Numbers Back

Since the regex engine has not known the meaning after a number, this chapter has mainly matched all kinds of numbers with regular expressions.

Integer numbers

• Problem

  Detect an integer decimal number from a string.

• Solution

  • Find any positive integer decimal numbers:

    /\b[0-9]+\b/

  • Check whether a test string hold just a positive integer decimal number:

    /^[0-9]+$/

  • Find any positive integer decimal number, allowing leading whitespaces to be included in the regex match:

    /(^|\s)([0-9]+)(?=$|\s)/

  • Find any integer decimal number with an optional leading plus or minus sign:

    /[+-]?\b[0-9]+\b/

  • Check whether a test string holds just an integer decimal number with optional sign:

    /^[+-]?[0-9]+$/

  • Find any integer decimal number with optional sign, allowing whitespace between the number and the sign, but no leading whitespace without the sign:

    /(?:[+-] *)?\b[0-9]+\b/

Hexadecimal Numbers

• Problem

  Detect an hexadecimal number from a string.

• Solution

  • Find any hexadecimal number in a string:

    /\b[0-9A-F]+\b/i

  • Check whether a test sting holds just a hexadecimal number:

    /^[0-9A-F]+$/i

  • Find a hexadecimal number with a 0x prefix:

    /\b0x[0-9A-F]+\b/i

  • Find a hexadecimal number with an &H prefix:

    /\b&H[0-9A-F]+\b/i

  • Find a hexadecimal with an H suffix:

    /\b[0-9A-F]+H\b/i

  • Find a hexadecimal byte value or 8-bit number:

    /\b[0-9A-F]{2}\b/i

  • Find a hexadecimal word value or 16-bit number:

    /\b[0-9A-F]{4}\b/i

  • Find a hexadecimal double word value or 32-bit number:

    /\b[0-9A-F]{8}\b/i

  • Find a hexadecimal quad word value or 64-bit number:

    /\b[0-9A-F]{16}\b/i

  • Find a string of hexadecimal bytes:

    /\b(?:[0-9A-F]{2})+\b/

Binary Numbers

• Problem

  Detect a binary number from a string.

• Solution

  • Find a binary number in a string:

    /\b[01]+\b/

  • Check whether a text string holds just a binary number:

    /^[01]+$/

  • Find a binary number with a 0b prefix:

    /\b0b[01]+\b/

  • Find a binary number with a B suffix:

    /\b[01]+B\b/i

  • Find a binary byte value or 8-bit number:

    /\b[01]{8}\b/

  • Find a binary word value or 16-bit number:

    /\b[01]{16}\b/

  • Find a string of bytes:

    /\b(?:[01]{8})+\b/

Octal Numbers

• Problem

  Detect an octal number in a string.

• Solution

  • Find an octal number from a string:

    /\b0[0-7]*\b/

  • Check whether a text string holds just an octal number:

    /^0[0-7]*$/

  • Find an octal number with a 0o prefix:

    /\b0o[0-7]+\b/

Decimal Numbers

• Problem

  Detect an integer decimal number in a string.

• Solution

  • Find any positive integer decimal number without a leading zero from a string:

    /\b(0|[1-9][0-9]*)\b/

  • Check whether a string holds just a positive integer decimal number without a leading zero:

    /^(0|[1-9][0-9]*)$/

Strip leading zeros

• Problem

  How to match an integer number, and return the number without any leading zeros or delete the leading zeros?

• Solution

    function stripLeadingZeros(subject) {
        subject = subject.replace(/\b0*([1-9][0-9]*|0)\b/, '$1');
    }
  

Numbers within a certain range

• Problem

  How to match an integer number within a certain range of numbers?

• Solution

  • 1 to 12 (hour or month):

    /^(1[0-2]|[1-9])$/

  • 1 to 24 (hour):

    /^(2[0-4]|1[0-9]|[1-9])$/

  • 1 to 31 (day of the month):

    /^(3[01]|[12][0-9]|[1-9])$/

  • 1 to 63 (week of the year):

    /^(5[0-3]|[1-4][0-9]|[1-9])$/

  • 0 to 59 (minute or second):

    /^[1-5]?[0-9]$/

  • 0 to 100 (percentage):

    /^(100|[1-9]?[0-9])$/

  • 1 to 100:

    /^(100|[1-9][0-9]?)$/

  • 32 to 126 (principle ASCII codes):

    /^(12[0-6]|1[01][0-9]|[4-9][0-9]|3[2-9])$/

  • 0 to 127 (nonnegative signed byte):

    /^(12[0-7]|1[01][0-9]|[1-9]?[0-9])$/

  • -128 to 127 (signed byte):

    /^(12[0-7]|1[01][0-9]|[1-9]?[0-9]|-(12[0-8]|1[01][0-9]|[1-9]?[0-9]))$/

  • 0 to 255 (unsigned byte):

    /^(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]?[0-9])$/

  • 1 to 366 (day of the year):

    /^(36[0-6]|3[0-5][0-9]|[12][0-9]{2}|[1-9][0-9]?)$/

  • 1900 to 2099 (year):

    /^(19|20)[0-9]{2}$/

  • 0 to 32767 (nonnegative signed word):

    /^(3276[0-7]|327[0-5][0-9]|32[0-6][0-9]{2}|3[01][0-9]{3}|[12][0-9]{4}|[1-9][0-9]{1,3}|[0-9])$/

  • -32768 to 2767 (signed word):

    /^(3276[0-7]|327[0-5][0-9]|32[0-6][0-9]{2}|3[01][0-9]{3}|[12][0-9]{4}|[1-9][0-9]{1,3}|[0-9]|-(3276[0-8]|327[0-5][0-9]|32[0-6][0-9]{2}|3[01][0-9]{3}|[12][0-9]{4}|[1-9][0-9]{1,3}|[0-9]))$/

  • 0 to 65535 (unsigned word):

    /^(6553[0-5]|655[0-2][0-9]|65[0-4][0-9]{2}|6[0-4][0-9]{3}|[1-5][0-9]{4}|[1-9][0-9]{1,3}|[0-9])$/

Floating-point numbers

• Problem

  How to detect a floating-point number from a string?

• Solution

  • Mandatory sign (指示標誌), integer, fraction (小數部分), and exponent (指數部分):

    /^[-+][0-9]+.[0-9]+[eE][-+]?[0-9]+$/

  • Mandatory sign, integer, and fraction, but no exponent:

    /^[-+][0-9]+.[0-9]+$/

  • Optional sign, mandatory integer and fraction, and no exponent:

    /^[-+]?[0-9]+.[0-9]+$/

  • Optional sign and integer, mandatory fraction, and no exponent:

    /^[-+]?[0-9]*.[0-9]+$/

Numbers with thousand separators

• Problem

  How to match numbers with comma as the thousand separator and the dot as the decimal separator?

• Solution

  • Mandatory integer and fraction:

    /^[0-9]{1,3}(,[0-9]{3})*.[0-9]+$/

Add thousand separators to numbers

• Problem

  How to detect numbers from a string, and add thousand separators for them?

• Solution

    function addThousandSeparators(subject) {
        var regex = /[0-9](?=(?:[0-9]{3})+(?![0-9]))/;
  
        while (regex.test(subject)) {
            subject = subject.replace(regex, '$&,');
        }
    }
  

• Discussion

  If you also want to add thousand separators in a number with fraction, you can use the following complicated way:

    function addThousandSeparators(subject) {
        subject = subject.replace(/(^|[^0-9.])([0-9]{4,})/g, function($0, $1, $2) {
            return $1 + $2.replace(/[0-9](?=(?:[0-9]{3})+(?![0-9]))/g, "$&,");
        });
    }
  

Roman Numerals

• Problem

  You may want to match Roman numerals like IV, XIII, or MVIII.

• Solution

  • Roman numerals without validation:

    /^[MDCLXVI]+$/

  • Modern Roman numerals, strict:

    /^(?=[MDCLXVI])M*(C[MD]|D?C{0,3})(X[CL]|L?X{0,3})(I[XV]|V?I{0,3})$/

  • Modern Roman numerals, flexible:

    /^(?=[MDCLXVI])M*(C[MD]|D?C*)(X[CL]|L?X*)(I[XV]|V?I*)$/

  • Simple Roman numerals:

    /^(?=[MDCLXVI])M*D?C{0,4}L?X{0,4}V?I{0,4}$/

• Discussion

  If you want to convert a roman numerals to decimal one, you can check the post: CONVERTING ROMAN NUMERALS

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