envtpl

envtpl is envtpl in Crystal

envtpl renders Crinja templates on the command line using environment variables.

Installation

Grab the latest binary from the releases page and run it :)

Usage

Usage: envtpl [arguments]
    -i FILE, --in=FILE               Specifies the input file (STDIN by default)
    -o FILE, --out=FILE              Specifies the output file (STDOUT by default)
    -s, --strict                     Fail instead of rendering an empty string for an undefined variable
    -v, --version                    Show version
    -h, --help                       Show this help

The template is rendered verbatim: whether it goes to STDOUT or to --out, the output is byte for byte the same, trailing newline included.

Examples

Reading a variable

Any environment variable is available under its own name:

$ echo "Hello: {{ SHELL }}" | envtpl
Hello: /bin/bash

The env() function does the same and also works for names that are not valid template identifiers ({{ MY-VAR }} does not parse, {{ env('MY-VAR') }} does):

$ echo "Hello: {{ env('SHELL') }}" | envtpl
Hello: /bin/bash

Called with several names, it returns a hash restricted to them, skipping the ones that are not set:

$ echo "Hello: {{ env('SHELL', 'USER') }}" | envtpl
Hello: {'SHELL' => '/bin/bash', 'USER' => 'nicolas'}

Called with no argument at all, it returns the whole environment. Mind that this includes every secret the process was given:

$ echo "{{ env() }}" | envtpl
{'SHELL' => '/bin/bash', 'USER' => 'nicolas', ...}

Missing variables

An undefined variable renders as an empty string, so a typo silently produces an empty value:

$ echo "[{{ NO_SUCH_VAR }}]" | envtpl
[]

Use default= to make the fallback explicit:

$ echo "{{ env('NO_SUCH_VAR', default='fallback') }}" | envtpl
fallback

…or --strict to turn the whole thing into an error. default() and is defined keep working under --strict; only rendering an undefined variable fails:

$ echo "[{{ NO_SUCH_VAR }}]" | envtpl --strict
Crinja::UndefinedError: NO_SUCH_VAR is undefined.
template: <stdin>:1:2 .. 1:19

 1 | [{{ NO_SUCH_VAR }}]
 X |  ^~~~~~~~~~~~~~~~~
$ echo $?
1

The json filter

Serialises any value as JSON, indented by two spaces unless told otherwise:

$ echo "{{ env('SHELL', 'USER') | json }}" | envtpl
{
  "SHELL": "/bin/bash",
  "USER": "nicolas"
}

$ echo "{{ env('SHELL', 'USER') | json(indent=4) }}" | envtpl
{
    "SHELL": "/bin/bash",
    "USER": "nicolas"
}

A note on template trust

Templates are executable input: {% include 'other.j2' %} reads any file under the current working directory (absolute paths and ../ traversal are refused). Render templates you trust.

Contributing

1. Fork it (https://github.com/jbox-web/envtpl.cr/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Nicolas Rodriguez - creator and maintainer

Similar Tools

• https://github.com/envtpl/envtpl (Python)
• https://github.com/subfuzion/envtpl (Go)
• https://github.com/mattrobenolt/envtpl (Go)
• https://github.com/arschles/envtpl (Go)
• https://github.com/niquola/envtpl (Rust)