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

r"
"

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

import Foundation let pattern = #"\A((?:(?!127\.0\.0\.1\s)[\s\S])*?)(?:\Z|127\.0\.0\.1\s+(?!localhost)\S+\n|(127\.0\.1\.1\s+\S+(?![\s\S]*\n127\.0\.0\.1\s)\n))"# let regex = try! NSRegularExpression(pattern: pattern) let testString = #""" 127.0.1.1 myhost 1.1.1.1 bla 127.0.0.1 bla 2.2.2.2 bla """# let stringRange = NSRange(location: 0, length: testString.utf16.count) let substitutionString = #"\1\2127.0.0.1 localhost\n"# let lookupRange = (testString as NSString).range(of: pattern, options: .regularExpression, range: stringRange) if lookupRange.intersection(stringRange) != nil { let result = regex.stringByReplacingMatches(in: testString, range: lookupRange, withTemplate: substitutionString) print(result) } else { print("No matches were found.") }

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 Swift 5.2, please visit: https://developer.apple.com/documentation/foundation/nsregularexpression