Getting started with regular expressions: match the number of characters in a range

We will consider the matching of 000-999 again: "\ d {3}". Although it is correct, it can only match exactly 3 bits: 000, 001, 002... 100, 101... 999. Generally, we need to match numbers such as 0, 10, and 99. In this case, we need to specify numbers that can match one to three digits.

In a regular expression, the "{minimum, maximum}" syntax is used. It is used in the same way as the syntax described in the previous section that matches a fixed number of characters.

[0-9]{1,3}

Effect demonstration

100

001

1xxx

1001

1c

This example code

function reg_replace(){var test = document.getElementById("test");aim = "1[35][0-9]{9}";var regex = new RegExp("("+aim+")","g");test.innerHTML = test.innerHTML.replace(regex,"<span style='background-color:orange'>$1</span>");}

We found two problems: 1. We do not want "1234" to be matched. However, it is divided into two parts: "123" and "4" for matching, how can we prevent it from being matched? 2. Why is it divided into 123 and 4 instead of 1 and 234? We will leave it for further discussion.

Note two special cases:

• The minimum number can be 0, so "{0, 1}" is equivalent to "?".
• If you do not limit the maximum number, you can set it to null. Therefore, "\ d {1,}" is equivalent to "+", and "{0,}" is equivalent to "*".

"{" And "}" are also metacharacters. When we need to match them, use "\" for escape: "\ {" and "\}".

Additional reading

The topic list of this article is as follows:

1. What is a regular expression?
2. Getting started with regular expressions: match a Fixed Single Character
3. Getting started with regular expressions: matching any single character
4. Getting started with regular expressions: Use character groups
5. Getting started with regular expressions: Use character ranges in character groups
6. Getting started with regular expressions: Use of assense character groups
7. Getting started with regular expressions: matching null characters
8. Getting started with regular expressions: Match one or more characters
9. Regular Expression: matches zero or multiple characters.
10. Regular Expression entry: matches zero or one string.
11. Getting started with regular expressions: Match fixed numbers of Characters
12. Getting started with regular expressions: match the number of characters in a range
13. Getting started with regular expressions: greedy matching
14. Getting started with regular expressions: inert matching
15. Entry to Regular Expressions: two matching Modes
16. Getting started with regular expressions: match word boundaries
17. Getting started with regular expressions: boundary definition and relativity
18. Getting started with regular expressions: Match non-word boundaries
19. Getting started with regular expressions: match the beginning and end of a text
20. Entry to regular expression: submode
21. Regular Expression entry: "or" Match
22. Getting started with regular expressions: replacing with referenced text
23. Getting started with regular expressions: unmatched
24. Regular Expression Summary: Regular Expressions in JavaScript
25. Regular Expression Summary: advanced application of regular expressions in js