Sprig: Template functions for Go templates

The Go language comes with a built-in template language, but not very many template functions. This library provides a group of commonly used template functions.

It is inspired by the template functions found in Twig.

Usage

API documentation is available at GoDoc.org, but read on for standard usage.

Load the Sprig library

To load the Sprig FuncMap:

import (
  "github.com/Masterminds/sprig"
  "html/template"
)

// This example illustrates that the FuncMap *must* be set before the
// templates themselves are loaded.
tpl := template.Must(
  template.New("base").Funcs(sprig.FuncMap()).ParseGlob("*.html")
)

Call the functions inside of templates

By convention, all functions are lowercase. This seems to follow the Go idiom for template functions (as opposed to template methods, which are TitleCase).

Example:

{{ "hello!" | upper | repeat 5 }}

Produces:

HELLO!HELLO!HELLO!HELLO!HELLO!

Functions

Date Functions

• date: Format a date, where a date is an integer type or a time.Time type, and format is a time.Format formatting string.
• dateModify: Given a date, modify it with a duration: date_modify "-1.5h" now. If the duration doesn't parse, it returns the time unaltered. See time.ParseDuration for info on duration strings.
• now: Current time.Time, for feeding into date-related functions.
• htmlDate: Format a date for use in the value field of an HTML "date" form element.
• dateInZone: Like date, but takes three arguments: format, timestamp, timezone.
• htmlDateInZone: Like htmlDate, but takes two arguments: timestamp, timezone.

String Functions

• trim: strings.TrimSpace
• trimAll: strings.Trim, but with the argument order reversed trimAll "$" "$5.00" or "$5.00 | trimAll "$"
• trimSuffix: strings.TrimSuffix, but with the argument order reversed trimSuffix "-" "5-"
• trimPrefix: strings.TrimPrefix, but with the argument order reversed trimPrefix "$" "$5"
• upper: strings.ToUpper
• lower: strings.ToLower
• title: strings.Title
• repeat: strings.Repeat, but with the arguments switched: repeat count str. (This simplifies common pipelines)
• substr: Given string, start, and length, return a substr.
• nospace: Remove all spaces from a string. h e l l o becomes hello.
• abbrev: Truncate a string with ellipses
• trunc: Truncate a string (no suffix). trunc 5 "Hello World" yields "hello".
• abbrevboth: Truncate both sides of a string with ellipses
• untitle: Remove title case
• intials: Given multiple words, return the first letter of each word
• randAlphaNum: Generate a random alpha-numeric string
• randAlpha: Generate a random alphabetic string
• randAscii: Generate a random ASCII string, including symbols
• randNumeric: Generate a random numeric string
• wrap: Wrap text at the given column count
• wrapWith: Wrap text at the given column count, and with the given string for a line terminator: wrap 50 "\n\t" $string
• contains: strings.Contains, but with the arguments switched: contains "cat" "uncatch". (This simplifies common pipelines)
• hasPrefix: strings.hasPrefix, but with the arguments switched: hasPrefix "cat" "catch".
• hasSuffix: strings.hasSuffix, but with the arguments switched: hasSuffix "cat" "ducat".
• quote: Wrap strings in double quotes. quote "a" "b" returns "a" "b"
• squote: Wrap strings in single quotes.
• cat: Concatenate strings, separating them by spaces. cat $a $b $c.
• indent: Indent a string using space characters. indent 4 "foo\nbar" produces " foo\n bar"
• replace: Replace an old with a new in a string: $name | replace " " "-"
• plural: Choose singular or plural based on length: len $fish | plural "one anchovy" "many anchovies"
• uuidv4: Generate a UUID v4 string
• sha256sum: Generate a hex encoded sha256 hash of the input
• toString: Convert something to a string

String Slice Functions:

• join: strings.Join, but as join SEP SLICE
• split: strings.Split, but as split SEP STRING. The results are returned as a map with the indexes set to _N, where N is an integer starting from 0. Use it like this: {{$v := "foo/bar/baz" | split "/"}}{{$v._0}} (Prints foo)
• splitList: strings.Split, but as split SEP STRING. The results are returned as an array.
• toStrings: convert a list to a list of strings. 'list 1 2 3 | toStrings' produces '["1" "2" "3"]'
• sortAlpha: sort a list lexicographically.

Integer Slice Functions:

• until: Given an integer, returns a slice of counting integers from 0 to one less than the given integer: range $i, $e := until 5
• untilStep: Given start, stop, and step, return an integer slice starting at 'start', stopping at stop, and incrementing by 'step'. This is the same as Python's long-form of 'range'.

Conversions:

• atoi: Convert a string to an integer. 0 if the integer could not be parsed.
• int: Convert a string or numeric to an int
• int64: Convert a string or numeric to an int64
• float64: Convert a string or numeric to a float64

Defaults:

• default: Give a default value. Used like this: {{trim " "| default "empty"}}. Since trim produces an empty string, the default value is returned. For things with a length (strings, slices, maps), len(0) will trigger the default. For numbers, the value 0 will trigger the default. For booleans, false will trigger the default. For structs, the default is never returned (there is no clear empty condition). For everything else, nil value triggers a default.
• empty: Returns true if the given value is the zero value for that type. Structs are always non-empty.
• coalesce: Given a list of items, return the first non-empty one. This follows the same rules as 'empty'. {{ coalesce .someVal 0 "hello" }} will return .someVal if set, or else return "hello". The 0 is skipped because it is an empty value.
• compact: Return a copy of a list with all of the empty values removed. list 0 1 2 "" | compact will return [1 2]

OS:

• env: Read an environment variable.
• expandenv: Expand all environment variables in a string.

File Paths:

• base: Return the last element of a path. https://golang.org/pkg/path#Base
• dir: Remove the last element of a path. https://golang.org/pkg/path#Dir
• clean: Clean a path to the shortest equivalent name. (e.g. remove "foo/.." from "foo/../bar.html") https://golang.org/pkg/path#Clean
• ext: Get the extension for a file path: https://golang.org/pkg/path#Ext
• isAbs: Returns true if a path is absolute: https://golang.org/pkg/path#IsAbs

Encoding:

• b32enc: Encode a string into a Base32 string
• b32dec: Decode a string from a Base32 string
• b64enc: Encode a string into a Base64 string
• b64dec: Decode a string from a Base64 string

Data Structures:

• tuple: Takes an arbitrary list of items and returns a slice of items. Its tuple-ish properties are mainly gained through the template idiom, and not through an API provided here. WARNING: The implementation of tuple will change in the future.
• list: An arbitrary ordered list of items. (This is prefered over tuple.)
• dict: Takes a list of name/values and returns a map[string]interface{}. The first parameter is converted to a string and stored as a key, the second parameter is treated as the value. And so on, with odds as keys and evens as values. If the function call ends with an odd, the last key will be assigned the empty string. Non-string keys are converted to strings as follows: []byte are converted, fmt.Stringers will have String() called. errors will have Error() called. All others will be passed through fmt.Sprtinf("%v"). dicts are unordered.

List:

{{$t := list 1 "a" "foo"}}
{{index $t 2}}{{index $t 0 }}{{index $t 1}}
{{/* Prints foo1a *}}

Dict:

{{ $t := map "key1" "value1" "key2" "value2" }}
{{ $t.key2 }}
{{ /* Prints value2 *}}

Lists Functions:

These are used to manipulate lists: {{ list 1 2 3 | reverse | first }}

• first: Get the first item in a 'list'. 'list 1 2 3 | first' prints '1'
• last: Get the last item in a 'list': 'list 1 2 3 | last ' prints '3'
• rest: Get all but the first item in a list: 'list 1 2 3 | rest' returns '[2 3]'
• initial: Get all but the last item in a list: 'list 1 2 3 | initial' returns '[1 2]'
• append: Add an item to the end of a list: 'append $list 4' adds '4' to the end of '$list'
• prepend: Add an item to the beginning of a list: 'prepend $list 4' puts 4 at the beginning of the list.

Dict Functions:

These are used to manipulate dicts.

• set: Takes a dict, a key, and a value, and sets that key/value pair in the dict. set $dict $key $value. For convenience, it returns the dict, even though the dict was modified in place.
• unset: Takes a dict and a key, and deletes that key/value pair from the dict. unset $dict $key. This returns the dict for convenience.
• hasKey: Takes a dict and a key, and returns boolean true if the key is in the dict.
• pluck: Given a key and one or more maps, get all of the values for that key.
• keys: Get an array of all of the keys in a dict. Order is not guaranteed.
• pick: Select just the given keys out of the dict, and return a new dict.
• omit: Return a dict without the given keys.

Reflection:

• typeOf: Takes an interface and returns a string representation of the type. For pointers, this will return a type prefixed with an asterisk(*). So a pointer to type Foo will be *Foo.

• typeIs: Compares an interface with a string name, and returns true if they match. Note that a pointer will not match a reference. For example *Foo will not match Foo.

• typeIsLike: returns true if the interface is of the given type, or is a pointer to the given type.

• kindOf: Takes an interface and returns a string representation of its kind.

• kindIs: Returns true if the given string matches the kind of the given interface.

  Note: None of these can test whether or not something implements a given interface, since doing so would require compiling the interface in ahead of time.

Math Functions:

Integer functions will convert integers of any width to int64. If a string is passed in, functions will attempt to conver with strconv.ParseInt(s, 1064). If this fails, the value will be treated as 0.

• add1: Increment an integer by 1
• add: Sum integers. add 1 2 3 renders 6
• sub: Subtract the second integer from the first
• div: Divide the first integer by the second
• mod: Module of first integer divided by second
• mul: Multiply integers integers
• max (biggest): Return the biggest of a series of integers. max 1 2 3 returns 3.
• min: Return the smallest of a series of integers. min 1 2 3 returns 1.

Cryptographic Functions:

• derivePassword: Derive a password from the given parameters according to the "Master Password" algorithm (http://masterpasswordapp.com/algorithm.html) Given parameters (in order) are: counter (starting with 1), password_type (maximum, long, medium, short, basic, or pin), password, user, and site. The following line generates a long password for the user "user" and with a master-password "password" on the site "example.com": {{ derivePassword 1 "long" "password" "user" "example.com" }}

Principles:

The following principles were used in deciding on which functions to add, and determining how to implement them.

• Template functions should be used to build layout. Therefore, the following types of operations are within the domain of template functions:
  • Formatting
  • Layout
  • Simple type conversions
  • Utilities that assist in handling common formatting and layout needs (e.g. arithmetic)
• Template functions should not return errors unless there is no way to print a sensible value. For example, converting a string to an integer should not produce an error if conversion fails. Instead, it should display a default value that can be displayed.
• Simple math is necessary for grid layouts, pagers, and so on. Complex math (anything other than arithmetic) should be done outside of templates.
• Template functions only deal with the data passed into them. They never retrieve data from a source.
• Finally, do not override core Go template functions.