render-template

This tools allows rendering Handlebars 3.0 templates, using as context data the current environment variables or a provided data file.

Basic usage

$> render-template --help
Usage:
  render-template [OPTIONS] [template-file]

Application Options:
  -f, --data-file=DATA_FILE    Properties file containing the replacements for the template

Help Options:
  -h, --help                   Show this help message

Arguments:
  template-file:               File containing the template to render. Its contents can be also passed through stdin

The tool supports rendering templates from a file or from stdin (for convenience).

The source data is taken from the environment variables or from a data file, with properties-file format (key=value, a line for each pair). When a variable is defined both as an environment variable and in the data file, the latter will take precedence.

Examples

Render data from template file with environment variables

# Create the template
$> echo 'hello {{who}}' > template.tpl
# Render it without 'who' variable
$> render-template template.tpl
hello 
# Render it with 'who' variable defined
$> who=bitnami render-template template.tpl
hello bitnami

Render data from stdin with environment variables

$> log_file=/tmp/stout.log port=8080 pid_file=/tmp/my.pid render-template <<"EOF"
# My servide log file
log_file "{{log_file}}"

# HTTP port
port {{port}}

# My service pid file
pid_file "{{pid_file}}"
EOF

Outputs:

# My servide log file
log_file "/tmp/stout.log"

# HTTP port
port 8080

# My service pid file
pid_file "/tmp/my.pid"

Render data from stdin with data file

# write data file
$> cat > data.properties <<"EOF"
log_file=/tmp/stout.log
port=8080
pid_file=/tmp/my.pid 
EOF

$> render-template --data-file ./data.properties <<"EOF"
# My servide log file
log_file "{{log_file}}"

# HTTP port
port {{port}}

# My service pid file
pid_file "{{pid_file}}"
EOF

Outputs:

# My servide log file
log_file "/tmp/stout.log"

# HTTP port
port 8080

# My service pid file
pid_file "/tmp/my.pid"

Overriding environment variables in data file

# Lets define some environment variables
$> export name=foo
$> export company=bar
$> export year=3000

# And write a template
$> cat > data.tpl <<"EOF"
{{name}} works at {{company}}
since {{year}}
EOF

# Rendering from the environment would yield
$> render-template data.tpl
foo works at bar
since 3000

# But we can override it from a data file, either partially, to get a mix:

$> echo "name=mike" > data.properties
$> render-template --data-file data.properties data.tpl
mike works at bar
since 3000

# Or completely:

$> cat > data.properties <<"EOF"
name=mike
company=Bitnami
year=2010
EOF

$> render-template --data-file data.properties data.tpl
mike works at Bitnami
since 2010

Using helpers

The tool supports all the standard handlebars helpers: https://handlebarsjs.com/builtin_helpers.html

$> render-template <<"EOF" 
 {{#if author}}
{{firstName}} {{lastName}}
 {{else}}
Unknown Author
 {{/if}}
EOF

# Which outputs
Unknown Author

$> author=me firsName=foo lastName=bar render-template <<"EOF" 
 {{#if author}}
{{firstName}} {{lastName}}
 {{else}}
Unknown Author
 {{/if}}
EOF

# Outputs:
foo bar

In addition, it includes a few custom helpers:

json_escape

The json_escape helper converts the provided value into a valid JSON string

$> export VALUE='this is "a string", with quoting

and some line breaks'

Without the helper:

$> render-template <<<'VALUE={{VALUE}}'
VALUE=this is "a string", with quoting

and some line breaks

Using the helper:

$> render-template <<<'VALUE={{json_escape VALUE}}'
VALUE="this is \"a string\", with quoting\n\nand some line breaks"

quote

The quote helper Quotes a string

Without the helper:

$> ARG1="some arg" ARG2="some other \"arg\"" render-template <<"EOF"
ARG1={{ARG1}} ARG2={{ARG2}}
EOF
ARG1=some arg ARG2=some other "arg"

With the helper

ARG1="some arg" ARG2="some other \"arg\"" render-template <<"EOF"
ARG1={{quote ARG1}} ARG2={{quote ARG2}}
EOF
ARG1="some arg" ARG2="some other \"arg\""

or

This helper allows using the "or" logical operation over two values (a value will be true if not empty)

To render a block when either "firstName" or "lastName" values ar not empty:

$> cat > data.tpl <<"EOF" 
{{#if (or firstName lastName)}}
{{firstName}} {{lastName}}
{{else}}
Unknown Author
{{/if}}
EOF

$>render-template data.tpl
Unknown Author

$> firstName=foo render-template data.tpl
foo

$> lastName=bar render-template data.tpl
 bar
 
$> firstName=foo lastName=bar render-template data.tpl
foo bar

This helper can also be used to provide defaults for your template variables:

# No value provided, so we fallback to the second "or" argument
$> render-template <<<'VALUE={{or ENV_VALUE "default value"}}'
VALUE=default value

# ENV_VALUE is defined, so we take it
$> ENV_VALUE="customized value" render-template <<<'VALUE={{or ENV_VALUE "default value"}}'
VALUE=customized value