Crate envfmt 

Formats strings by expanding variables, similar to shell expansion.

This crate provides a simple and efficient way to substitute variables in a string, using either the process environment or a custom context like a HashMap.

The main entry points are the format() and format_with() functions.

Syntax

The formatting syntax is designed to be familiar to users of Unix shells.

• $VAR Simple variables

  • A variable name starts with an alphabetic character or an underscore, followed by any number of alphanumeric characters or underscores.
  • The expansion is greedy, meaning it will match the longest possible valid variable name.

• ${VAR} Braced variables

  • This syntax is useful for separating a variable name from subsequent characters.

• ${VAR:-default} Default values

  • If VAR is not found in the context, the default value is used instead.
  • If VAR is present in the context, even if its value is an empty string, the default is not used. This matches standard shell behavior.

• $$ Escaping

  • To include a literal dollar sign in the output, use $$.

Examples

Using environment variables:

let formatted = envfmt::format("This package is $CARGO_PKG_NAME.").unwrap();
assert_eq!(formatted, "This package is envfmt.");

Using a custom context:

use std::collections::HashMap;

let mut context = HashMap::new();
context.insert("thing", "world");

let input = "Hello, ${thing}!";
let result = envfmt::format_with(input, &context).unwrap();

assert_eq!(result, "Hello, world!");

Enums

Error

Represents errors that can occur during formatting.

Traits

Context

A trait for providing values for variable expansion.

Functions

format

Formats a string by expanding variables from the process environment.

format_with

Formats a string by expanding variables from a given context.