PHP Regular Expression review (2)--Basic syntax

1. Add "/....../" to both sides of the delimiter and use "#......#"

2. Atoms visible Atoms & smallest units of invisible atoms

Visible atoms: Characters that can be seen with the naked eye

Invisible atoms: atoms that are invisible to the naked eye, such as: \ n line break \ t tab

Suggestion: In about Chinese characters to match, first go to Webmaster tools, the Chinese characters into Unicode encoding, in the match, you can avoid coding different errors produced.

3. Meta-Characters

How to filter atoms

| Match two or more branch selections.

[.......] Matches any one of the atoms in the square brackets

[^.......] Match any character except the atoms in square brackets, note: [^ These two symbols must be joined together.

The collection of atoms

. Matches any character except the line break. equivalent to [^\n]

\d matches a decimal number [0-9]

\d matches a non-decimal number [^0-9]

\s matches an invisible atom [\t\n\r\f\v]

\s matches any one visible atom [^\t\n\r\f\v]

\w matches any number, letter, underscore [0-9a-za-z_]

\w matches any one non-digit, letter, underscore [^0-9a-za-z_]

4. quantifiers not only support atoms, they also support the collection of atoms.

{n} The atom in front of it just appears n times

{n,} The atoms in front of it appear at least n times

{n,m} The atom in front of it appears at least n times, with a maximum of M times

* Match 0 times, 1 times, multiple {0,}

+ match 1 times, multiple {1,}

？ Match 0 times, 1 times {0,1}

5. Border control

^ Must start with the next atom.

$ must end with the one atom before

() match the whole of which is an atom

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