Tpl

Language agnostic template processor

Command line tool to process templates in a language agnostic way.

Its main use case is to be used as lightweight configuration management, able to keep local configuration files up-to-date using data from:

• environment variables
• user defined variables
• other files' content

Default settings for placeholder formats and indentation help to have valid input and output files in most cases:

$ cat template.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  selector:
    matchLabels:
      run: my-nginx
  replicas: 2
  template:
    #!-- tpl:{file:input.yaml} --#
    spec:
      containers:
      - name: my-nginx
        image: nginx
        ports:
        - containerPort: 80

$ cat input.yaml

metadata:
  labels:
    run: my-nginx

$ tpl -s template.yaml -d output.yaml

$ cat output.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  selector:
    matchLabels:
      run: my-nginx
  replicas: 2
  template:
    metadata:
      labels:
        run: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx
        ports:
        - containerPort: 80

Placeholders

Tpl allows a full placeholders configuration at run time using command line arguments.

Moreover, tpl has safe defaults as it is file type aware: if not supplied, start and end delimiters are choosen based on the file type, i.e. <!-- and --> for xml, #!-- and --# for yaml and so on...

Its default placeholders are a proper comment block, this way a template file will be always a valid file:

 <foo><!-- comment --> <!-- tpl:{var:property.key} --><foo>

foo:
  test: true
  #!-- tpl:{env:TEST} --#
  ping: pong

If the file type is unknown, the default delimiters are ${ and }.

Placeholder must be in the format:

FORMAT : [start delimiter][space]tpl:{[replacement source]}[space][end delimiter]

EXAMPLE : <!-- tpl:{ var:property.key } -->

but everything is configurable at runtime.

Using -S and -E you can set start and end placeholders' delimiters:

tpl -D \
    -s testdata/complete/template.txt \
    -d /tmp/tpl/test/out.txt \
    -S '#!--' -E '--#' \
    --var foo=hola --var config.hello=ciao

Using --placeholder-separator you can set a separator other than : for the block var:property.key.

Separator is also configurable in the template as the first non alphanumeric character in placeholder, i.e.:

<foo><!-- tpl:{|file|c:\a\path|c:\default} --></foo>

Values from env vars

Variables can be loaded from environment:

<!-- tpl:{env:THE_VAR} -->

Values from user defined vars

Variables can be declared in a properties file supplied in the option --varfile or passed as arguments from command line using --var my.property=bar.

The varfile is expected in properties format:

my.property=foo

Input file:

<info>
  <build-hash><!-- tpl:{var:build.hash} --></build-hash>
</info>

Run tpl:

tpl -s template.html \
    -d out.html \
    --var build.hash=da32da4e

Output:

<info>
  <build-hash>da32da4e</build-hash>
</info>

Values from files

Values can be loaded from full file contents (path can be absolute or relative to the template file):

<!-- tpl:{file:/path/to/file} -->

Values from file resolved at runtime

#!-- tpl:{varfile:in-[ENV].txt} --#

bin/tpl -D -s testdata/varfile/template.txt -d build/varfile.txt --var ENV=PROD

Indentation

By default, replacement contents are indented, safe for formats where indentation is important, ie yaml.

Using --no-indent this behaviour is blocked.

Write to standard output

Using --stdout content will be written to the standard out. Other logs and messages are suppressed.

tpl -D -s testdata/hello/template.txt --stdout

License

Apache 2.0 - see LICENSE file.

Copyright 2020-TODAY tpl contributors