A simple templating utility, akin to envsubst, but using Handlebars for more complex logic.
Environment variables are used as the data input to a Handlebars template:
$ export NAME=world
$ echo "Hello {{NAME}}" | envhandlebars
Hello world
This is particularly useful for dynamic configuration files in Docker containers and other 12-Factor applications.
$ npm install -g envhandlebars
Redirect a Mustache template file into stdin of envhandlebars and redirect the rendered stdout to a file:
Usage:
envhandlebars [options] < templatefile > renderedfile
Options:
--array-var-prefix="PRE_" process arrays only for vars with the specified prefix [Default: all]
--no-arrays disable variable name array processing
-h, --help print usage information
Mustache conditionals can be used as is...
Template:
{{#if WORLD}}Hello {{WORLD}}{{/if}}!
Env vars:
WORLD=worldOutput:
Hello world!
See the if block helper docs page for more information.
Mustache iterators require using a special environment variable naming convention...
Array of strings
Template:
{{#each PEOPLE}}{{this}}{{#unless @last}}, {{/unless}}{{/each}}!
Env vars:
# Convention: {VARNAME}_{INDEX}
PEOPLE_0=Chris
PEOPLE_1=John
PEOPLE_2=ShayneOutput:
Chris, John, Shayne!
Array of objects
Template:
{{#each PEOPLE}}{{FIRST}} {{LAST}}{{#unless @last}}, {{/unless}}{{/each}}!
Env vars:
# Convention: {VARNAME}_{INDEX}_{PROPERTY}
PEOPLE_0_FIRST=Chris
PEOPLE_0_LAST=Martin
PEOPLE_1_FIRST=John
PEOPLE_1_LAST=Papa
PEOPLE_2_FIRST=Shayne
PEOPLE_2_LAST=BoyerOutput:
Chris Martin, John Papa, Shayne Boyer!
See the each block helper docs page for more information.
NOTE:
Some environments may have variables that conflict with this convention.
Use the --array-var-prefix=FOO_ option to enable iterators only for variables that start with FOO_.
Alternatively, iterator parsing can be completely disabled with the --no-arrays option.
To generate configuration dynamically within a docker container, envhandlebars can be used before the main process starts. It can be done in the CMD or within a wrapper script.
Here is an example docker-compose.yml for a custom nginx container:
nginx:
build: .
volumes:
- ./mysite.template:/etc/nginx/conf.d/mysite.template
ports:
- "8080:80"
environment:
- NGINX_HOST=foobar.com
- NGINX_PORT=80
command: /bin/bash -c "envhandlebars < /etc/nginx/conf.d/mysite.template > /etc/nginx/conf.d/default.conf && nginx -g 'daemon off;'"
The mysite.template file may then contain variable references like this:
listen {{NGINX_PORT}};
You just need to make sure to install Node.js and envhandlebars (via npm) within your custom Dockerfile.
For debian-based images:
RUN apt-get update && apt-get install -y nodejs && npm i -g envhandlebars
For alpine-based images:
RUN apk add --update nodejs && npm i -g envhandlebars
(New in v1.3.0+)
Custom Mustache helpers and partials can be implemented by extending the envhandlebars module with your own Node.js wrapper script:
#!/usr/bin/env node
// Script: `myenvhandlebars`
'use strict';
var envhandlebars = require('envhandlebars');
// The Handlebars context is passed into this function
// for registering helpers, partials or other extensions.
function extendHandlebars(Handlebars) {
Handlebars.registerHelper('fullName', function(first, last) {
return last + ', ' + first;
});
}
envhandlebars({
extendHandlebars: extendHandlebars
});See the custom helpers docs page for more information.
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