PHP regular expression method to verify specific date format

In PHP development, we often need to verify or format dates. This article will introduce how to use PHP regular expressions to verify a specific date format.

1. Basic knowledge of regular expressions

Regular expressions are used to describe a method of matching a set of characters. They can flexibly search and replace text. In PHP, use the preg_match function for regular expression matching.

1.Basic syntax

Regular expressions are composed of various characters and metacharacters, among which metacharacters have special meanings and are used to control matching patterns.

For example, it means matching a or b or c, . means any character, ^ means the beginning of the line, and $ means the end of the line.

2. Quantifiers and boundaries

Quantifiers are used to match the number of times a character appears. For example, * means it appears 0 or more times, it means it appears at least once, ? means it appears 0 or 1 times. Second-rate.

Boundary characters are used to determine the matching position, ^ and $ represent the beginning and end of the line, and represent the beginning or end of the word.

3. Character set and escape

The character set is enclosed by [], which means matching any one of the characters. For example, [a-z] means matching any character from a to z.

Escape characters are used to escape special characters into ordinary characters, for example. means matching.

4. Grouping and backreference

The grouping is enclosed in (), which means it matches any group of characters and can be nested.

The back reference uses a number to indicate the previous group it refers to, for example, it refers to the first group.

2. Regular expression for verifying date format

The following are three different date formats and the corresponding regular expressions.

1. Year-month-day

The date format is YYYY-MM-DD, where the year is 4 digits, the month is 01-12, and the day number is 01-31.

Regular expression: /^[0-9]{4}-[0-9]{2}-[0-9]{2}$/.

where ^ represents the beginning of the line, $ represents the end of the line, [0-9] represents any number, {4} represents matching 4 times, and {2} represents matching 2 times.

2. Month/Day/Year

The date format is MM/DD/YYYY, where the year is 4 digits, the month is 01-12, and the day is 01-31.

Regular expression: /^[0-9]{2}/[0-9]{2}/[0-9]{4}$/.

Where / means matching the / character, and the rest are the same as above.

3.Day-Month-Year

The date format is DD-MM-YYYY, where the year is 4 digits, the month is 01-12, and the day is 01-31.

Regular expression: /^[0-9]{2}-[0-9]{2}-[0-9]{4}$/.

Among them - means matching - characters, and the rest are the same as above.

3. PHP code example

Using the preg_match function can easily verify the date format. The example is as follows:

<?php
$date = '2021-06-01';
$pattern = '/^[0-9]{4}-[0-9]{2}-[0-9]{2}$/';
if(preg_match($pattern, $date)){
    echo '日期格式正确';
} else {
    echo '日期格式错误';
}
?>

The output result is: the date format is correct.

<?php
$date = '06/01/2021';
$pattern = '/^[0-9]{2}/[0-9]{2}/[0-9]{4}$/';
if(preg_match($pattern, $date)){
    echo '日期格式正确';
} else {
    echo '日期格式错误';
}
?>

The output result is: the date format is correct.

<?php
$date = '01-06-2021';
$pattern = '/^[0-9]{2}-[0-9]{2}-[0-9]{4}$/';
if(preg_match($pattern, $date)){
    echo '日期格式正确';
} else {
    echo '日期格式错误';
}
?>

The output result is: the date format is correct.

4. Summary

This article introduces the method of using PHP regular expressions to verify a specific date format, including the basic syntax of regular expressions, quantifiers and boundaries, character sets and escapes , grouping and reverse references and other knowledge points. Finally, three common date formats and corresponding regular expressions are given, which can be selected according to actual needs.

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