README ¶
Boilerplate
Boilerplate is a tool for generating files and folders ("boilerplate") from a set of templates.
Example use cases:
- Scaffold out a new repo, folder, or file.
- Fill in boilerplate sections in your code files, such as including a legal disclaimer or license at the top of each source file, or updating a version number in a file after each build.
- Embed code snippets from actual source files in documentation. Most READMEs have code copy/pasted into them and that code often has syntax errors or goes out of date. Now you can keep those code examples in normal source files which are built & tested, and embed parts of those files dynamically in your docs.
See Introducing Boilerplate for a quick introduction.
Example: creating a new template
Create a folder called website-boilerplate
and put a file called boilerplate.yml
in it:
variables:
- name: Title
- name: WelcomeText
description: Enter the welcome text for the website
- name: ShowLogo
description: Should the website show the logo?
type: bool
default: true
This file defines 3 variables: Title
, WelcomeText
, and ShowLogo
. When you run Boilerplate, it will prompt
the user for each one.
Next, create an index.html
in the website-boilerplate
folder that uses these variables using Go
Template syntax:
<html>
<head>
<title>{{.Title}}</title>
</head>
<body>
<h1>{{.WelcomeText}}</h1>
{{if .ShowLogo}}<img src="logo.png">{{end}}
</body>
</html>
Copy an image into the website-boilerplate
folder and call it logo.png
.
Finally, run boilerplate
, setting the --template-url
to website-boilerplate
and --output-folder
to the path
where you want the generated code to go:
boilerplate --template-url /home/ubuntu/website-boilerplate --output-folder /home/ubuntu/website-output
Title
Enter a value [type: string]: Boilerplate Example
WelcomeText
Enter the welcome text for the website
Enter a value [type: string]: Welcome!
ShowLogo
Should the website show the logo?
Enter a [type: bool]: true
Generating /home/ubuntu/website-output/index.html
Copying /home/ubuntu/website-output/logo.png
Boilerplate copies any files from the --template-url
into the --output-folder
, passing them through the
Go Template engine along the way. After running the command above, the
website-output
folder will contain a logo.png
(unchanged from the original) and an index.html
with the
following contents:
<html>
<head>
<title>Boilerplate</title>
</head>
<body>
<h1>Welcome!</h1>
<img src="logo.png">
</body>
</html>
You can also run Boilerplate non-interactively, which is great for automation:
boilerplate \
--template-url /home/ubuntu/website-boilerplate \
--output-folder /home/ubuntu/website-output \
--non-interactive \
--var Title="Boilerplate Example" \
--var WelcomeText="Welcome!" \
--var ShowLogo="true"
Generating /home/ubuntu/website-output/index.html
Copying /home/ubuntu/website-output/logo.png
Of course, Boilerplate can be used to generate any type of project, and not just HTML, so check out the examples folder for more examples and the Working with Boilerplate section for full documentation.
Install
Download the latest binary for your OS here.
You can find older versions on the Releases Page.
Features
- Interactive mode: Boilerplate interactively prompts the user for a set of variables defined in a
boilerplate.yml
file and makes those variables available to your project templates during copying. - Non-interactive mode: Variables can also be set non-interactively, via command-line options, so that Boilerplate can be used in automated settings (e.g. during automated tests).
- Flexible templating: Boilerplate uses Go Template for templating, which gives you the ability to do formatting, conditionals, loops, and call out to Go functions. It also includes helpers for common tasks such as loading the contents of another file.
- Variable types: Boilerplate variables support types, so you have first-class support for strings, ints, bools,
- Validations: Boilerplate provides a set of validations for a given variable that user input must satisfy.
- Variable presentation order: Boilerplate allows you to define the relative presentation order of a set of variables. lists, maps, and enums.
- Scripting: Need more power than static templates and variables? Boilerplate includes several hooks that allow you to run arbitrary scripts.
- Cross-platform: Boilerplate is easy to install (it's a standalone binary) and works on all major platforms (Mac, Linux, Windows).
Working with boilerplate
When you run Boilerplate, it performs the following steps:
- Read the
boilerplate.yml
file in the folder specified by the--template-url
option to find all defined varaibles. - Gather values for the variables from any
--var
and--var-file
options that were passed in and prompting the user for the rest (unless the--non-interactive
flag is specified). - Copy each file from
--template-url
to--output-folder
, running each non-binary file through the Go Template engine with the map of variables as the data structure.
Learn more about boilerplate in the following sections:
- Boilerplate command line options
- The boilerplate.yml file
- Variables
- Dependencies
- Hooks
- Skip Files
- Templates
- Validations
- Variable Ordering
- Alternative Template Engines (EXPERIMENTAL)
- Template helpers
- Deprecated helpers
- Partials
Boilerplate command line options
The boilerplate
binary supports the following options:
--template-url URL
(required): Generate the project from the templates inURL
. This can be a local path, or a go-getter compatible URL for remote templates (e.g.,git@github.com:gruntwork-io/boilerplate.git//examples/for-learning-and-testing/include?ref=main
).--output-folder
(required): Create the output files and folders inFOLDER
.--non-interactive
(optional): Do not prompt for input variables. All variables must be set via--var
and--var-file
options instead.--var NAME=VALUE
(optional): UseNAME=VALUE
to set variableNAME
toVALUE
. May be specified more than once.--var-file FILE
(optional): Load variable values from the YAML fileFILE
. May be specified more than once.--missing-key-action ACTION
(optional): What to do if a template looks up a variable that is not defined. Must be one of:invalid
(render the text ""),zero
(render the zero value for the variable), orerror
(return an error and exit immediately). Default:error
.--missing-config-action ACTION
(optional): What to do if a template folder does not have aboilerplate.yml
file. Must be one of:exit
(return an error and exit immediately) orignore
(log a warning and process the template folder without any variables). Default:exit
.--disable-hooks
: If this flag is set, no hooks will execute.--disable-shell
: If this flag is set, noshell
helpers will execute. They will instead return the text "replace-me".--disable-dependency-prompt
(optional): Do not prompt for confirmation to include dependencies. Has the same effect as --non-interactive, without disabling variable prompts. Default:false
.--help
: Show the help text and exit.--version
: Show the version and exit.
Some examples:
Generate a project in ~/output from the templates in ~/templates:
boilerplate --template-url ~/templates --output-folder ~/output
Generate a project in ~/output from the templates in ~/templates, using variables passed in via the command line:
boilerplate --template-url ~/templates --output-folder ~/output --var "Title=Boilerplate" --var "ShowLogo=false"
Generate a project in ~/output from the templates in ~/templates, using variables read from a file:
boilerplate --template-url ~/templates --output-folder ~/output --var-file vars.yml
Generate a project in ~/output from the templates in this repo's include
example dir, using variables read from a file:
boilerplate --template-url "git@github.com:gruntwork-io/boilerplate.git//examples/for-learning-and-testing/include?ref=main" --output-folder ~/output --var-file vars.yml
The boilerplate.yml file
The boilerplate.yml
file is used to configure boilerplate
. The file is optional. If you don't specify it, you can
still use Go templating in your templates so long as you specify the --missing-config-action ignore
option, but no
variables or dependencies will be available.
boilerplate.yml
uses the following syntax:
required_version: <VERSION_CONSTRAINT>
variables:
- name: <NAME>
description: <DESCRIPTION>
type: <TYPE>
options:
- <CHOICE>
- <CHOICE>
default: <DEFAULT>
reference: <NAME>
dependencies:
- name: <DEPENDENCY_NAME>
template-url: <FOLDER>
output-folder: <FOLDER>
skip: <CONDITION>
dont-inherit-variables: <BOOLEAN>
for_each: <LIST>
for_each_reference: <NAME>
variables:
- name: <NAME>
description: <DESCRIPTION>
type: <TYPE>
default: <DEFAULT>
hooks:
before:
- command: <CMD>
args:
- <ARG>
env:
<KEY>: <VALUE>
skip: <CONDITION>
after:
- command: <CMD>
args:
- <ARG>
env:
<KEY>: <VALUE>
skip: <CONDITION>
partials:
- <GLOB>
- <GLOB>
Here's an example:
variables:
- name: Description
description: Enter the description of this template
- name: Version
description: Enter the version number that will be used by the docs dependency
- name: Title
description: Enter the title for the dependencies example
- name: WelcomeText
description: Enter the welcome text used by the website dependency
- name: ShowLogo
description: Should the webiste show the logo (true or false)?
type: bool
default: true
dependencies:
- name: docs
template-url: ../docs
output-folder: ./docs
variables:
- name: Title
description: Enter the title of the docs page
- name: website
template-url: ../website
output-folder: ./website
variables:
- name: Title
description: Enter the title of the website
skip_files:
- path: .ignore-me
- path: subfolder/README.md
if: {{ not .ShowLogo }}
engines:
- path: subfolder/foo.json.jsonnet
template_engine: jsonnet
partials:
- ../html/*.html
- ../css/*.css
- ../other/somefile.html
Required Version: A version constraint string in the same format as Terraform that can be used to specify what versions of Boilerplate are supported by the config.
Variables: A list of objects (i.e. dictionaries) that define variables. Each variable may contain the following keys:
name
(Required): The name of the variable.description
(Optional): The description of the variable.boilerplate
will show this description to the user when prompting them for a value.type
(Optional): The type of the variable. Must be one of:string
,int
,float
,bool
,map
,list
,enum
. If unspecified, the default isstring
.options
(Optional): If thetype
isenum
, you can specify a list of valid options. Each option must be a string.default
(Optional): A default value for this variable. The user can just hit ENTER at the command line to use the default value, if one is provided. If running Boilerplate with the--non-interactive
flag, the default is used for this value if no value is provided via the--var
or--var-file
options.reference
(Optional): The name of another variable whose value should be used for this one.
See the Variables section for more info.
Dependencies: A list of objects (i.e. dictionaries) that define other boilerplate
templates to execute before
executing the current one. Each dependency may contain the following keys:
name
(Required): A unique name for the dependency.template-url
(Required): Runboilerplate
on the templates in this folder. This path is relative to the current template.output-folder
(Required): Create the output files and folders in this folder. This path is relative to the output folder of the current template.skip
(Optional): Skip this dependency if this condition, which can use Go templating syntax and boilerplate variables, evaluates to the stringtrue
. This is useful to conditionally enable or disable dependencies.dont-inherit-variables
(Optional): By default, any variables already set as part of the currentboilerplate.yml
template will be reused in the dependency, so that the user is not prompted multiple times for the same variable. If you set this option tofalse
, then the variables from the parent template will not be reused.variables
: If a dependency contains a variable of the same name as a variable in the rootboilerplate.yml
file, but you want the dependency to get a different value for the variable, you can specify overrides here. Note that these variables will not influence the boilerplate prompts.var_files
: If you want to set the variables for the dependency based on a var file, you can provide a list of var file paths to include. The path is assumed to be relative to the current boilerplate.yml, but it is recommended to use thetemplateFolder
helper function to be explicit. Note that the order of preference for variables are (top most have highest precedence - aka override all):- Top level variables set on the CLI.
- Var files set on the dependency.
- Defaults set on dependency variables (the
variables
field of the dependency). - Defaults set on root variables.
- Defaults set within the dependency boilerplate config.
for_each
: If you set this to a list of values,boilerplate
will loop over each value, and render this dependency once for each value. This allows you to dynamically render a dependency multiple times based on user input. The current value in the loop will be available as the variable__each__
, available to both your Go templating and in otherdependencies
params: e.g., you could reference{{ .__each__ }}
inoutput-folder
to render to each iteration to a different folder.for_each_reference
: The name of another variable whose value should be used as thefor_each
value.
See the Dependencies section for more info.
Partials: Use partials to include reusable templates. Partials are defined using a list of glob patterns.
- Globs are matched using the Go
filepath.Glob
function - In the event of a template name collision (e.g. multiple templates are defined with the same name), the last one wins.
See the Partials section for more info.
Skip Files: Use skip_files to specify files in the template folder that should not be rendered. The path
field
is the relative path from the template folder root (where the boilerplate.yml
file is defined) of the file that should
be excluded. You can conditionally skip the file using the if
field, which should either be a YAML boolean value
(true
or false
), or Go templating syntax (which can use the boilerplate variables) that evaluates to the string
values "true"
or "false"
.
See the Skip Files section for more info.
Engines: Use engines to specify files in the template folder that should be rendered with an alternative
templating engine. The path
field is the relative path from the template folder root (where the boilerplate.yml
file
is defined) of the file that should use the alternative template engine.
See the Alternative Template Engines (EXPERIMENTAL) section for more info.
Hooks: Boilerplate provides hooks to execute arbitrary shell commands. There are two types of hooks:
before
(Optional): A list of scripts to execute before any template rendering has started.after
(Optional): A list of scripts to execute after all template rendering has completed.
See the Hooks section for more info.
Variables
You must provide a value for every variable defined in boilerplate.yml
, or project generation will fail. There are
five ways to provide a value for a variable:
-
--var
option(s) you pass in when calling boilerplate. Example:boilerplate --var Title=Boilerplate --var ShowLogo=false
. To specify a complex type like a map or a list on the command-line, use YAML syntax (preferably the shorthand variety to keep it a one-liner). For example--var foo='{key: "value"}' --var bar='["a", "b", "c"]'
. If you want to specify the value of a variable for a specific dependency, use the<DEPENDENCY_NAME>.<VARIABLE_NAME>
syntax. For example:boilerplate --var Description='Welcome to my home page!' --var about.Description='About Us' --var ShowLogo=false
. -
--var-file
option(s) you pass in when calling boilerplate. Example:boilerplate --var-file vars.yml
. The vars file must be a simple YAML file that defines key, value pairs, where the key is the name of a variable (or<DEPENDENCY_NAME>.<VARIABLE_NAME>
for a variable in a dependency) and the value is the value to set for that variable. Example:Title: Boilerplate ShowLogo: false Description: Welcome to my home page! about.Description: Welcome to my home page! ExampleOfAMap: key1: value1 key2: value2 ExampleOfAList: - value1 - value2
-
Manual input. If no value is specified via the
--var
or--var-file
flags, Boilerplate will interactively prompt the user to provide a value. Note that the--non-interactive
flag disables this functionality. -
Defaults defined in
boilerplate.yml
. The final fallback is the optionaldefault
that you can include as part of the variable definition inboilerplate.yml
. -
An environment variable with the name
BOILERPLATE_<VARIABLE_NAME>
. For example, if you have a variable calledTitle
, you can set the value of this variable by setting the environment variableBOILERPLATE_Title
(note the case sensitivity). This is useful for automation and CI/CD pipelines.
Note that variables can reference other variables using Go templating syntax:
variables:
- name: Foo
default: foo
- name: Bar
default: "{{ .Foo }}-bar"
If you rendered {{ .Bar }}
with the variables above, you would get foo-bar
. Note that this will always
return a string. If you want to reference another variable of a non-string type (e.g. a list), use the reference
keyword:
variables:
- name: Foo
type: list
default:
- 1
- 2
- 3
- name: Bar
type: list
reference: Foo
In the example above, the Bar
variable will be set to the same (list) value as Foo
.
Dependencies
Specifying dependencies within your boilerplate.yml
files allows you to chain multiple boilerplate
templates
together. This allows you to create more complicated projects from simpler pieces.
Note the following:
-
Recursive dependencies: Dependencies can include other dependencies. For example, the
boilerplate.yml
in folder A can include folder B in itsdependencies
list, theboilerplate.yml
in folder B can include folder C in itsdependencies
list, and so on. -
Inheriting variables: You can define all your common variables in the root
boilerplate.yml
and any variables with the same name in theboilerplate.yml
files of yourdependencies
list will reuse those variables instead of prompting the user for the same value again. -
Variable conflicts: Sometimes, two dependencies use a variable of the same name, but you want them to have different values. To handle this use case, you can define custom
variable
blocks for each dependency andboilerplate
will prompt you for each of those variables separately from the root ones. You can also use the<DEPENDENCY_NAME>.<VARIABLE_NAME>
syntax as the name of the variable with the-var
flag and inside of a var file to provide a value for a variable in a dependency. -
Interpolation: You may use interpolation in the
template-url
andoutput-folder
parameters of your dependencies. This allows you to use specify the paths to your template and output folders dynamically. -
Conditional dependencies: You can enable or disable a dependency using the
skip
parameter, which supports Go templating syntax and boilerplate variables. If theskip
parameter evaluates to the stringtrue
, the dependency will be skipped; otherwise, it will be rendered. Example:variables: - name: Foo type: bool - name: Bar type: bool dependencies: - name: conditional-dependency-example template-url: ../foo output-folder: foo # Skip this dependency if both .Foo and .Bar are set to true skip: "{{ and .Foo .Bar }}"
-
Looping over dependencies: You can render a dependency multiple times, dynamically, based on user input, via the
for_each
orfor_each_reference
parameter. Example:variables: - name: environments description: The environments to deploy into (e.g., dev, stage, prod) type: list default: - dev - stage - prod dependencies: - name: loop-dependency-example template-url: ../terraform # Render this dependency once for each environment the user specifies for_each_reference: environments # Render the dependency to an output folder that includes the environment name output-folder: "live/{{ .__each__ }}" variables: - name: ServerName description: The name to use for the EC2 instance (for its Name tag) type: string # Use the environment name in the server name default: "example-{{ .__each__ }}"
-
Confirming dependency includes: By default in interactive mode, the user must confirm to include each dependency. If
--non-interactive
is set, dependencies will be included automatically, so long asskip
is false. If you'd like to keep interactive mode enabled, but disable dependency confirmation, set--disable-dependency-prompt
.
Hooks
You can specify hooks
in boilerplate.yml
to tell Boilerplate to execute arbitrary shell commands.
Note the following:
-
The
before
hook allows you to run scripts before Boilerplate has started rendering. -
The
after
hook allows you to run scripts after Boilerplate has finished rendering. -
Each hook consists of a
command
to execute (required), a list ofargs
to pass to that command (optional), a map of environment variables inenv
to set for the command (optional), and the working directorydir
in which to run the command (optional). Example:before: - command: echo args: - Hello - World env: FOO: BAR dir: "/foo/bar"
-
You can use Go templating syntax in
command
,args
,env
, anddir
. For example, you can pass Boilerplate variables to your scripts as follows:before: - command: foo.sh args: - {{ .SomeVariable }} - {{ .AnotherVariable }}
-
By default, Boilerplate runs your
command
with the working directory set to the--template-url
option. You can override this with thedir
parameter. For example, here is how you can set it to a sub-folder of the output folder:after: - command: some-command dir: "{{ outputFolder }}/foo/bar"
-
skip
(Optional): Skip this hook if this condition, which can use Go templating syntax and boilerplate variables, evaluates to the stringtrue
. This is useful to conditionally enable or disable dependencies. -
For an alternative way to execute commands, see the
shell
helper in template helpers.
Skip Files
You can specify files that should be excluded from the rendered output using the skip_files
section in
boilerplate.yml
. This is most useful when you have templates that need to conditionally exclude files from the
rendered folder list.
The skip_files
section is a list of objects with the fields path
, not_path
, and if
, where one of path
or
not_path
is required. When path
is set, all files that match the path
attribute will be skipped, while when
not_path
is set, all files that DO NOT match the not_path
attribute are skipped (in other words, only paths that
match not_path
are kept).
if
can be used to conditionally skip a file from the template folder, and it defaults to true
. That is, when if
is
omitted, the file at the path is always excluded from the output. Note that path
and not_path
are always the
relative path from the template root.
All three attributes (path
, not_path
, and if
) support Go templating syntax with access to boilerplate
variables and template helpers.
Consider the following boilerplate template folder:
.
├── boilerplate.yml
├── BOILERPLATE_README.md
└── docs
├── README_WITH_ENCRYPTION.md
└── README_WITHOUT_ENCRYPTION.md
Suppose that you wanted to conditionally select which README to render based on some variable. You can use skip_files
to implement this logic:
variables:
- name: UseEncryption
type: bool
skip_files:
- path: "BOILERPLATE_README.md"
- path: "docs/README_WITH_ENCRYPTION.md"
if: "{{ not .UseEncryption }}"
- path: "docs/README_WITHOUT_ENCRYPTION.md"
if: "{{ .UseEncryption }}"
- not_path: "docs/**/*"
if: "{{ .DocsOnly }}"
This will:
- Always skip rendering
BOILERPLATE_README.md
. - Skip rendering
docs/README_WITHOUT_ENCRYPTION.md
ifUseEncryption
is set totrue
. - Skip rendering
docs/README_WITH_ENCRYPTION.md
ifUseEncryption
is set tofalse
. - If
DocsOnly
is set totrue
, only render thedocs
folder.
For a more concise specification, you can use glob syntax in the path
to match multiple paths in one entry:
skip_files:
- path: "docs/**/*"
Templates
Boilerplate puts all the variables into a Go map where the key is the name of the variable and the value is what
the user provided. It then starts copying files from the --template-url
into the --output-folder
, passing each
non-binary file through the Go Template engine, with the variable map as a data structure.
For example, if you had a variable called Title
in your boilerplate.yml
file, then you could access that variable
in any of your templates using the syntax {{.Title}}
. You can also use Go template syntax to do
if-statements, for loops, and use the provided template helpers.
You can even use Go template syntax and boilerplate variables in the names of your files and folders. For example, if
you were using boilerplate
to generate a Java project, your template folder could contain the path
com/{{.PackageName}}/MyFactory.java
. If you run boilerplate
against this template folder and enter
"gruntwork" as the PackageName
, you'd end up with the file com/gruntwork/MyFactory.java
.
Validations
Boilerplate allows you to specify a set of validations when defining a variable. When a user is prompted for a variable that has validations defined, their input must pass all defined validations. If the user's input does not pass all validations, they'll be presented with real-time feedback on exactly which rules their submission is failing. Once a user's submission passes all defined validations, Boilerplate will accept their submitted value.
Here's an example prompt for a variable with validations that shows how invalid submissions are handled:
Here's an example demonstating how to specify validations when defining your variables:
variables:
- name: CompanyName
description: Enter the name of your organization.
default: ""
type: string
validations:
- required
- length-5-22
- alphanumeric
This boilerplate.yml
snippet defines a variable, CompanyName
which:
- Must be supplied by the user. No empty or nil values will be accepted.
- Must have a length between 5 and 22 characters
- Must contain only alphanumeric characters (no special characters)
Currently supported validations
Boilerplate uses the go-ozzo/ozzo-validation
library. The following validations are currently supported:
- "required" - field cannot be empty
- "length-{min-int}-{max-int}" - field must be between ${min-int} and ${max-int} characters in length
- "url" - field must be a valid URL
- "email" - field must be a valid email address
- "alpha" - field must contain English letters only
- "digit" - field must contain digits only
- "countrycode2" - field must be an ISO3166 Alpha 2 Country code
- "semver" - field must be a valid semantic version
Variable Ordering
Boilerplate allows you to define the relative order in which a set of variables should be presented to the user when prompting for human input.
Here's an example demonstrating how to define the relative order of a set of variables:
variables:
- name: WebsiteURL
order: 0
description: Enter the URL to your homepage
- name: ImagePath:
order: 1
description: Enter the full filepath to your logo image
- name: ProfileName
order: 2
description: Enter the display name for your user
Alternative Template Engines (EXPERIMENTAL)
Boilerplate has experimental support for the following alternative template engines:
To specify an alternative template engine, you can use the engines
directive to provide a path glob that matches the
files that should be fed through the alternative engine. For example, the following boilerplate configuration makes it
so that any file with the .jsonnet
extension will be fed through the jsonnet template engine:
engines:
- path: "**/*.jsonnet"
template_engine: jsonnet
Note that alternative template engines are currently only supported for processing individual files, and can not be used for parsing boilerplate directives in the config file or directory names.
See below for more information on each of the template engines supported:
IMPORTANT: Support for template helpers are limited to the go templating engine at this time. Some limited functions may be available depending on the template engine. See the information for the templating engine to know which functions are supported.
Jsonnet is a data template engine optimized for generating json data. Unlike go templating, jsonnet has many features that make it more friendly to write such as:
- Imports
- Functions
- Better error handling
- Editor support
When boilerplate processes jsonnet templates, the variables are passed through as a Top Level
Argument under the name boilerplateVars
. This
means that every jsonnet template must be defined in a way to handle the TLA argument. For example:
function(boilerplateVars) {
person: {
name: boilerplateVars.Name,
},
}
Boilerplate will also make available the following helpers as external variables:
templateFolder
: Set to the value of the template working dir. This is the same as what thetemplateFolder
boilerplate helper function returns.outputFolder
: Set to the value of the output folder where the templates are rendered. This is the same as what theoutputFolder
boilerplate helper function returns.
While the jsonnet
template engine does not support the boilerplate helper functions, it does have access to the
Jsonnet standard library. You can also import any libsonnet
library in your
jsonnet template, including those installed with jsonnet-bundlery.
Note that to ensure you can have editor assistance while modifying jsonnet files, the jsonnet template engine in
boilerplate will strip the extension suffix .jsonnet
from the output file path. E.g., if your template folder
contained:
.
├── boilerplate.yml
└── data.json.jsonnet
The output folder will be:
.
└── data.json
Template helpers
Your templates have access to all the standard functionality in Go Template, including conditionals, loops, and functions.
Additionally, boilerplate ships with sprig (version 3.2.1
), the standard
library of template functions. You can view all the functions available in sprig
here. Note that there are some differences for some functions due to backwards
compatibility. Take a look at Deprecated helpers.
Boilerplate also includes several custom helpers that you can access that enhance the functionality of sprig:
-
snippet <PATH> [NAME]
: Returns the contents of the file atPATH
as a string. If you specify the second argument,NAME
, only the contents of the snippet with that name will be returned. A snippet is any text in the file surrounded by a line on each side of the format "boilerplate-snippet: NAME" (typically using the comment syntax for the language). For example, here is how you could define a snippet named "foo" in a Java file:String str = "this is not part of the snippet"; // boilerplate-snippet: foo String str2 = "this is part of the snippet"; return str2; // boilerplate-snippet: foo
-
include <PATH> <VARIABLES>
: Returns the contents of the file atPATH
after rendering it through the templating engine with the provided variables, as a string (unlikesnippet
, which returns the contents of the file verbatim). Use.
to pass the current variables to the included template. E.g:{{ include "../source-template.snippet" . }}
-
replaceOne OLD NEW
: Replace the first occurrence ofOLD
withNEW
. This is a literal replace, not regex. -
replaceAll OLD NEW
: Replace all occurrences ofOLD
withNEW
. This is a literal replace, not regex. -
roundInt FLOAT
: RoundFLOAT
to the nearest integer. E.g. 1.5 becomes 2. -
ceilInt FLOAT
: Round upFLOAT
to the nearest integer. E.g. 1.5 becomes 2. -
floorInt FLOAT
: Round downFLOAT
to the nearest integer. E.g. 1.5 becomes 1. -
dasherize STRING
: ConvertSTRING
to a lower case string separated by dashes. E.g. "foo Bar baz" becomes "foo-bar-baz". -
camelCaseLower STRING
: ConvertSTRING
to a camel case string where the first letter is lower case. E.g. "foo Bar baz" becomes "fooBarBaz". -
plus NUM NUM
: Add the two numbers. Unlike add in sprig, this supports float. -
minus NUM NUM
: Subtract the two numbers. Unlike sub in sprig, this supports float. -
times NUM NUM
: Multiply the two numbers. Unlike mul in sprig, this supports float. -
divide NUM NUM
: Divide the two numbers. Unlike div in sprig, this supports float. -
numRange START END INCREMENT
: Generate a slice from START to END, incrementing by INCREMENT. This provides a simple way to do a for-loop over a range of numbers. -
keysSorted MAP
: Return a slice that contains all the keys in the given MAP in alphanumeric sorted order. Use the built-in Go template helper.index
to look up these keys in the map. -
shell CMD ARGS...
: Execute the given shell command, passing it the given args, and render whatever that command prints to stdout. The working directory for the command will be set to the directory of the template being rendered, so you can use paths relative to the file from which you are calling theshell
helper. Any argument you pass of the formENV:KEY=VALUE
will be set as an environment variable for the command rather than an argument. For another way to execute commands, see hooks. -
templateFolder
: Return the value of the template working dir. This is the value of the--template-url
command-line option if local template, or the download dir if remote template. Useful for building relative paths. -
outputFolder
: Return the value of the--output-folder
command-line option. Useful for building relative paths. -
envWithDefault NAME DEFAULT
: Render the value of environment variableNAME
. If that environment variable is empty or not defined, renderDEFAULT
instead. -
pathExists PATH
: Returns true if the given path exists on the file system. -
templateIsDefined NAME
: Returns a boolean indicating if template calledNAME
is known. Use this to conditionally include one boilerplate template with another. Most often useful along with partials. -
toYaml
: Encodes an input variable as a YAML string. Similar to thetoJson
function in sprig.
Deprecated helpers
These helpers are deprecated. They are currently available for backwards compatibility, but may be removed in future versions. Please use the alternative supported forms listed in the description.
downcase STRING
: Same functionality as lower in sprig.upcase STRING
: Same functionality as upper in sprig.capitalize STRING
: Same functionality as title in sprig.snakeCase STRING
: Same functionality as snakecase in sprig.camelCase STRING
: Same functionality as camelcase in sprig.
The following functions overlap with sprig, but have different functionality. There is an equivalent function listed above under a different name. These point to the boilerplate implementations for backwards compatibility. Please migrate to using the new naming scheme, as they will be updated to use the sprig versions in future versions of boilerplate.
round
: In boilerplate,round
returns the integer form as opposed to float. E.g{{ round 123.5555 }}
will return124
. The following supported alternative functions are available:roundFloat
: The sprig version of round, which supports arbitrary decimal rounding. E.g{{ round 123.5555 3 }}
returns123.556
. Note that{{ round 123.5555 0 }}
returns124.0
.roundInt
: Another name for the boilerplate version ofround
. Use this if you would like to keep old behavior.
ceil
andfloor
: In boilerplate,ceil
andfloor
return integer forms as opposed to floats. E.g{{ ceil 1.1 }}
returns2
, as opposed to2.0
in the sprig version. The following supported alternative functions are available:env
: In boilerplate,env
supports returning a default value if the environment variable is not defined. The following supported alternative functions are available:readEnv
: The sprig version of env. This always returns empty string if the environment variable is undefined.envWithDefault
: Another name for the boilerplate version ofenv
. Use this if you would like to keep old behavior.
keys
: In boilerplate,keys
returns the keys of the map in sorted order. The following supported alternative functions are available:keysUnordered
: The sprig version of keys. This returns the list of keys in no particular order, and there is no guarantee that the order of the returned list is consistent.keysSorted
: Another name for the boilerplate version ofkeys
. Use this if you would like to keep old behavior.
replace
: In boilerplate,replace
only replaces the first occurrence in the string, as opposed to all occurrences as in sprig. The following supported alternative functions are available:replaceAll
: The sprig version of replace.replaceOne
: Another name for the boilerplate version ofreplace
. Use this if you would like to keep old behavior.
slice
: In boilerplate,slice
returns a list of numbers in the provided range. E.g{{ slice 1 5 1 }}
returns the list[1, 2, 3, 4]
. The following supported alternative functions are available:sliceList
: The sprig version of slice, which returns the slice of the given list. E.g{{ slice list n m }}
returnslist[n:m]
.numRange
: Another name for the boilerplate version ofslice
. Use this if you would like to keep old behavior.
trimPrefix
andtrimSuffix
: In boilerplate,trimPrefix
andtrimSuffix
takes the base string first. E.g{{ trimPrefix hello-world hello }}
returns-world
. The following supported alternative functions are available:trimPrefixSprig
andtrimSuffixSprig
: The sprig version of trimPrefix and trimSuffix. Unlike the boilerplate version, this takes the trim text first so that you can pipeline the trimming. E.g{{ "hello-world" | trimPrefix "hello" }}
returns{{ -world }}
.trimPrefixBoilerplate
andtrimSuffixBoilerplate
: Another name for the boilerplate versions oftrimPrefix
andtrimSuffix
. Use this if you would like to keep old behavior.
Partials
Partials help to keep templates DRY. Using partials, you can define templates in external files, and then use those templates over and over again in other templates. Partials are common among templating engines, such as in Hugo.
Let's start with a simple example. In an HTML document, we might want to have a common set of meta
tags to reuse throughout our site:
<html>
<head>
<meta charset="UTF-8">
<meta name="author" content="Gruntwork">
</head>
<body>
<h1>Welcome to this page!</h1>
<img src="logo.png">
</body>
</html>
Rather than add these tags in a <head>
section within each and every file, we could define a partial, then reuse it throughout the site.
We define the header in partials/header.html
:
{{ define "header" }}
<head>
<meta charset="UTF-8">
<meta name="author" content="Gruntwork">
</head>
{{ end }}
Then we set up the structure in templates/boilerplate.yml
:
partials:
- ../partials/*.html
In templates/page.html
:
<html>
{{ template "header" }}
<body>
<h1>Welcome to this page!</h1>
<img src="logo.png">
</body>
</html>
The contents of the header
template will be rendered within page.html
and any other page in which we call the header partial.
Let's see a slightly more involved example.
<html>
<head>
<title>Welcome!</title>
</head>
<body>
<h1>Welcome to this page!</h1>
<img src="logo.png">
</body>
</html>
The example above shows the HTML for a web page, with a title, a welcome message, and a logo. Now, if we wanted to have another page showing a different title and body, we'd have to duplicate all of that content.
In the example below, we'll create a partial that represents the basic layout of the site, then reuse that layout for each page. First, we create a directory structure to keep everything organized:
.
├── partials
│ └── layout.html
└── template
├── about
│ ├── about.html
│ └── boilerplate.yml
└── root
├── boilerplate.yml
└── index.html
In partials/layout.html
, we create the basic page layout:
{{ define "basic_layout" }}
<html>
<head>
<title>{{ .Title }}</title>
</head>
<body>
{{ template "body" . }}
</body>
</html>
{{ end }}
Now, in each of the pages on the site, we can reuse this layout. For example, from the site's root, we want the welcome
page. We create the boilerplate.yml
first:
partials:
- ../../partials/*.html
variables:
- name: Title
description: A title for the page.
default: "Welcome!"
Now we can use the layout within our index.html
:
{{- define "body" -}}
<h1>This is index.html.</h1>
<img src="logo.png">
{{- end -}}
{{- template "basic_layout" . -}}
When we run boilerplate
, basic_layout
template will be rendered with the contents of the index.html
. Then we can
use the same layout for the about page, with its corresponding boilerplate.yml
.
Contents of about/boilerplate.yml
:
partials:
- ../../partials/*.html
variables:
- name: Title
description: A title for the page.
default: "About"
about/about.html
:
{{- define "body" -}}
<h1>This is about.html.</h1>
{{- end -}}
{{- template "basic_layout" . -}}
Partials do not need to be located in a magic partials
directory. Partials can be located anywhere and referred to using relative
paths.
The list of partials is a glob that can match multiple files. The content of all of the files that match the globs will be parsed when rendering the final template. For example, you could match many HTML files at once with:
partials:
- ../../html/*.html
- ../../css/*.css
You can use the template definitions from any of the included partials throughout your templates.
You can use Go templating syntax in partial paths. For example, you can define a convenenience variable for a relative path to make the paths slightly easier to read:
variables:
- name: TemplatesRoot
description: A convenience variable identify the relative path to the root of the templates directory.
default: ../../../../
partials:
- "{{ .TemplatesRoot }}/html/*.html"
- "{{ .TemplatesRoot }}/css/*.css"
Alternative project generators
Before creating Boilerplate, we tried a number of other project generators, but none of them met all of our requirements. We list these alternatives below as a thank you to the creators of those projects for inspiring many of the ideas in Boilerplate and so you can try out other projects if Boilerplate doesn't work for you:
- cookiecutter: Project generator written in Python. Uses Jinja templates,
which are reasonably pleasant to work with, and has a huge community. However, the dependency on Python makes
cross-platform usage tricky, and the
cookiecutter.json
file is quite limited in what you can do. - yeoman: Project generator written in JavaScript. Good UI and huge community. However, very focused on generating web projects, and creating new generators is complicated and built around NPM. Not clear if it supports non-interactive mode.
- plop: Project generator written in JavaScript. Good UI and templating features. Does not support non-interactive mode.
- giter8: Project generator written in Scala. A good option if you're already using the JVM (e.g. you're generating a Scala project), but too long of a startup time (due to all the jars it needs to download) if you're not.
- plate: Project generator written in Go. Many of the ideas for boilerplate came from this tool. Does not support non-interactive mode and has not been updated in 2+ years.
- generator-yoga: Project generator written in JavaScript. Supports templating for file copy and file contents. Interop with Yeoman. Does not support non-interactive mode.
- hugo: Static website generator written in Go. Uses Go templates. Very focused on generating websites, HTML, themes, etc, and doesn't support interactive prompts, so it's not a great fit for other types of project generation.
- jekyll: Static website generator written in Ruby. Huge community. Very focused on generating websites, HTML, themes, etc, and doesn't support interactive prompts, so it's not a great fit for other types of project generation.
- play-doc: Documentation generator used by the Play Framework that allows code snippets to be loaded from external files. Great for ensuring the code snippets in your docs are from files that are compiled and tested, but does not work as a general-purpose project generator.
License
This code is released under the Mozilla Public License Version 2.0. Please see LICENSE and NOTICE for more details.
Copyright © 2016 Gruntwork, Inc.
Documentation ¶
There is no documentation for this package.