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Regular Expressions Cookbook, 2nd Edition by Steven Levithan, Jan Goyvaerts

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6.10. Floating-Point Numbers

Problem

You want to match a floating-point number and specify whether the sign, integer, fraction and exponent parts of the number are required, optional, or disallowed. You don’t want to use the regular expression to restrict the numbers to a specific range, and instead leave that to procedural code, as explained in Recipe 3.12.

Solution

Mandatory sign, integer, fraction, and exponent:

^[-+][0-9]+\.[0-9]+[eE][-+]?[0-9]+$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

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

^[-+][0-9]+\.[0-9]+$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

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

^[-+]?[0-9]+\.[0-9]+$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

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

^[-+]?[0-9]*\.[0-9]+$
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Optional sign, integer, and fraction. If the integer part is omitted, the fraction is mandatory. If the fraction is omitted, the decimal dot must be omitted, too. No exponent.

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

Optional sign, integer, and fraction. If the integer part is omitted, the fraction is mandatory. If the fraction is omitted, the decimal dot is optional. No exponent.

^[-+]?([0-9]+(\.[0-9]*)?|\.[0-9]+)$ ...

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