rex

Rex is a tiny regular expression engine written in Rust. It features a parser and interpreter and supports many common RegEx features.

Build & run

cargo run -- <input file> <expression> [options]

Or, to build a binary:

cargo build
./rex <input file> <expression> [options]

Arguments can be provided in any order. For some shells (like zsh) expressions should be wrapped in quotation marks.

Testing

cargo test

Execution options

• -ng/--no-groups: Ignore matching groups (order of operations still applies).
• -b/--benchmark: Benchmark performance (results will not be printed).

Supported features

• Concatenation: abc

• Union: a|b

• Kleene closure: a*

  • One or more: a+
  • Zero or one: a?

• Grouping: (a|b)*

  • All groups are matching groups

• Escaping: a\*

  • Common escape codes: \t, \n, \v, \f, \r
  • Unicode escape codes: \u2603
    • Multi-character Unicode will compile but fail to interpret (TODO)
  • Ascii escape codes (hex or dec): \x61, \97
    • Ascii escape codes will always be valid: \x61b = ab, \971 = a1

• Charsets: [abc]

  • Negation: [^xyz]
  • Ranges: [a-zA-Z]
    • Can have a set of multiple character classes (e.g.: [\s\w])
    • Can understand when - is meant literally (e.g.: [\w-])
    • Can join characters with themselves (e.g.: [a-a])
    • Cannot join character classes (e.g.: [\w-~])
    • Cannot join characters "out of order" (e.g.: [a-A])

• Common Perl ASCII character classes:

  • .: Any Unicode character (including \n)
  • \d: digit ([0-9])
  • \D: not digit
  • \w: word ([a-zA-Z0-9_])
  • \W: not word
  • \s: whitespace ([\n-\r])
    • This range includes \f, which some versions of Perl do not
  • \S: not whitespace
  • \N: not newline ([^\n])