sigil

Sigil

Standalone string interpolator and template processor

echo '${name} is{{ range seq ${count:-3} }} cool{{ end }}!' | sigil -p name=Sigil

Sigil is cool cool cool!

Sigil is a command line tool for template processing and POSIX-compliant variable expansion. It was created for configuration templating, but can be used for any text processing.

Getting Sigil

curl -L "https://github.com/gliderlabs/sigil/releases/download/v0.10.0/gliderlabs-sigil_0.10.0_$(uname -sm|tr \  _).tgz" \
    | tar -zxC /usr/local/bin

Other releases can be downloaded from Github Releases.

Using Sigil

Template text can be provided via STDIN or from a file if provided with the -f flag. Any other arguments are key-values in the form <key>=<value>. They are used as variables.

• echo 'Hello, $name' | sigil -p name=Jeff
• sigil -p -f config.tmpl var1=foo "var2=Hello world"

Variables

POSIX style

There are two forms of variable syntax in Sigil. The first is POSIX style, which among other features allows default values or enforces required values:

• $variable - normal POSIX style
• ${variable:-"default"} - expansion with default value
• ${variable:?} - fails when not set

Environment variables are also available as POSIX style variables. This makes Sigil great for quick and simple string interpolation.

Template style

The other syntax to use variables is consistent with the rest of the templating syntax. It uses {{ and }} to define template expressions. Variable expansion in this form is simply used as:

• {{ $variable }}

You can do much more with this syntax, such as modifier pipelines. All of which is explained below.

Custom Delimiters

Sometimes you want to use sigil to generate text, which uses golang templating itself. For example if you want to generate packer configuration your template might contain a lot of {{ and }}.

Instead of replacing all {{ with {{“{{”}}, you can change the delimiters, by setting the SIGIL_DELIMS environment variable. It is the left and right delimiter strings, separated by a coma.

SIGIL_DELIMS={{{,}}}  sigil -i 'hello {{{ $name }}}' name=packer

In-place editing

Use the --in-place flag with -f to write the rendered output back to the template file, similar to sed -i:

sigil --in-place -f config.tmpl var1=foo var2=bar

This safely replaces the file using an atomic write (temp file + rename), so the original file is preserved if template processing fails. File permissions are retained.

Note: --in-place requires the -f flag. It cannot be used with -i (inline) or stdin input.

Variables from files

Use the --vars-file (or -V) flag to load variables from a file instead of passing them all as command-line arguments. The flag can be specified multiple times; files are merged in order, and CLI key=value arguments override any file-sourced variables.

The file format is auto-detected by extension:

• .json - parsed as a JSON object
• .yaml / .yml - parsed as a YAML mapping
• .env or any other extension - parsed as key=value lines

JSON example (vars.json)

{
  "name": "Jeff",
  "greeting": "Hello",
  "port": 8080
}

YAML example (vars.yaml)

name: Jeff
greeting: Hello
port: 8080

Env example (vars.env)

# Database config
DB_HOST=localhost
DB_PORT=5432
DB_NAME="my_database"
export APP_ENV='production'

Usage

# JSON vars file
sigil -f config.tmpl -V vars.json

# YAML vars file
sigil -f config.tmpl -V vars.yaml

# env-style vars file
sigil -f config.tmpl -V vars.env

# Multiple files, later overrides earlier
sigil -f config.tmpl -V defaults.yaml -V overrides.json

# CLI args override file vars
sigil -f config.tmpl -V vars.json name=override

Functions

There are a number of builtin functions that can be used as modifiers, conditional tests, expansion data sources, and more. There are two references for functions available:

• Sigil builtins
• Go template builtins

Here are a few examples:

• {{ $variable | capitalize }}
• {{ $variable | default "fallback" }} - use fallback when variable is not provided or empty
• {{ include "file.tmpl" "var1=foo" "var2=bar" }}
• {{ file "example.txt" | replace "old" "new" }}
• {{ json "file.json" | pointer "/Widgets/0/Name" }}

Conditionals

• {{ if expr }} true {{ end }}
• {{ if expr }} true {{ else }} false {{ end }}
• {{ if expr }} true {{ else if expr }} also true {{ end }}

Loops / Iteration

• {{ range expr }} element: {{.}} {{ end }}
• {{ range expr }} elements {{ else }} no elements {{ end }}

Full Syntax

Lots more is possible with this template syntax. Sigil is based on Go's text/template package. You can read full documentation there.

License

BSD