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the 1th chapter first knowledge Regular expression Regular Expression Definitions

• Regular expressions are a tool for searching and matching strings

application Examples of regular expressions

• Mobile input
• Windows File Search
• Linux List file commands
• Website User Registration

the 2nd Chapter analysis of the function of regular expression   Regular expression functions commonly used in PHP

• $pattern = Regular expression
• $subject = target function to match

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

Code:

$pattern = '/[0-9]/'; $subject = ' weur3ui76as83s0tk9 '; $m 1 = $m 2 = array (); $t 1 = preg_match ($pattern, $subject, $m 1); $t 2 = Preg_match_all ($pattern, $subject, $m 2); Show ($m 1); echo ' Show ($m 2); echo ' Show ($t 1. ' | | '. $t 2);

• preg_replace ($pattern, $replacement, $subject)
• Preg_filter ($pattern, $replacement, $subject)

Code:

$pattern = Array ('/[0123]/', '/[456]/', '/[789]/'); $subject = Array (' WEU ', ' r3ui ', ' 76as83 ', ' s ', ' 0tk9 '); $replacement = Array (' million ', ' thing ', ' house '); $str 1 = preg_replace ($pattern, $replacement, $subject);  $str 2 = Preg_filter ($pattern, $replacement, $subject); Show ($str 1); echo ' Show ($str 2);

• Preg_grep ($pattern, array $input)

Code:

$pattern = '/[0-9]/'; $subject = Array (' WEU ', ' r3ui ', ' 76as83 ', ' s ', ' 0tk9 '); $arr = Preg_grep ($pattern, array $input); Show ($arr);

• Preg_split ($pattern, $subject)

Code:

$pattern = '/[0-9]/'; $subject = ' Silver 2 sang 3, 3 ' da ~ '; $arr = preg_split ($pattern, $subject); Show ($arr);

• preg_quote ($str)

Code:

$str = ' qwer{asdf}[1234] '; $str = Preg_quote ($STR); Show ($STR);

PHP regular-expression functions Summary

• All start with Preg_.
• In addition to the Preg_quote function, the first parameter is a regular expression

• Preg_match-form inflammation, etc.
• Preg_match_all-illegal word filtering, etc.

3rd the basic syntax of regular expressions delimiting characters

• Represents the start and end of a regular expression
• /[0-9]/

Regular Expression Tools

• http://regexpal.com/

Atoms

• Visible atoms-characters that are visible to the naked eye with the keyboard output in a Unicode-encoded table

• What are they?

Punctuation " _ ? . ET-English alphanumeric A-Z, A-Z, 0-9-kanji, Japanese, Arabic and other languages-∑,∈,∮,≌, etc. physics formula symbols-other visible characters

• Invisible atoms-characters that are not visible to the naked eye after keyboard output in a Unicode encoding table

• What are they?

-line break \ n return \r-tab \t-Space-Other invisible symbols (Ps:unicode encoding conversion tool: Http://tool.oschina.net/encode)   Meta character

• How to filter atoms

- | Matches two or more branch selections-[] matches any atom in square brackets-[^] matches any character except for atoms in square brackets

• The collection of atoms

- . Match any character except newline-\d matches any decimal number, that is, [0-9]-\d matches any non-decimal number, that is, [^0-9]-\s matches an invisible atom, [\f\n\r\t\v]-\s matches a visible atom, i.e. [^\f\n\r\t\v] -\w matches any number, letter, or underscore, that is, [0-9a-za-z_]-\w matches any number, letter, or underscore, i.e. [^0-9a-za-z_] quantifier

• {n} indicates that the preceding atom appears exactly n times
• {N,} indicates that the preceding atom appears at least n times
• {N,m} indicates that the preceding atom appears at least n times, with a maximum 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}

boundary Control and pattern Unit

• ^ matches where the string starts
• $ matches the position of the end of the string
• () match the whole of which is a single atom

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