Created
January 18, 2020 15:52
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shellexpand-combine.rs PoC
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| use std::borrow::Cow; | |
| use std::env; | |
| use combine::error::ParseError; | |
| use combine::parser::char::{alpha_num, char, letter, string}; | |
| use combine::parser::combinator::recognize; | |
| use combine::stream::Stream; | |
| use combine::{choice, easy, many1, optional, parser, satisfy, skip_many, EasyParser, Parser}; | |
| #[derive(Debug, PartialEq)] | |
| struct Var { | |
| name: String, | |
| default: Option<Box<Value>>, | |
| } | |
| #[derive(Debug, PartialEq)] | |
| enum Value { | |
| Var(Var), | |
| String(String), | |
| } | |
| fn value_var(name: String, default: Option<Box<Value>>) -> Value { | |
| Value::Var(Var { name, default }) | |
| } | |
| #[derive(Debug)] | |
| struct ShellExpand { | |
| values: Vec<Value>, | |
| } | |
| fn varname<Input>() -> impl Parser<Input, Output = String> | |
| where | |
| Input: Stream<Token = char>, | |
| Input::Error: ParseError<Input::Token, Input::Range, Input::Position>, | |
| { | |
| recognize((letter(), skip_many(alpha_num()))) | |
| } | |
| fn variable<Input>() -> impl Parser<Input, Output = Value> | |
| where | |
| Input: Stream<Token = char>, | |
| Input::Error: ParseError<Input::Token, Input::Range, Input::Position>, | |
| { | |
| let bracet_var = ( | |
| // name | |
| varname(), | |
| // default | |
| optional(string(":-").with(shell_value_strict())), | |
| ) | |
| .skip(char('}')) | |
| .map(|(name, default)| value_var(name, default.map(|value| Box::new(value)))); | |
| let variable = ( | |
| char('$'), | |
| optional(choice(( | |
| char('{').with(bracet_var), | |
| varname().map(|name| value_var(name, None)), | |
| ))), | |
| ) | |
| .map(|(_, value)| match value { | |
| None => Value::String("$".into()), | |
| Some(value) => value, | |
| }); | |
| variable | |
| } | |
| parser! { | |
| fn shell_value[Input]()(Input) -> Value | |
| where [Input: Stream<Token = char>] | |
| { | |
| let shell_string = many1(satisfy(|c| c != '$')).map(Value::String); | |
| choice((variable(), shell_string)) | |
| } | |
| } | |
| parser! { | |
| fn shell_value_strict[Input]()(Input) -> Value | |
| where [Input: Stream<Token = char>] | |
| { | |
| let shell_string = many1(satisfy(|c| c != '$' && c != '}')).map(Value::String); | |
| choice((variable(), shell_string)) | |
| } | |
| } | |
| fn parse_shell<Input>() -> impl Parser<Input, Output = Vec<Value>> | |
| where | |
| Input: Stream<Token = char>, | |
| Input::Error: ParseError<Input::Token, Input::Range, Input::Position>, | |
| { | |
| many1(shell_value()) | |
| } | |
| fn expand<'a>(value: &'a Value) -> Cow<'a, str> { | |
| match value { | |
| Value::String(string) => Cow::Borrowed(string), | |
| Value::Var(var) => match env::var(&var.name) { | |
| Ok(value) => Cow::Owned(value), | |
| Err(_) => match &var.default { | |
| Some(env) => expand(&env), | |
| None => Cow::Borrowed(""), | |
| }, | |
| }, | |
| } | |
| } | |
| fn parse(input: &str) -> String { | |
| let shell_values: Result<(Vec<Value>, &str), easy::ParseError<&str>> = | |
| parse_shell().easy_parse(input); | |
| let result = shell_values.map_err(|e| e.map_position(|p| p.translate_position(input))); | |
| result.unwrap().0.iter().map(expand).collect() | |
| } | |
| fn main() { | |
| let input = "$UNSET Test: :- $}$1 ${UNSET:-$} ${UNSET:-42} $HOME/.config/ ${UNSET:-${UNSET2:-$USER}}"; | |
| println!("Input: {}", input); | |
| println!("Result: {}", parse(input)); | |
| // Output: | |
| // Input: $UNSET Test: :- $}$1 ${UNSET:-$} ${UNSET:-42} $HOME/.config/ ${UNSET:-${UNSET2:-$USER}} | |
| // Result: Test: :- $}$1 $ 42 /home/roger/.config/ roger | |
| } |
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