shellish_parse

This is a Rust crate to do "command line parsing". No, I'm not talking about parsing command line arguments that were passed to your program; for that purpose, I recommend the excellent Clap crate (with features wrap_help and derive enabled). What this crate does is take a line of text and parse it like a command line. In other words, it parses shellish.

This is useful if you're implementing any kind of interactive system where a user needs to be able to input commands.

Usage

Add shellish_parse to your Cargo.toml:

shellish_parse = "2.1"

Use shellish_parse::parse to parse some shellish:

let line = "Hello World";
assert_eq!(shellish_parse::parse(line, false).unwrap(), &[
    "Hello", "World"
]);

The first parameter, a &str, is the line to parse. The second parameter, a bool, is whether an unrecognized escape sequence should be an error:

let line = r#"In\mvalid"#; // note: raw string
assert_eq!(shellish_parse::parse(line, false).unwrap(), &[
    "In�valid"
]);
assert_eq!(shellish_parse::parse(line, true).unwrap_err(),
    shellish_parse::ParseError::UnrecognizedEscape("\\m".to_string()));

You may want to use an alias to make it more convenient, if you're using it in a lot of places:

use shellish_parse::parse as parse_shellish;
let line = "Hello World";
assert_eq!(parse_shellish(line, false).unwrap(), &[
    "Hello", "World"
]);

Regular parse is great and everything, but sometimes you want to be able to chain multiple commands on the same line. That's where multiparse comes in:

let line = "Hello World; How are you?";
assert_eq!(shellish_parse::multiparse(line, true, &[";"]).unwrap(), &[
    (vec!["Hello".to_string(), "World".to_string()], Some(0)),
    (vec!["How".to_string(), "are".to_string(), "you?".to_string()], None),
]);

(Since it returns a vec of tuples, it's rather awkward to phrase in tests.)

You pass the separators you want to use. A single semicolon is probably all you want. If you want to get really fancy, you can add arbitrarily many different separators. Each command returned comes with the index of the separator that terminated it:

let line = "test -f foo && pv foo | bar || echo no foo & echo wat";
assert_eq!(shellish_parse::multiparse(line, true, &["&&", "||", "&", "|",
                                                    ";"]).unwrap(), &[
    (vec!["test".to_string(), "-f".to_string(), "foo".to_string()], Some(0)),
    (vec!["pv".to_string(), "foo".to_string()], Some(3)),
    (vec!["bar".to_string()], Some(1)),
    (vec!["echo".to_string(), "no".to_string(), "foo".to_string()], Some(2)),
    (vec!["echo".to_string(), "wat".to_string()], None),
]);

Since the separators are checked in the order passed, put longer separators before shorter ones. If "&" preceded "&&" in the above call, "&" would always be recognized first, and "&&" would never be recognized.

Extremely shellish things, like redirection or using parentheses to group commands, are out of scope of this crate. If you want those things, you might be writing an actual shell, and not just something shellish.

Syntax

The syntax is heavily inspired by the UNIX Bourne shell. Quotation works exactly like in said shell. Backslashes can also be used for escaping (and more advanced usage, more like Rust strings than shellish). Unlike the real Bourne shell, parse_shellish contains no form of variable substitution.

Whitespace

Elements are separated by one or more whitespace characters.

let line = "Hello there!";
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "Hello", "there!",
])

Whitespace consists of spaces, tabs, or newlines. Whitespace before and after the command line is ignored. Any combination and quantity of whitespace between elements acts the same as a single space.

let line = "\tHello\n\t  there!    \n\n";
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "Hello", "there!",
])

Backslash escapes

(All example input strings in this section are given as raw strings. The backslashes and quotation marks you see in them are literal.)

You may escape any character with backslash.

Backslash followed by an ASCII letter (26 letters 'A' through 'Z' and 'a' through 'z') or digit ('0' through '9') has a special meaning.

• 'n': Newline (U+000A LINE FEED)
• 't': Tab (U+0009 CHARACTER TABULATION)
• Any other letter (and any digit) will either insert a � (U+FFFD REPLACEMENT CHARACTER) or cause a parse error, depending on the value you pass as the second parameter to parse.

let line = r#"General\t Kenobi\n"#;
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "General\t", "Kenobi\n",
])

Backslash followed by a newline followed by any number of unescaped tabs or spaces will give nothing, just like in Rust strings. (i.e. you may continue a command line onto another line by preceding the linebreak with a backslash)

let line = r#"You will die br\
              aver than most."#;
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "You", "will", "die", "braver", "than", "most."
])

Backslash followed by anything else will give that character, ignoring any special meaning it might otherwise have had.

let line = r#"Four\-score\ and\ seven \"years\" ago"#;
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "Four-score and seven", "\"years\"", "ago"
])

Future versions may add more special characters. These will only be denoted by letter(s) or digit(s). For all other characters, the handling of backslash is guaranteed not to change.

Quoting

(All example input strings in this section are given as raw strings. The backslashes and quotation marks you see in them are literal.)

You may quote parts of the command line. The quoted text will all go into the same element.

let line = r#"cp "Quotation Mark Test" "Quotation Mark Test Backup""#;
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "cp", "Quotation Mark Test", "Quotation Mark Test Backup"
])

Quoting will not create a new element on its own.

let line = r#"I Probably Should Have"Added A Space!""#;
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "I", "Probably", "Should", "HaveAdded A Space!"
])

There are two kinds of quotation. A double-quoted string will interpret backslash escapes, including \".

let line = r#"movie recommend "\"Swing it\" magistern""#;
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "movie", "recommend", "\"Swing it\" magistern"
])

A single-quoted string will not interpret backslash escapes, not even \'!

let line = r#"addendum 'and then he said "But I haven'\''t seen it, I \
just searched for '\''movies with quotes in their titles'\'' on IMDB and \
saw that it was popular"'"#;
assert_eq!(shellish_parse::parse(line, true).unwrap(), &[
    "addendum", "and then he said \"But I haven't seen it, I just \
searched for 'movies with quotes in their titles' on IMDB and saw that it \
was popular\""
])

Continuation

parse returns Err(ParseResult::...) on failure. There are three ways parsing can fail:

1. Dangling backslash: like this\
2. Unterminated string: like "this
3. Unrecognized escape sequence: like this\m

In the first two cases, parsing could succeed if there were only more input to read. So you can handle these errors by prompting for more input, adding it onto the end of the string, and trying again. The needs_continuation method of ParseResult is here to help:

// note: raw strings
let input_lines = [r#"This is not a very \"#,
                   r#"long line, so why did \"#,
                   r#"we choose to 'force "#,
                   r#"continuation'?"#];
let mut input_iter = input_lines.into_iter();
let mut buf = input_iter.next().unwrap().to_string();
let result = loop {
    match shellish_parse::parse(&buf, true) {
        Err(x) if x.needs_continuation() => {
            buf.push('\n'); // don't forget this part!
            buf.push_str(input_iter.next().unwrap())
        },
        x => break x,
    }
};
assert_eq!(result.unwrap(), &[
    "This", "is", "not", "a", "very", "long", "line,", "so", "why", "did",
    "we", "choose", "to", "force \ncontinuation?"
]);

Legalese

shellish_parse is copyright 2022, Solra Bizna, and licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the shellish_parse crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

License: MIT OR Apache-2.0