t2d / j2cli

Jinja2 Command-Line Tool, reworked

j2cli - Jinja2 Command-Line Tool

j2cli is a command-line tool for templating in shell-scripts, leveraging the Jinja2 library.

Features:

• Jinja2 templating
• INI, YAML, JSON data sources supported
• Allows the use of environment variables in templates! Hello Docker :)

Inspired by mattrobenolt/jinja2-cli

Installation

pip install j2cli

To enable the YAML support with pyyaml:

pip install j2cli[yaml]

Tutorial

Suppose, you want to have an nginx configuration file template, nginx.j2:

server {
  listen 80;
  server_name {{ nginx.hostname }};

  root {{ nginx.webroot }};
  index index.htm;
}

And you have a JSON file with the data, nginx.json:

{
    "nginx":{
        "hostname": "localhost",
        "webroot": "/var/www/project"
    }
}

This is how you render it into a working configuration file:

$ j2 -f json nginx.j2 nginx.json > nginx.conf

The output is saved to nginx.conf:

server {
  listen 80;
  server_name localhost;

  root /var/www/project;
  index index.htm;
}

Alternatively, you can use the -o nginx.conf option.

Tutorial with environment variables

Suppose, you have a very simple template, person.xml:

<data><name>{{ name }}</name><age>{{ age }}</age></data>

What is the easiest way to use j2 here? Use environment variables in your bash script:

$ export name=Andrew
$ export age=31
$ j2 /tmp/person.xml
<data><name>Andrew</name><age>31</age></data>

Usage

Compile a template using INI-file data source:

$ j2 config.j2 data.ini

Compile using JSON data source:

$ j2 config.j2 data.json

Compile using YAML data source (requires PyYAML):

$ j2 config.j2 data.yaml

Compile using JSON data on stdin:

$ curl http://example.com/service.json | j2 --format=json config.j2

Compile using environment variables (hello Docker!):

$ j2 config.j2

Or even read environment variables from a file:

$ j2 --format=env config.j2 data.env

Reference

j2 accepts the following arguments:

• template: Jinja2 template file to render
• data: (optional) path to the data used for rendering. The default is -: use stdin

Options:

• --format, -f: format for the data file. The default is ?: guess from file extension.

• --import-env VAR, -e EVAR: import all environment variables into the template as VAR. To import environment variables into the global scope, give it an empty string: --import-env=. (This will overwrite any existing variables!)

• -o outfile: Write rendered template to a file

• --undefined: Allow undefined variables to be used in templates (no error will be raised)

• --filters filters.py: Load custom Jinja2 filters and tests from a Python file. Will load all top-level functions and register them as filters. This option can be used multiple times to import several files.

• --tests tests.py: Load custom Jinja2 filters and tests from a Python file.

There is some special behavior with environment variables:

• When data is not provided (data is -), --format defaults to env and thus reads environment variables
• When --format=env, it can read a special "environment variables" file made like this: env > /tmp/file.env

Formats

env

Data input from environment variables.

Render directly from the current environment variable values:

$ j2 config.j2

Or alternatively, read the values from a file:

NGINX_HOSTNAME=localhost
NGINX_WEBROOT=/var/www/project
NGINX_LOGS=/var/log/nginx/

And render with:

$ j2 config.j2 data.env
$ env | j2 --format=env config.j2.

This is especially useful with Docker to link containers together.

ini

INI data input format.

data.ini:

[nginx]
hostname=localhost
webroot=/var/www/project
logs=/var/log/nginx/

Usage:

$ j2 config.j2 data.ini
$ cat data.ini | j2 --format=ini config.j2

json

JSON data input format

data.json:

{
    "nginx":{
        "hostname": "localhost",
        "webroot": "/var/www/project",
        "logs": "/var/log/nginx/"
    }
}

Usage:

$ j2 config.j2 data.json
$ cat data.json | j2 --format=ini config.j2

yaml

YAML data input format.

data.yaml:

nginx:
  hostname: localhost
  webroot: /var/www/project
  logs: /var/log/nginx

Usage:

$ j2 config.j2 data.yml
$ cat data.yml | j2 --format=yaml config.j2

Extras

Filters

docker_link(value, format='{addr}:{port}')

Given a Docker Link environment variable value, format it into something else.

This first parses a Docker Link value like this:

DB_PORT=tcp://172.17.0.5:5432

Into a dict:

{
  'proto': 'tcp',
  'addr': '172.17.0.5',
  'port': '5432'
}

And then uses format to format it, where the default format is '{addr}:{port}'.

More info here: Docker Links

env(varname, default=None)

Use an environment variable's value inside your template.

This filter is available even when your data source is something other that the environment.

Example:

User: {{ user_login }}
Pass: {{ USER_PASSWORD|env }}

You can provide the default value:

Pass: {{ USER_PASSWORD|env("-none-") }}