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

/
/
x

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#"(?x)(?(DEFINE) # Note that everything is atomic, JSON does not need backtracking if it's valid # and this prevents catastrophic backtracking (?<json>(?>\s*(?&object)\s*|\s*(?&array)\s*)) (?<object>(?>\{\s*(?>(?&pair)(?>\s*,\s*(?&pair))*)?\s*\})) (?<pair>(?>(?&STRING)\s*:\s*(?&value))) (?<array>(?>\[\s*(?>(?&value)(?>\s*,\s*(?&value))*)?\s*\])) (?<value>(?>true|false|null|(?&STRING)|(?&NUMBER)|(?&object)|(?&array))) (?<STRING>(?>"(?>\\(?>["\\\/bfnrt]|u[a-fA-F0-9]{4})|[^"\\\0-\x1F\x7F]+)*")) (?<NUMBER>(?>-?(?>0|[1-9][0-9]*)(?>\.[0-9]+)?(?>[eE][+-]?[0-9]+)?)) ) \A(?&json)\z"#).unwrap(); let string = "[ \"JSON Test Pattern pass1\", {\"object with 1 member\":[\"array with 1 element\"]}, {}, [], -42, true, false, null, { \"integer\": 1234567890, \"real\": -9876.543210, \"e\": 0.123456789e-12, \"E\": 1.234567890E+34, \"\": 23456789012E66, \"zero\": 0, \"one\": 1, \"space\": \" \", \"quote\": \"\\\"\", \"backslash\": \"\\\\\", \"controls\": \"\\b\\f\\n\\r\\t\", \"slash\": \"/ & \\/\", \"alpha\": \"abcdefghijklmnopqrstuvwyz\", \"ALPHA\": \"ABCDEFGHIJKLMNOPQRSTUVWYZ\", \"digit\": \"0123456789\", \"0123456789\": \"digit\", \"special\": \"`1~!@#$%^&*()_+-={':[,]}|;.</>?\", \"hex\": \"\\u0123\\u4567\\u89AB\\uCDEF\\uabcd\\uef4A\", \"true\": true, \"false\": false, \"null\": null, \"array\":[ ], \"object\":{ }, \"address\": \"50 St. James Street\", \"url\": \"http://www.JSON.org/\", \"comment\": \"// /* <!-- --\", \"# -- --> */\": \" \", \" s p a c e d \" :[1,2 , 3 , 4 , 5 , 6 ,7 ],\"compact\":[1,2,3,4,5,6,7], \"jsontext\": \"{\\\"object with 1 member\\\":[\\\"array with 1 element\\\"]}\", \"quotes\": \"&#34; \\u0022 %22 0x22 034 &#x22;\", \"\\/\\\\\\\"\\uCAFE\\uBABE\\uAB98\\uFCDE\\ubcda\\uef4A\\b\\f\\n\\r\\t`1~!@#$%^&*()_+-=[]{}|;:',./<>?\" : \"A key can be any string\" }, 0.5 ,98.6 , 99.44 , 1066, 1e1, 0.1e1, 1e-1, 1e00,2e+00,2e-00 ,\"rosebud\"]"; // 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/