Repetition

Fixed repetition

The quantifier {n}, where n is an nonnegative integer, repeats the preceding regex token n times

\b\d{100}\b

• \d\d{0} is equivalent to \d
• \d\d{1} is equivalent to \d\d

Variable repetition

The quantifier {n,m}, where n is an nonnegative integer, and m is an nonnegative integer greater than n.

The following matches 1 to 8 digits:

\b\d{1,8}\b

• \d{10,10} is equivalent to \d

Infinite repetition

• \d{n,} matches n or more times of digits
• \d{1,} is equivalent to \d+
• \d{0,} is equivalent to \d*

Optional match

• \d{0,1} marks the digit can be omit in context
• \d{0,1} is equivalent to \d?
• matches empty string when the preceding token is absent

Repeating groups

• (?:abc){1,3} matches one to three occurrences of abc
• (?:abc)+ matches one or more occurrences of abc
• (?:abc)? matches any abc and empty strings