Regular Expressions 101

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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
Processing...

Test String

Substitution
Processing...

Code Generator

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#"(?m)^(?:(?:(?&V_Obj)|(?&V_Ary))|(?<Invalid>(?&Er_Obj)|(?&Er_Ary))(*SKIP)(*FAIL))(?(DEFINE)(?<Sep_Ary>(?:,(?!\s*[}\]])|(?=\s*[\]])))(?<Sep_Obj>(?:,(?!\s*[}\]])|(?=\s*[}])))(?<Er_Obj>(?>{(?:\s*(?&Str)(?:\s*:(?:\s*(?:(?&Er_Value)|(?<Er_Ary>\[(?:\s*(?:(?&Er_Value)|(?&Er_Ary)|(?&Er_Obj))(?:\s*(?&Sep_Ary)|(*ACCEPT)))*(?:\s*\]|(*ACCEPT)))|(?&Er_Obj))(?:\s*(?&Sep_Obj)|(*ACCEPT))|(*ACCEPT))|(*ACCEPT)))*(?:\s*}|(*ACCEPT))))(?<Er_Value>(?>(?&Numb)|(?>true|false|null)|(?&Str)))(?<Str>(?>"[^\\"]*(?:\\[\s\S][^\\"]*)*"))(?<Numb>(?>[+-]?(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][+-]?\d+)?|(?:[eE][+-]?\d+)))(?<V_KeyVal>(?>\s*(?&Str)\s*:\s*(?&V_Value)\s*))(?<V_Value>(?>(?&Numb)|(?>true|false|null)|(?&Str)|(?&V_Obj)|(?&V_Ary)))(?<V_Ary>\[(?>\s*(?&V_Value)\s*(?&Sep_Ary))*\s*\])(?<V_Obj>{(?>\s*(?&V_KeyVal)\s*(?&Sep_Obj))*\s*}))"#).unwrap(); let string = " ================================ Valid JSON : ================================= 1. Nested Objects and Arrays (Company Structure) This example demonstrates a company structure with departments, each containing a list of employees. { \"company\": \"Global Solutions Inc.\", \"headquarters\": { \"city\": \"New York\", \"state\": \"NY\", \"zip\": \"10001\" }, \"departments\": [ { \"name\": \"Engineering\", \"manager\": { \"id\": \"ENG001\", \"firstName\": \"Alice\", \"lastName\": \"Johnson\" }, \"employees\": [ { \"id\": \"EMP001\", \"firstName\": \"Bob\", \"lastName\": \"Williams\", \"position\": \"Software Engineer\", \"skills\": [\"Python\", \"Java\", \"SQL\"] }, { \"id\": \"EMP002\", \"firstName\": \"Charlie\", \"lastName\": \"Davis\", \"position\": \"DevOps Engineer\", \"skills\": [\"AWS\", \"Docker\", \"Kubernetes\"] } ] }, { \"name\": \"Marketing\", \"manager\": { \"id\": \"MKT001\", \"firstName\": \"David\", \"lastName\": \"Miller\" }, \"employees\": [ { \"id\": \"EMP003\", \"firstName\": \"Eve\", \"lastName\": \"Taylor\", \"position\": \"Marketing Specialist\", \"skills\": [\"SEO\", \"Content Creation\"] } ] } ], \"projects\": [ { \"projectId\": \"PROJ101\", \"projectName\": \"New Product Launch\", \"status\": \"In Progress\", \"teamMembers\": [\"EMP001\", \"EMP003\"] } ] } 2. GeoJSON Feature Collection (Geospatial Data) This example uses the GeoJSON standard to represent a collection of geographic features. { \"type\": \"FeatureCollection\", \"features\": [ { \"type\": \"Feature\", \"properties\": { \"name\": \"Eiffel Tower\", \"country\": \"France\", \"city\": \"Paris\" }, \"geometry\": { \"type\": \"Point\", \"coordinates\": [2.2945, 48.8584] } }, { \"type\": \"Feature\", \"properties\": { \"name\": \"Central Park\", \"country\": \"USA\", \"city\": \"New York\" }, \"geometry\": { \"type\": \"Polygon\", \"coordinates\": [ [ [-73.981, 40.768], [-73.958, 40.796], [-73.949, 40.793], [-73.981, 40.768] ] ] } } ] } 3. Product Catalog with Variations (E-commerce) This JSON structure represents a product catalog with various product details and variations. { \"catalogId\": \"CAT001\", \"products\": [ { \"productId\": \"PROD001\", \"name\": \"T-Shirt\", \"description\": \"Comfortable cotton t-shirt.\", \"price\": 19.99, \"availableSizes\": [\"S\", \"M\", \"L\", \"XL\"], \"colors\": [ { \"name\": \"Red\", \"hexCode\": \"#FF0000\", \"stock\": { \"S\": 10, \"M\": 15, \"L\": 8, \"XL\": 5 } }, { \"name\": \"Blue\", \"hexCode\": \"#0000FF\", \"stock\": { \"S\": 12, \"M\": 20, \"L\": 10, \"XL\": 7 } } ], \"reviews\": [ { \"userId\": \"USER001\", \"rating\": 5, \"comment\": \"Great quality and fit!\" }, { \"userId\": \"USER002\", \"rating\": 4, \"comment\": \"Good t-shirt, a bit pricey.\" } ] }, { \"productId\": \"PROD002\", \"name\": \"Jeans\", \"description\": \"Classic denim jeans.\", \"price\": 49.99, \"availableSizes\": [\"28\", \"30\", \"32\", \"34\"], \"colors\": [ { \"name\": \"Indigo\", \"hexCode\": \"#4B0082\", \"stock\": { \"28\": 7, \"30\": 10, \"32\": 12, \"34\": 8 } } ] } ] } ========================= Invalid JSON : ========================= These examples illustrate various ways in which a JSON file can be considered invalid according to the JSON specification. Developers often encounter these types of errors during data serialization or parsing. ----------------- 1. Missing Double Quotes around Keys: Code { name: \"Alice\", \"age\": 30, \"city\": \"New York\" } Invalidity: The key name is not enclosed in double quotes, which is a requirement in JSON. ----------------- 2. Trailing Commas in Objects or Arrays: Code { \"item1\": \"value1\", \"item2\": \"value2\", } Invalidity: There is a trailing comma after the last key-value pair in the object. Code [ \"element1\", \"element2\", ] Invalidity: There is a trailing comma after the last element in the array. ----------------- 3. Incorrect Data Types or Values: Code { \"product\": \"Laptop\", \"price\": $1200.00, \"available\": True } Invalidity: The price value $1200.00 is not a valid JSON number (currency symbols are not allowed). The available value True is not a valid JSON boolean (must be lowercase true or false). ----------------- 4. Mismatched Braces or Brackets: Code { \"user\": { \"id\": 123, \"name\": \"Bob\", \"details\": [ \"email\": \"bob@example.com\" } ] } Invalidity: The details array contains an object that is closed with a } instead of a ], and the array itself is closed with a ] after the object, leading to a structural mismatch. ----------------- 5. Unescaped Characters within Strings: Code { \"message\": \"He said, \"Hello!\"\" } Invalidity: The double quotes within the string \"Hello!\" are not escaped, causing a syntax error. They should be \\\"Hello!\\\". ----------------- 6. Comments within JSON: Code { // This is a comment \"data\": \"some value\" } Invalidity: JSON does not support comments. ----------------- 7. Missing Colons or Values in Key-Value Pairs: Code { \"key1\": \"value1\", \"key2\" \"key3\": \"value3\" } Invalidity: The key2 entry is missing a colon and a value. ----------------- 8. Invalid JSON Structure (e.g., array with object syntax): Code [ \"item1\": \"value1\", \"item2\": \"value2\" ] Invalidity: An array cannot contain key-value pairs; it should contain elements directly. { \"key1\" : \"value1\", \"key2\" \"lk\" } ----------------- { \"key1\" : \"value1\" \"key2\" \"lk\" } ----------------- { \"key1\" : \"value1\", \"key2\" \"lk\" } ----------------- { \"key1\" : \"value1\", \"key2\" : mj } ----------------- { \"key1\" : \"value1\", \"key2\" : \"mj } ----------------- { \"key1\" : \"value1\", \"hhh\" : [ { \"key0\" : [{\"MMM\" : \"a\"}, \"b\",\"c\"], \"key2\" : \"mj\", \"key3\" : [ ----------------- [ \"mn\" {\"MMM\" : a\"} , \"b\" , \"c\" ] "; let substitution = "$1 ERROR_here>> "; // result will be a String with the substituted value let result = regex.replace_all(string, substitution); println!("{}", result); }

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/