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

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6.1. Integer Numbers

Problem

You want to find various kinds of integer decimal numbers in a larger body of text, or check whether a string variable holds an integer decimal number.

Solution

Find any positive integer decimal number in a larger body of text:

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

Check whether a text string holds just a positive integer decimal number:

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

Find any positive integer decimal number that stands alone in a larger body of text:

(?<=^|\s)[0-9]+(?=$|\s)
Regex options: None
Regex flavors: .NET, Java, PCRE, Ruby 1.9

For Perl and Python, we have to tweak the preceding solution, because they do not support alternatives of different lengths inside lookbehind:

(?:^|(?<=\s))[0-9]+(?=$|\s)
Regex options: None
Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby 1.9

Find any positive integer decimal number that stands alone in a larger body of text, allowing leading whitespace to be included in the regex match:

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

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

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

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

\A[+-]?[0-9]+\Z ...

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