Shell-like variable substitution for strings and byte strings.

• Perform substitution in &str or in &[u8].
• Provide a custom map of variables or use environment variables.
• Short format: "Hello $name!"
• Long format: "Hello ${name}!"
• Default values: "Hello ${name:person}!"
• Recursive substitution in default values: "${XDG_CONFIG_HOME:$HOME/.config}/my-app/config.toml"
• Perform substitution on all string values in YAML data (optional, requires the yaml feature).

Variable names can consist of alphanumeric characters and underscores. They are allowed to start with numbers.

The substitute() function can be used to perform substitution on a &str. The variables can either be a HashMap or a BTreeMap.

let mut variables = HashMap::new();
variables.insert("name", "world");
assert_eq!(subst::substitute("Hello $name!", &variables)?, "Hello world!");

The variables can also be taken directly from the environment with the Env map.

assert_eq!(
  subst::substitute("$XDG_CONFIG_HOME/my-app/config.toml", &subst::Env)?,
  "/home/user/.config/my-app/config.toml",
);

Substitution can also be done on byte strings using the substitute_bytes() function.

let mut variables = HashMap::new();
variables.insert("name", b"world");
assert_eq!(subst::substitute_bytes(b"Hello $name!", &variables)?, b"Hello world!");