Regular expression character cluster (1)

In INTERNET programs, regular expressions are usually used to verify user input. After a user submits a FORM, it is not enough to determine whether the entered phone number, address, EMAIL address, and credit card number are valid. What is a character cluster?

In INTERNET programs, regular expressions are usually used to verify user input. After a user submits a FORM, it is not enough to determine whether the entered phone number, address, EMAIL address, and credit card number are valid.

Therefore, we need to use a more free way to describe the mode we want. it is a character cluster. To create a character cluster that represents all vowel characters, put all the vowel characters in a square bracket:

[AaEeIiOoUu]

This mode matches any vowel character, but can only represent one character. The font size can be used to indicate the range of a character, for example:

[A-z] // match all lowercase letters

[A-Z] // match all uppercase letters

[A-zA-Z] // match all letters

[0-9] // match all numbers

[0-9 \. \-] // match all numbers, periods, and periods

[\ F \ r \ t \ n] // match all white characters

Similarly, these are only one character, which is very important. If you want to match a string consisting of a lowercase letter and a number, such as "z2", "t6", or "g7 ″, if it is not "ab2", "r2d3", or "b52", use this mode:

^ [A-z] [0-9] $

Although [a-z] represents the range of 26 letters, it can only match strings with lowercase letters with the first character.

^ Indicates the start of a string, but it has another meaning. When ^ is used in square brackets, it indicates "not" or "excluded", which is often used to remove a character. In the preceding example, the first character must not be a number:

^ [^ 0-9] [0-9] $

This mode matches "& 5", "g7", and "-2", but does not match "12" and "66. The following are examples of how to exclude specific characters:

[^ A-z] // All characters except lowercase letters

[^ \/\ ^] // All characters except (\) (/) (^)

[^ \ "\ '] // All characters except double quotation marks (") and single quotation marks (')

Special character "." (Point, period) is used to represent all characters except the "new line" in a regular expression. Therefore, the pattern "^. 5 $" matches any two-character string that ends with a number 5 and starts with another non-New Line character. Mode "." can match any string, except for empty strings and strings containing only one "new line.

　　 PHP regular expressions have some built-in general character clusters. the list is as follows:

Character cluster meaning

[[: Alpha:] any letter

[[: Digit:] any number

[[: Alnum:] any letter or number

[[: Space:] any white characters

[[: Upper:] any uppercase letter

[[: Lower:] any lowercase letter

[[: Punct:] any punctuation marks

[[: Xdigit:] Any hexadecimal number, equivalent to [0-9a-fA-F]

The above is the details of the regular expression character cluster (1). For more information, see other related articles in the first PHP community!