Parsing PHP regular expression metacharacters_PHP tutorial

What are the metacharacters of PHP regular expressions? What should we pay attention to when using PHP regular expression metacharacters? So here I will give you a detailed introduction to the types of PHP regular expression metacharacters and how to use them, etc.

Types of PHP regular expression metacharacters:

◆braces

◆plus sign

◆asterisk

◆Question mark

Specific use of PHP regular expression metacharacters:

PHP regular expression metacharacters have a special category in PHP regular expressions Meaningful characters used to describe the way in which their leading characters (that is, the characters before metacharacters) appear in the matched object. Metacharacters themselves are single characters, but different or identical metacharacters can be combined to form large metacharacters.

◆Braces: Braces are used to accurately specify the number of occurrences of matching metacharacters

For example, "/pre{1,5}/" means that the matching object can be "pre", " pree" and "preeeee", a string of 1 to 5 "e" appears after "pr". Or "/pre{,5}/" means pre appears between 0 and 5 times.

◆Plus sign: The "+" character is used to match the character before the metacharacter appearing one or more times

For example, "/ac+/" means that the matched object can be "act", "account", "acccc" and other strings with one or more "c" appearing after "a". "+" is equivalent to "{1,}".

◆Asterisk: The "*" character is used to match the character before the metacharacter appearing zero or more times

For example, "/ac*/" means that the matched object can be "app ", "acp", "accp" and other strings in which zero or more "c" appear after "a". "*" is equivalent to "{0,}".

◆Question mark: "?" character is used to match zero or one occurrence of the character before the metacharacter

For example, "/ac?/" means that the matching object can be "a", "acp", "acwp" such that zero or one "c" string appears after "a". "?" also plays a very important role in regular expressions, that is, "greedy mode".

This is the brief introduction to PHP regular expression metacharacters. I hope it will be helpful for you to understand and master PHP regular expression metacharacters.

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