= tera-cli
:toc: right
:proj: tera-cli
:cmd: cmd
:lib: tera
== Intro
image::resources/logo/tera-cli-logo_256.png[width=256px, align=center]
https://github.com/Keats/tera[tera] is a template engine written in Rust and inspired by Jinja2. It allows merging some data called `context data` into a template and produces a new output. This project, `tera-cli`, is a command line for the https://github.com/Keats/tera[tera template engine].
This project is called `tera-cli` but the command installed on your system is simply `tera`.
`tera-ci` offers powerful features related to your environment variables, allowing you to control the output **both** from the context data you pass but also from the ENV variables set on your system.
== Example
Here is a basic example. For instance, you will pass data such as:
----
.data.json:
include::data/basic/basic.json[]
----
as well as a template such as:
----
.template.tmpl
include::data/basic/basic.tera[]
----
and a call such as `tera --template template.tera data.json` will produce:
----
.result
<title> Demo </title>
<ul>
<li><a href="http://example.org/alice">Alice
Alice likes red green yellow
</a></li>
<li><a href="http://example.org/bob">Bob
Bob likes orange
</a></li>
</ul>
----
The **tera** engine allows way more than the simple replacements shown above. You may check out the https://tera.netlify.app/docs[doc] for more information. To name only a few, **tera** offers the following:
- variables & expressions (you can do math...)
- comments
- control structure & loops (if, for, ...)
- filters
- formatting functions (show a file size, format a date, etc...)
- inheritance, include, etc...
- built-ins: capitalize strings, replace, trim, etc...
== Install
cargo install --git https://github.com/chevdor/tera-cli
== Hot reload
You may find it useful to watch a folder with your templates and run `tera` if a template changes. For this to work, it is recommended to
name you template as `foobar.md.tera` if your template expands into a markdown file for instance.
You may then use https://github.com/emcrisostomo/fswatch[fswatch] and watch a `templates` folder using:
```
fswatch templates -e ".*\.md$" | \
xargs -n1 -I{} \
tera --include-path templates \
--template templates/template.md.tera context.json
```
== Execute as Docker container
You can find a `tera` Docker image at `chevdor/tera`. The image is very small and should be less than 8MB.
You can test it with:
docker run --rm -it chevdor/tera --version
WARNING: The Docker image mentioned above is not yet built by the CI so you may not find the very latest version from time to time.
=== Build container image
docker build --tag tera-cli .
=== Execute `tera` from the Docker container
.Check the tera help
docker run -it --rm tera-cli --help
.Parse a template
docker run -it --rm \
--volume="$(pwd)/templates:/templates" \
--read-only \
--env=FOO=BAR \
tera-cli --template /templates/env-debug.txt --env-only --env-key env
== What can I do with that anyway ?
Well... if you have **data** and you want to format them, this tool will likely be a great companion.
- You may generate beautiful changelogs in markdown, asciidoc, restructured text, etc...
- You may generate some more human views of your data
- You may... make a blog with that...
- You may generate k8s config files....
== Features
=== Supported formats
You may pass the `context` data either as file of into *stdin*.
NOTE: Current *stdin* supports only json.
=== ENV support
There are several options related to the environment variables.
==== Enable ENV variables injection
By default, the environments variables are not merged in. You can turn this feature on with `--env`.
==== Collisions
Now that you enabled the merging of the ENV variables, it is important to understand that, in some cases, your ENV may collide with your context data. This can be convenient if you want your ENV to override the context data.
==== ENV injection priority
If you prefer the context data to overwrite the ENV, you may use `--env-first`. As a result, the ENV will be applied first to the context and your context data will be loaded afterward.
==== Collisions handling
You may perfer to consider collisions as failures. This is what `--fail-on-collision` is for. If a collision is detected, the program will exit with a status code of `1` and an appropriate message.
==== ENV only
You may also want to ONLY load ENV variables as context data. This is what `--env-only` does.
==== ENV sub key
By default, your ENV variables will be loaded at the root of the context data. For instance, the `HOME` ENV variable will be then available in your tera template as `{{ HOME }}`. As we just mentioned, collisions may be an issue. There is an easy to prevent them entirely: you may move the ENV into a sub key in the context data. This is allowed thanks to the `--env-key <name>` option. For instance, using `--env-key env` will make your `HOME` ENV variable available in the tera template as `{{ env.HOME }}`.
While the syntax is a little more verbose, paired with `--fail-on-collision`, this option allows ensuring that nothing happens in your back.
=== External files
Using the `--include` flag, the command will scan recursively for files that could be https://tera.netlify.app/docs/#include[included], used as https://tera.netlify.app/docs/#macros[macros] or for https://tera.netlify.app/docs/#inheritance[inheritance]. By default, it will scan the folder where the main template is located, unless the `--include-path` option is given.
From this repository, you can test the *include* feature with the command:
USER="[YOURNAME]" tera --template data/include/hello.txt --include --env-only
and test the *inheritance* feature with:
USER="[YOURNAME]" tera --template data/inheritance/child.txt --inherit --env-only
=== Content escaping
Passing the `-a | --escape` flag allows escaping the content.
== Usage
----
include::doc/usage.adoc[]
----