Regular Expression Basics Tutorial (PHP)

Regular expressions

A regular expression is a string search tool and a matching tool

The regular expression functions commonly used in PHP are as follows:

Preg_match ($pattern, $subject) Form validation, etc.

Preg_match_all ($pattern, $subject,array& $matches)

Preg_replace ($pattern, $replacement, $subject) illegal word filtering, etc.

Preg_filter ($pattern, $replacement, $subject)

Preg_grep ($pattern, array, $input)

Preg_split ($pattern, $subject)

Preg_quote ($STR)

$pattern = Regular Expression

$subject = matching Target data

Regular expression basic Syntax delimiter

$pattern = '/[0-9]/';

#[0-9]#

{[0-9]}

Atomic

• Visible atoms

Characters that are visible to the naked eye with the keyboard output in a Unicode encoding table

What are they?

Punctuation: "_?. Wait a minute

--English alphanumeric A-Z, a-z,0-9

--Kanji, Japanese, Arabic and other language characters

--Physics Formula symbol

--Other visible characters

• Non-visible atoms

Line break \ n

Enter \ r

TAB \ t

Space

Other Invisible Symbols

Quantifiers

{n} indicates that the atom in front of it appears exactly n times

{N,} indicates that the atom in front of it appears at least n times

{N,m} indicates that the atom in front of it appears at least n times, with a minimum of M times

* Match 0, 1, or more of its previous atoms, i.e. {0,}

+ match 1 or more times before the atom, i.e. {1,}
? Matches 0 or 1 times its previous atom, which is {0,1}

Border control

^ matches where the string starts

$ matches the position of the end of the string

() match the whole of which is an atom

Mode unit

Correction mode: Default is greedy mode, lazy mode is actually added a capital of U such as/123456/u

Common correction modes

U: Lazy Match

U: Greedy match

I: Ignore the case of English letters

x: Ignore whitespace (enter, space, etc.)

S-let meta-character. Match all characters including line break

REGEXPL Regular Debugging Tools

In order to avoid the dislocation caused by different coding formats, it is recommended to convert the Chinese into Unicode encoding first.

Metacharacters

How to filter atoms

| Match two or more

[] matches any one of the atoms in the square brackets

[^] matches any character except for the atoms in square brackets

Metacharacters

The collection of atoms

Match any character except line break

. Any character other than a line break

\d matches any decimal number, i.e. [0-9]

\d matches any non-decimal number, i.e. [^0-9]

\s matches an invisible atom, i.e. [\f\n\r\t\v]

\s matches a visible atom, i.e. [^\f\n\r\t\v]

\w matches any number, letter, or underscore, i.e. [0-9a-za-z]

W: matches any word character that includes an underscore. Similar but not equivalent to "[a-za-z0-9_]", where the "word" character uses the Unicode character set.

\w: Matches any non-word character. Equivalent to "[^a-za-z0-9_]".

If you use Re.sub (R ' [_|\w] ', ', text) to remove all non-words or underscores "_",

If you use Re.sub (R ' [_|\w] ', ' x ', text), all ' _ ' and word characters will be replaced with ' X '

Common Regular Expressions

. + Non-null

1 (3|4|5|7|8) \d{9} matches the mobile number in mainland China

^\w+ (\.\w+) *@\w+ (\.\w+) +$ Verify the mailbox

^ (https?:/ /)? (\w+\.) +[a-za-z]+$ URL.

Development of Cottage Smarty template engine

How the template engine works

Get template source Files

Compile template (regular replacement)

Output to User

Imitation smarty simple template engine, in a standard PHP system, the template engine must be, for front-end engineers and back-end engineers to separate the work, and front-end engineers do not need to understand the backend code.

Online Debugging Tools

http://cs.smu.ca/~porter/csc/355/regexpal/

?: used when you don't want to be captured can improve program execution speed

Regular Expression Basics Tutorial (PHP)