# shab templating language

[![Build Status](https://travis-ci.org/zimbatm/shab.svg?branch=master)](https://travis-ci.org/zimbatm/shab)

One day, @roberth and @zimbatm were tired of manually replacing variables with
sed. What if they could just drop variables in the file and have bash do the
substitution for them? Get the full power of the bash variable expansion,
brilliant!

Thus was born the shab templating language. Minimal size, maximum power
(assuming bash is already installed).

```
$ wc -l shab
24 shab
```

**SECURITY WARNING**: only use templates that you trust! The template really does
have all the power of a shell script.

## Use cases

* Configure a minimal docker container application during boot
* Fullfill a weird sense of minimalism and humour

## Example

Input:
```
$ cat example.shab
Hello,

this is a shab templating example.

Usage: ./shab example.shab

Your hostname: $(hostname)
Your user: ${USER:-unknown}
```

Output:
```
$ shab example.shab
Hello,

this is a shab templating example.

Usage: ./shab example.shab

Your hostname: x1
Your user: zimbatm
```

## Nix

Of course you want to use this in your Nix expressions!

```
with import <nixpkgs> { overlays = [ (import ./overlay.nix) ]; };
shab.renderText
  "\${GREETING}\${TARGET:+, }\${TARGET}"
  { GREETING = "Hello"; TARGET = "world"; }
```

## Docker

Use our minimal enterprise-ready docker images with only bash and shab:

```
$ cat example.shab | docker run -i --rm zimbatm/shab
Hello,

this is a shab templating example.

Usage: ./shab example.shab

Your hostname: 706d660042c4
Your user: unknown
```

## Template format

Basically anything that bash can do.

* [Variable expansion](https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html)
* Capture program outputs with `$(...)`

## Known issues

* Shab always adds a newline to the input file. See [#15](https://github.com/zimbatm/shab/issues/15).

## Dependencies

* bash
* cat

## Related projects

* envsubst from the gettext package
* https://github.com/a8m/envsubst/ which is a go re-implementation of envsubst
* manually replacing variables with sed
* https://github.com/jirutka/esh - 160 LoC POSIX-sh and awk templating
  language
* https://github.com/dylanaraps/pure-bash-bible - a fun read about
  implementing everything in pure bash

## Credits

* The authors of the UNIX V7 shell
* Richard Stallman, GNU, and bash maintainers for their reimplementation
* Our source of inspiration, [Rube Goldberg](https://en.wikipedia.org/wiki/Rube_Goldberg)
