2.12. Repeat Part of the Regex a Certain Number of Times
Problem
Create regular expressions that match the following kinds of numbers:
A googol (a decimal number with 100 digits).
A 32-bit hexadecimal number.
A 32-bit hexadecimal number with an optional
h
suffix.A floating-point number with an optional integer part, a mandatory fractional part, and an optional exponent. Each part allows any number of digits.
Solution
Googol
\b\d{100}\b
Regex options: None |
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Hexadecimal number
\b[a-f0-9]{1,8}\b
Regex options: Case insensitive |
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Hexadecimal number with optional suffix
\b[a-f0-9]{1,8}h?\b
Regex options: Case insensitive |
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Floating-point number
\d*\.\d+(e\d+)?
Regex options: Case insensitive |
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Discussion
Fixed repetition
The quantifier ‹{
›,
where n
}n
is a nonnegative integer, repeats
the preceding regex token n
number of
times. The ‹\d{100}
› in
‹\b\d{100}\b
› matches a
string of 100 digits. You could achieve the same by typing ‹\d
› 100 times.
‹{1}
› repeats the
preceding token once, as it would without any quantifier. ‹ab{1}c
› is the same regex as
‹abc
›.
‹{0}
› repeats the
preceding token zero times, essentially deleting it from the regular
expression. ‹ab{0}c
› is
the same regex as ‹ac
›.
Variable repetition
For variable repetition, we use
the quantifier ‹{
›, where ...n,m
}
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