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Regular Expressions Cookbook, 2nd Edition

Cover of Regular Expressions Cookbook, 2nd Edition by Jan Goyvaerts... Published by O'Reilly Media, Inc.
  1. Regular Expressions Cookbook
  2. Preface
    1. Caught in the Snarls of Different Versions
    2. Intended Audience
    3. Technology Covered
    4. Organization of This Book
    5. Conventions Used in This Book
    6. Using Code Examples
    7. Safari® Books Online
    8. How to Contact Us
    9. Acknowledgments
  3. 1. Introduction to Regular Expressions
    1. Regular Expressions Defined
      1. Many Flavors of Regular Expressions
      2. Regex Flavors Covered by This Book
    2. Search and Replace with Regular Expressions
      1. Many Flavors of Replacement Text
    3. Tools for Working with Regular Expressions
      1. RegexBuddy
      2. RegexPal
      3. RegexMagic
      4. More Online Regex Testers
      5. More Desktop Regular Expression Testers
      6. grep
      7. Popular Text Editors
  4. 2. Basic Regular Expression Skills
    1. 2.1. Match Literal Text
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    2. 2.2. Match Nonprintable Characters
      1. Problem
      2. Solution
      3. Discussion
      4. Variations on Representations of Nonprinting Characters
      5. See Also
    3. 2.3. Match One of Many Characters
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. Flavor-Specific Features
      6. See Also
    4. 2.4. Match Any Character
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    5. 2.5. Match Something at the Start and/or the End of a Line
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    6. 2.6. Match Whole Words
      1. Problem
      2. Solution
      3. Discussion
      4. Word Characters
      5. See Also
    7. 2.7. Unicode Code Points, Categories, Blocks, and Scripts
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    8. 2.8. Match One of Several Alternatives
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 2.9. Group and Capture Parts of the Match
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    10. 2.10. Match Previously Matched Text Again
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    11. 2.11. Capture and Name Parts of the Match
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 2.12. Repeat Part of the Regex a Certain Number of Times
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    13. 2.13. Choose Minimal or Maximal Repetition
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 2.14. Eliminate Needless Backtracking
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    15. 2.15. Prevent Runaway Repetition
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    16. 2.16. Test for a Match Without Adding It to the Overall Match
      1. Problem
      2. Solution
      3. Discussion
      4. Alternative to Lookbehind
      5. Solution Without Lookbehind
      6. See Also
    17. 2.17. Match One of Two Alternatives Based on a Condition
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    18. 2.18. Add Comments to a Regular Expression
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
    19. 2.19. Insert Literal Text into the Replacement Text
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    20. 2.20. Insert the Regex Match into the Replacement Text
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    21. 2.21. Insert Part of the Regex Match into the Replacement Text
      1. Problem
      2. Solution
      3. Discussion
      4. Solution Using Named Capture
      5. See Also
    22. 2.22. Insert Match Context into the Replacement Text
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  5. 3. Programming with Regular Expressions
    1. Programming Languages and Regex Flavors
      1. Languages Covered in This Chapter
      2. More Programming Languages
    2. 3.1. Literal Regular Expressions in Source Code
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 3.2. Import the Regular Expression Library
      1. Problem
      2. Solution
      3. Discussion
    4. 3.3. Create Regular Expression Objects
      1. Problem
      2. Solution
      3. Discussion
      4. Compiling a Regular Expression Down to CIL
      5. Discussion
      6. See Also
    5. 3.4. Set Regular Expression Options
      1. Problem
      2. Solution
      3. Discussion
      4. Additional Language-Specific Options
      5. See Also
    6. 3.5. Test If a Match Can Be Found Within a Subject String
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 3.6. Test Whether a Regex Matches the Subject String Entirely
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 3.7. Retrieve the Matched Text
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 3.8. Determine the Position and Length of the Match
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 3.9. Retrieve Part of the Matched Text
      1. Problem
      2. Solution
      3. Discussion
      4. Named Capture
      5. See Also
    11. 3.10. Retrieve a List of All Matches
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 3.11. Iterate over All Matches
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    13. 3.12. Validate Matches in Procedural Code
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 3.13. Find a Match Within Another Match
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    15. 3.14. Replace All Matches
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    16. 3.15. Replace Matches Reusing Parts of the Match
      1. Problem
      2. Solution
      3. Discussion
      4. Named Capture
      5. See Also
    17. 3.16. Replace Matches with Replacements Generated in Code
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    18. 3.17. Replace All Matches Within the Matches of Another Regex
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    19. 3.18. Replace All Matches Between the Matches of Another Regex
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    20. 3.19. Split a String
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    21. 3.20. Split a String, Keeping the Regex Matches
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    22. 3.21. Search Line by Line
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    23. Construct a Parser
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  6. 4. Validation and Formatting
    1. 4.1. Validate Email Addresses
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    2. 4.2. Validate and Format North American Phone Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    3. 4.3. Validate International Phone Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    4. 4.4. Validate Traditional Date Formats
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    5. 4.5. Validate Traditional Date Formats, Excluding Invalid Dates
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    6. 4.6. Validate Traditional Time Formats
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    7. 4.7. Validate ISO 8601 Dates and Times
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 4.8. Limit Input to Alphanumeric Characters
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    9. 4.9. Limit the Length of Text
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    10. 4.10. Limit the Number of Lines in Text
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    11. 4.11. Validate Affirmative Responses
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 4.12. Validate Social Security Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    13. 4.13. Validate ISBNs
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    14. 4.14. Validate ZIP Codes
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    15. 4.15. Validate Canadian Postal Codes
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    16. 4.16. Validate U.K. Postcodes
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    17. 4.17. Find Addresses with Post Office Boxes
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    18. 4.18. Reformat Names From “FirstName LastName” to “LastName, FirstName”
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    19. 4.19. Validate Password Complexity
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    20. 4.20. Validate Credit Card Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. Extra Validation with the Luhn Algorithm
      5. See Also
    21. 4.21. European VAT Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
  7. 5. Words, Lines, and Special Characters
    1. 5.1. Find a Specific Word
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    2. 5.2. Find Any of Multiple Words
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 5.3. Find Similar Words
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 5.4. Find All Except a Specific Word
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    5. 5.5. Find Any Word Not Followed by a Specific Word
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    6. 5.6. Find Any Word Not Preceded by a Specific Word
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    7. 5.7. Find Words Near Each Other
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    8. 5.8. Find Repeated Words
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    9. 5.9. Remove Duplicate Lines
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 5.10. Match Complete Lines That Contain a Word
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    11. 5.11. Match Complete Lines That Do Not Contain a Word
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 5.12. Trim Leading and Trailing Whitespace
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    13. 5.13. Replace Repeated Whitespace with a Single Space
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 5.14. Escape Regular Expression Metacharacters
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
  8. 6. Numbers
    1. 6.1. Integer Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    2. 6.2. Hexadecimal Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 6.3. Binary Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 6.4. Octal Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 6.5. Decimal Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 6.6. Strip Leading Zeros
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 6.7. Numbers Within a Certain Range
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 6.8. Hexadecimal Numbers Within a Certain Range
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 6.9. Integer Numbers with Separators
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 6.10. Floating-Point Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    11. 6.11. Numbers with Thousand Separators
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 6.12. Add Thousand Separators to Numbers
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    13. 6.13. Roman Numerals
      1. Problem
      2. Solution
      3. Discussion
      4. Convert Roman Numerals to Decimal
      5. See Also
  9. 7. Source Code and Log Files
    1. Keywords
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    2. Identifiers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. Numeric Constants
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. Operators
      1. Problem
      2. Solution
      3. Discussion
    5. Single-Line Comments
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. Multiline Comments
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    7. All Comments
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. Strings
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    9. Strings with Escapes
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    10. Regex Literals
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    11. Here Documents
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. Common Log Format
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    13. Combined Log Format
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. Broken Links Reported in Web Logs
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  10. 8. URLs, Paths, and Internet Addresses
    1. 8.1. Validating URLs
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    2. 8.2. Finding URLs Within Full Text
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 8.3. Finding Quoted URLs in Full Text
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 8.4. Finding URLs with Parentheses in Full Text
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 8.5. Turn URLs into Links
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 8.6. Validating URNs
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 8.7. Validating Generic URLs
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 8.8. Extracting the Scheme from a URL
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 8.9. Extracting the User from a URL
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 8.10. Extracting the Host from a URL
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    11. 8.11. Extracting the Port from a URL
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 8.12. Extracting the Path from a URL
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    13. 8.13. Extracting the Query from a URL
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 8.14. Extracting the Fragment from a URL
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    15. 8.15. Validating Domain Names
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    16. 8.16. Matching IPv4 Addresses
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    17. 8.17. Matching IPv6 Addresses
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    18. 8.18. Validate Windows Paths
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    19. 8.19. Split Windows Paths into Their Parts
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    20. 8.20. Extract the Drive Letter from a Windows Path
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    21. 8.21. Extract the Server and Share from a UNC Path
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    22. 8.22. Extract the Folder from a Windows Path
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    23. 8.23. Extract the Filename from a Windows Path
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    24. 8.24. Extract the File Extension from a Windows Path
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    25. 8.25. Strip Invalid Characters from Filenames
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  11. 9. Markup and Data Formats
    1. Processing Markup and Data Formats with Regular Expressions
      1. Basic Rules for Formats Covered in This Chapter
    2. 9.1. Find XML-Style Tags
      1. Problem
      2. Solution
      3. Discussion
      4. Skip Tricky (X)HTML and XML Sections
      5. See Also
    3. 9.2. Replace <b> Tags with <strong>
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    4. 9.3. Remove All XML-Style Tags Except <em> and <strong>
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    5. 9.4. Match XML Names
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    6. 9.5. Convert Plain Text to HTML by Adding <p> and <br> Tags
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 9.6. Decode XML Entities
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 9.7. Find a Specific Attribute in XML-Style Tags
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 9.8. Add a cellspacing Attribute to <table> Tags That Do Not Already Include It
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 9.9. Remove XML-Style Comments
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    11. 9.10. Find Words Within XML-Style Comments
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    12. 9.11. Change the Delimiter Used in CSV Files
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    13. 9.12. Extract CSV Fields from a Specific Column
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    14. 9.13. Match INI Section Headers
      1. Problem
      2. Solution
      3. Discussion
      4. Variations
      5. See Also
    15. 9.14. Match INI Section Blocks
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    16. 9.15. Match INI Name-Value Pairs
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  12. Index
  13. About the Authors
  14. Colophon
  15. Copyright
O'Reilly logo

4.7. Validate ISO 8601 Dates and Times

Problem

You want to match dates and/or times in the official ISO 8601 format, which is the basis for many standardized date and time formats. For example, in XML Schema, the built-in date, time, and dateTime types are all based on ISO 8601.

Solution

The ISO 8601 standard defines a wide range of date and time formats. Most applications that use ISO 8601 only use a subset of it. These solutions match the most commonly used ISO 8601 date and time formats. We’ve also added solutions for XML Schema, which is one particular implementation of ISO 8601.

Dates

The following matches a calendar month (e.g., 2008-08). The hyphen is required:

^([0-9]{4})-(1[0-2]|0[1-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Named capture makes the regular expression and any code that may reference the capturing groups easier to read:

^(?<year>[0-9]{4})-(?<month>1[0-2]|0[1-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Python uses a different syntax for named capture, adding a P. For brevity, we only show one solution using the Python syntax. All the other solutions using .NET-style named capture can be easily adapted to Python-style named capture in the same way.

^(?P<year>[0-9]{4})-(?P<month>1[0-2]|0[1-9])$
Regex options: None
Regex flavors: PCRE, Python

ISO 8601 allows hyphens to be omitted from calendar dates, making both 2010-08-20 and 20100820 valid representations of the same date. The following regex accounts for this, but also allows for invalid formats like YYYY-MMDD and YYYYMM-DD.

^([0-9]{4})-?(1[0-2]|0[1-9])-?(3[01]|0[1-9]|[12][0-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>[0-9]{4})-?(?<month>1[0-2]|0[1-9])-?↵
(?<day>3[01]|0[1-9]|[12][0-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Calendar date, such as 2008-08-30 or 20080830. The hyphens are optional. This regex uses a capturing group and a backreference to match YYYY-MM-DD or YYYYMMDD, but not YYYY-MMDD or YYYYMM-DD.

^([0-9]{4})(-?)(1[0-2]|0[1-9])\2(3[01]|0[1-9]|[12][0-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>[0-9]{4})(?<hyphen>-?)(?<month>1[0-2]|0[1-9])↵
\k<hyphen>(?<day>3[01]|0[1-9]|[12][0-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Python also uses a different syntax for named backreferences:

^(?P<year>[0-9]{4})(?P<hyphen>-?)(?P<month>1[0-2]|0[1-9])↵
(?P=hyphen)(?<day>3[01]|0[1-9]|[12][0-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Ordinal date (e.g., 2008-243). The hyphen is optional:

^([0-9]{4})-?(36[0-6]|3[0-5][0-9]|[12][0-9]{2}|0[1-9][0-9]|00[1-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>[0-9]{4})-?↵
(?<day>36[0-6]|3[0-5][0-9]|[12][0-9]{2}|0[1-9][0-9]|00[1-9])$
Regex options: None
Regex flavors: .NET, Java 7, PCRE 7, Perl 5.10, Ruby 1.9

Weeks

Week of the year (e.g., 2008-W35). The hyphen is optional:

^([0-9]{4})-?W(5[0-3]|[1-4][0-9]|0[1-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>[0-9]{4})-?W(?<week>5[0-3]|[1-4][0-9]|0[1-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Week date (e.g., 2008-W35-6). The hyphens are optional.

^([0-9]{4})-?W(5[0-3]|[1-4][0-9]|0[1-9])-?([1-7])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>[0-9]{4})-?W(?<week>5[0-3]|[1-4][0-9]|0[1-9])-?(?<day>[1-7])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Times

Hours and minutes (e.g., 17:21). The colon is optional:

^(2[0-3]|[01][0-9]):?([0-5][0-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<hour>2[0-3]|[01][0-9]):?(?<minute>[0-5][0-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Hours, minutes, and seconds (e.g., 17:21:59). The colons are optional:

^(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<hour>2[0-3]|[01][0-9]):?(?<minute>[0-5][0-9]):?↵
(?<second>[0-5][0-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Time zone designator (e.g., Z, +07 or +07:00). The colons and the minutes are optional:

^(Z|[+-](?:2[0-3]|[01][0-9])(?::?(?:[0-5][0-9]))?)$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Hours, minutes, and seconds with time zone designator (e.g., 17:21:59+07:00). All the colons are optional. The minutes in the time zone designator are also optional:

^(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])↵
(Z|[+-](?:2[0-3]|[01][0-9])(?::?(?:[0-5][0-9]))?)$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<hour>2[0-3]|[01][0-9]):?(?<minute>[0-5][0-9]):?(?<second>[0-5][0-9])↵
(?<timezone>Z|[+-](?:2[0-3]|[01][0-9])(?::?(?:[0-5][0-9]))?)$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Date and time

Calendar date with hours, minutes, and seconds (e.g., 2008-08-30 17:21:59 or 20080830 172159). A space is required between the date and the time. The hyphens and colons are optional. This regex matches dates and times that specify some hyphens or colons but omit others. This does not follow ISO 8601.

^([0-9]{4})-?(1[0-2]|0[1-9])-?(3[01]|0[1-9]|[12][0-9])↵
(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>[0-9]{4})-?(?<month>1[0-2]|0[1-9])-?↵
(?<day>3[01]|0[1-9]|[12][0-9])(?<hour>2[0-3]|[01][0-9])↵
:?(?<minute>[0-5][0-9]):?(?<second>[0-5][0-9])$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

A more complicated solution is needed if we want to match date and time values that specify either all of the hyphens and colons, or none of them. The cleanest solution is to use conditionals. But only some flavors support conditionals.

^([0-9]{4})(-)?(1[0-2]|0[1-9])(?(2)-)(3[01]|0[1-9]|[12][0-9])↵
(2[0-3]|[01][0-9])(?(2):)([0-5][0-9])(?(2):)([0-5][0-9])$
Regex options: None
Regex flavors: .NET, PCRE, Perl, Python
^(?<year>[0-9]{4})(?<hyphen>-)?(?<month>1[0-2]|0[1-9])↵
(?(hyphen)-)(?<day>3[01]|0[1-9]|[12][0-9])(?<hour>2[0-3]|[01][0-9])↵
(?(hyphen):)(?<minute>[0-5][0-9])(?(hyphen):)(?<second>[0-5][0-9])$
Regex options: None
Regex flavors: .NET, PCRE 7, Perl 5.10
^(?P<year>[0-9]{4})(?P<hyphen>-)?(?P<month>1[0-2]|0[1-9])↵
(?(hyphen)-)(?P<day>3[01]|0[1-9]|[12][0-9])(?P<hour>2[0-3]|[01][0-9])↵
(?(hyphen):)(?P<minute>[0-5][0-9])(?(hyphen):)(?P<second>[0-5][0-9])$
Regex options: None
Regex flavors: PCRE, Perl 5.10, Python

If conditionals are not available, then we have to use alternation to spell out the alternatives with and without delimiters.

^(?:([0-9]{4})-?(1[0-2]|0[1-9])-?(3[01]|0[1-9]|[12][0-9])↵
(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])|↵
([0-9]{4})(1[0-2]|0[1-9])(3[01]|0[1-9]|[12][0-9])↵
(2[0-3]|[01][0-9])([0-5][0-9])([0-5][0-9]))$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

XML Schema dates and times

The date and time types defined in the XML Schema standard are based on the ISO 8601 standard. The date types allow negative years for years before the start of the calendar (B.C. years). It also allows for years with more than four digits, but not for years with fewer than four digits. Years with more than four digits must not have leading zeros. If you only want to allow years with four digits as in the preceding solutions, remove -?(?:[1-9][0-9]*)? from the following solutions.

Date, with optional time zone (e.g., 2008-08-30 or 2008-08-30+07:00). Hyphens are required. This is the XML Schema date type:

^(-?(?:[1-9][0-9]*)?[0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])↵
(Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>-?(?:[1-9][0-9]*)?[0-9]{4})-(?<month>1[0-2]|0[1-9])-↵
(?<day>3[01]|0[1-9]|[12][0-9])↵
(?<timezone>Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Time, with optional fractional seconds and time zone (e.g., 01:45:36 or 01:45:36.123+07:00). There is no limit on the number of digits for the fractional seconds. This is the XML Schema time type:

^(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])(\.[0-9]+)?↵
(Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<hour>2[0-3]|[01][0-9]):(?<minute>[0-5][0-9]):(?<second>[0-5][0-9])↵
(?<frac>\.[0-9]+)?(?<timezone>Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Date and time, with optional fractional seconds and time zone (e.g., 2008-08-30T01:45:36 or 2008-08-30T01:45:36.123Z). This is the XML Schema dateTime type:

^(-?(?:[1-9][0-9]*)?[0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])↵
T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])(\.[0-9]+)?↵
(Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby
^(?<year>-?(?:[1-9][0-9]*)?[0-9]{4})-(?<month>1[0-2]|0[1-9])-↵
(?<day>3[01]|0[1-9]|[12][0-9])T(?<hour>2[0-3]|[01][0-9]):↵
(?<minute>[0-5][0-9]):(?<second>[0-5][0-9])(?<ms>\.[0-9]+)?↵
(?<timezone>Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
Regex options: None
Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9

Discussion

ISO 8601 defines a wide range of date and time formats. The regular expressions presented here cover the most common formats, but most systems that use ISO 8601 only use a subset. For example, in XML Schema dates and times, the hyphens and colons are mandatory. To make hyphens and colons mandatory, simply remove the question marks after them. To disallow hyphens and colons, remove the hyphens and colons along with the question mark that follows them. Do watch out for the noncapturing groups, which use the (?:) syntax. If a question mark and a colon follow an opening parenthesis, those three characters open a noncapturing group.

We put parentheses around all the number parts of the regexes. That makes it easy to retrieve the numbers for the years, months, days, hours, minutes, seconds, and time zones. Recipe 2.9 explains how parentheses create capturing groups. Recipe 3.9 explains how you can retrieve the text matched by those capturing groups in procedural code.

For most regexes, we also show an alternative using named capture. Some of these date and time formats may be unfamiliar to you or your fellow developers. Named capture makes the regex easier to understand. .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, and Ruby 1.9 support the (?<name>) syntax used in the solutions in this recipe. All versions of PCRE and Python covered in this book support the alternative (?P<name>) syntax, which adds a P. See Recipes 2.11 and 3.9 for details.

The number ranges in all the regexes are strict. For example, the calendar day is restricted between 01 and 31. You’ll never end up with day 32 or month 13. None of the regexes here attempts to exclude invalid day and month combinations, such as February 31st; Recipe 4.5 explains how you can deal with that.

The regular expressions, except those in the XML Schema subsection, make the individual hyphens and colons optional. This does not follow ISO 8601 exactly. For example, 1733:26 is not a valid ISO 8601 time, but will be accepted by the time regexes. Requiring all hyphens and colons to be present or omitted at the same time makes your regex quite a bit more complex.

If the delimiters are all the same, we can do this quite easily using a capturing group for the first delimiter and backreferences for the remaining delimiters. The “dates” subsection of the “Solution” section shows an example. For the first hyphen, we use (-?), (?<hyphen>-?) or (?P<hyphen>-?) to match an optional hyphen and capture it into a named or numbered group. If the hyphen was omitted, the capturing group stores the zero-length string. The question mark that makes the hyphen optional must be inside the group. If we made the group itself optional, then backreferences to that group would always fail to match if the hyphen was not matched, as the group would not have participated in the match at all. For the remaining hyphens, we use \2, \k<hyphen>, or (?P=hyphen) to match the same text that was matched by the capturing group, which is either a hyphen or nothing at all, depending on whether the first hyphen was matched or not. When using numbered capture, make sure to use the correct number for the backreference.

If the delimiters are different, such as when matching a single string with both a date and a time, the solution is more complex. The “date and time” subsection shows an example. This time, we use (-)?, (?<hyphen>-)? or (?P<hyphen>-)? to match the hyphen. Now the question mark is outside the capturing group so that it will not participate in the match at all when the hyphen is omitted. This allows us to use the capturing group with a conditional. (?(2)-) matches a hyphen and (?(2):) matches a colon if the second capturing group participated in the match. The conditionals have no alternative, which means they will match nothing at all (but still succeed) when the second capturing group did not participate in the match. (?(hyphen)-) and (?(hyphen):) do the same using named capture.

Only some flavors support conditionals. If conditionals are not available, the only solution is to use alternation to spell out the two alternatives with and without delimiters. The disadvantage of this solution is that it results in two capturing groups for each part of the date and time. Only one of the two sets of capturing groups will participate in the match. Code that uses this regex will have to check both groups.

See Also

This chapter has several other recipes for matching dates and times. Recipes 4.4 and 4.5 show how to validate traditional date formats. Recipe 4.6 shows how to validate traditional time formats.

Techniques used in the regular expressions in this recipe are discussed in Chapter 2. Recipe 2.3 explains character classes. Recipe 2.5 explains anchors. Recipe 2.8 explains alternation. Recipe 2.9 explains grouping. Recipe 2.10 explains backreferences. Recipe 2.11 explains named capturing groups. Recipe 2.12 explains repetition. Recipe 2.17 explains conditionals.

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