Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
mx

Test String

Code Generator

Language

Generated Code

// include the latest version of the regex crate in your Cargo.toml extern crate regex; use regex::Regex; fn main() { let regex = Regex::new(r"(?mx)(?:\s*from\s(?:(?:([^\(\n]*?)\s)|(\[[^\]]*\]))?(?:\((?:(?:((?!HELO|EHLO)[^\s]*)|(?:(?:EHLO)|(?:HELO)))?(?:[\s\w\.]*(?:(?:\[([^\]]*)\])|([^\)\s]*))\))))?(?:\{.*\})?)? \s*(?:(?:client\s)?[\(\{\[]+([^\)\}\]]*)[\)\}\]]+\;?(?:\{.*\})?)? (?:[\s\n]*) (?:\s*(?:by(?:(?:.*?)(?:\;|(?:[\r\n]+))))(?!.*with))? (?:\s*(?:by\s[^\;]*\)?)(?=.*with)\s*)? (?:with\s*(?:((?:[^\n;]*))(?:.*\;)?))? (?:[\s\n]*)? (?:\(?envelope-from\s*([^\n]*)\;?\)?)? (?:\s*id[^;]*\;?)? (?:[\s\n]*)? (?:for\s([^\;]*)\;)? (?:[\s\n]*)? (?:\(.*\)\;)?(?:[\s\n])? ([^\(]+)? (?:\(?envelope-from\s*([^\n]*)\;?\)?)?").unwrap(); let string = "from qzienfhr ([182.109.196.197]) by mail.oucu.edu.eg with SMTP (Code-Crafters Ability Mail Server 2012); Mon, 03 Dec 2018 12:42:56 +0200"; // result will be a tuple containing the start and end indices for the first match in the string let result = regex.captures(string); let (start, end) = match result { Some((s, e)) => (s, e), None => { // ... } }; println!("{}", &string[start, end]); }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Rust, please visit: https://docs.rs/regex/latest/regex/