6.5. Decimal 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. The number must not have a leading zero, as only octal numbers can have leading zeros. But the number zero itself is a valid decimal number.
Solution
Find any positive integer decimal number without a leading zero in a larger body of text:
\b(0|[1-9][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 without a leading zero:
\A(0|[1-9][0-9]*)\Z
Regex options: None |
Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby |
^(0|[1-9][0-9]*)$
Regex options: None |
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python |
Discussion
Recipe 6.1 shows a lot of solutions for
matching integer decimal numbers, along with a detailed explanation. But
the solutions in that recipe do not take into account that in many
programming languages, numbers with a leading zero are octal numbers
rather than decimal numbers. They simply use ‹[0-9]+
› to match any sequence of decimal
digits.
The solutions in this recipe exclude numbers with a leading zero,
while still matching the number zero itself. Instead of matching any
sequence of decimal digits with ‹[0-9]+
›, these regular expressions use ‹0|[1-9][0-9]*
› to match either the digit zero, or a decimal number with at least one digit that does not begin with a zero. Since the alternation ...
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