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j2cli - Jinja2 Command-Line Tool
================================

`j2cli` is a command-line tool for templating in shell-scripts, 
leveraging the [Jinja2](http://jinja.pocoo.org/docs/) library.

Features:

* Jinja2 templating
* INI, YAML, JSON data sources supported
* Allows the use of environment variables in templates! Hello [Docker](http://www.docker.com/) :)

Inspired by [mattrobenolt/jinja2-cli](https://github.com/mattrobenolt/jinja2-cli)

## Installation

```
pip install j2cli
```

To enable the YAML support with [pyyaml](http://pyyaml.org/):

```
pip install j2cli[yaml]
```

## Tutorial

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

```jinja2
server {
  listen 80;
  server_name {{ nginx.hostname }};

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

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

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

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

```bash
$ 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`:

```jinja2
<data><name>{{ name }}</name><age>{{ age }}</age></data>
```

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

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

## Using environment variables

Even when you use yaml or json as the data source, you can always access environment variables
using the `env()` function:

```jinja2
Username: {{ login }}
Password: {{ env("APP_PASSWORD") }}
```


## 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

Or pipe it: (note that you'll have to use the "-" in this particular case):

    $ 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. Specify it explicitly when using env!

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.
* `--customize custom.py`: A Python file that implements hooks to fine-tune the j2cli behavior.
    This is fairly advanced stuff, use it only if you really need to customize the way Jinja2 is initialized.
    See [Customization](#customization) for more info.

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 dotenv 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

If you're going to pipe a dotenv file into `j2`, you'll need to use "-" as the second argument to explicitly:

    $ j2 config.j2 - < data.env

### 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:

```python
{
  '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](https://docs.docker.com/userguide/dockerlinks/)

### `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:

```jinja2
User: {{ user_login }}
Pass: {{ "USER_PASSWORD"|env }}
```

You can provide the default value:

```jinja2
Pass: {{ "USER_PASSWORD"|env("-none-") }}
```

For your convenience, it's also available as a function:

```jinja2
User: {{ user_login }}
Pass: {{ env("USER_PASSWORD") }}
```

Notice that there must be quotes around the environment variable name




Customization
=============

j2cli now allows you to customize the way the application is initialized:

* Pass additional keywords to Jinja2 environment
* Modify the context before it's used for rendering
* Register custom filters and tests

This is done through *hooks* that you implement in a customization file in Python language.
Just plain functions at the module level.

The following hooks are available:

* `j2_environment_params() -> dict`: returns a `dict` of additional parameters for
    [Jinja2 Environment](http://jinja.pocoo.org/docs/2.10/api/#jinja2.Environment).
* `j2_environment(env: Environment) -> Environment`: lets you customize the `Environment` object.
* `alter_context(context: dict) -> dict`: lets you modify the context variables that are going to be
    used for template rendering. You can do all sorts of pre-processing here.
* `extra_filters() -> dict`: returns a `dict` with extra filters for Jinja2
* `extra_tests() -> dict`: returns a `dict` with extra tests for Jinja2

All of them are optional.

The example customization.py file for your reference:

```python
# 
# Example customize.py file for j2cli
# Contains potional hooks that modify the way j2cli is initialized


def j2_environment_params():
    """ Extra parameters for the Jinja2 Environment """
    # Jinja2 Environment configuration
    # http://jinja.pocoo.org/docs/2.10/api/#jinja2.Environment
    return dict(
        # Just some examples

        # Change block start/end strings
        block_start_string='<%',
        block_end_string='%>',
        # Change variable strings
        variable_start_string='<<',
        variable_end_string='>>',
        # Remove whitespace around blocks
        trim_blocks=True,
        lstrip_blocks=True,
        # Enable line statements:
        # http://jinja.pocoo.org/docs/2.10/templates/#line-statements
        line_statement_prefix='#',
        # Keep \n at the end of a file
        keep_trailing_newline=True,
        # Enable custom extensions
        # http://jinja.pocoo.org/docs/2.10/extensions/#jinja-extensions
        extensions=('jinja2.ext.i18n',),
    )


def j2_environment(env):
    """ Modify Jinja2 environment

    :param env: jinja2.environment.Environment
    :rtype: jinja2.environment.Environment
    """
    env.globals.update(
        my_function=lambda v: 'my function says "{}"'.format(v)
    )
    return env


def alter_context(context):
    """ Modify the context and return it """
    # An extra variable
    context['ADD'] = '127'
    return context


def extra_filters():
    """ Declare some custom filters.

        Returns: dict(name = function)
    """
    return dict(
        # Example: {{ var | parentheses }}
        parentheses=lambda t: '(' + t + ')',
    )


def extra_tests():
    """ Declare some custom tests

        Returns: dict(name = function)
    """
    return dict(
        # Example: {% if a|int is custom_odd %}odd{% endif %}
        custom_odd=lambda n: True if (n % 2) else False
    )

# 

```