# 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 ...`

Get Regular Expressions Cookbook, 2nd Edition now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.