}