PHP Regular expression (Regular Expression) usage

Regular expression (Regular Expression)

Regular expression system:

1.POSIX

2.Perl

The regex used in PHP is pcre:

Note:pcre (Perl-compatible regular expressions, Perl compatible Regular Expressions)

Pcre Syntax:

1. Delimiters

must appear in pairs and can use any character other than 0-9a-za-z

2. Atomic

1. Both visible and invisible characters that need to be matched are atoms.

2. A regular expression contains at least one atom

3. When you need to match symbols such as "(", "[", "^" and so on that contain semantics, you need to escape with the backslash.

Atomic characters:

F Matching page breaks

N Match line break

R Matching Carriage return character

T-Match tab

V Matching Vertical Tabs

3. Meta character

Escape character

^ Match string at start

$ Match String End

. Matches any single character except "N"

* Match the preceding subexpression 0 or more times

+ Match previous subexpression 1 or more times

? Match the preceding subexpression 0 or 1 times

{n} matches n times

{n,} matches n times or more n times

{n,m} minimum match n times up to M times, (n<=m)

[] brackets represent atomic tables, and the atoms in the middle are equal in status. Matches any one of the characters in the table when it matches

[^] Caron, excluding the characters that are contained in the following atomic table.

(pattern) matches the pattern and gets the match.

Num matches a reference to the obtained Num.

(?:p Attern) match pattern but do not get this match

(? =pattern) positive forward check, non-fetch match, for example: Windows (? =xp|7) matches windows in Windows mismatch in Windows98

(?! =pattern) positive negation to check for non-fetch matches, for example: Windows (?! 98|2000), can match windows in XP, cannot match windows in Windows98

(? <=pattern) Reverse positive check, not get match. For example: (? <=my| postgre) SQL can match the SQL in MySQL and cannot match the SQL in MSSQL

(? <!pattern) reverse negation of the pre-search, not to obtain a match. For example: (? <! my| postgre) SQL matches the SQL in MSSQL and does not match the SQL in MySQL

B Match Word boundary

B matches a character other than a word boundary

　　　　

D matches any one number. equivalent to [0-9]

D matches any character other than a digit. equivalent to [^0-9]

s matches any white space character (including spaces, tabs, page breaks, and so on). equivalent to [FNRTV]

S matches any non-white-space character. equivalent to [^FNRTV]

　　　　

W matches any number, letter, or underline. equivalent to [0-9a-za-z]

W matches any character that is not numeric, alphanumeric, or underlined. equivalent to [^0-9a-za-z]

4. Pattern modifier

I do not case sensitive

M in this mode if there is a carriage return or line break, ^ and $ will match the beginning and end of each line

s let. can match n

x Ignore whitespace

U cancel Greed, equal to (. *?)

A is the same as ^ effect

D at the end without ignoring the carriage return, at the end of the $ character at the time, after the matching string plus carriage return, $ can still match it successfully. But plus d, the end of the carriage return, no longer match

Note: Regular expressions are matched from left to right

Regular expressions that are commonly used
1, nonnegative integer: "^d+$"

2, positive integer: "^[0-9]*[1-9][0-9]*$"

3, non-positive integer: "^ (-d+) | ( 0+)) $ "

4, Negative integer: "^-[0-9]*[1-9][0-9]*$"

5, Integer: "^-?d+$"

6, nonnegative floating-point number: "^d+ (. d+)? $"

7, positive floating-point number: "^ ((0-9) +.[ 0-9]*[1-9][0-9]*) | ([0-9]*[1-9][0-9]*. [0-9]+) | ([0-9]*[1-9][0-9]*)] $

8, non-positive floating-point number: "^ ((-d+.d+)?) | (0+ (. 0+)?)) $

9, negative floating point number: "^ (-((positive float)) $"

10. English string: "^[a-za-z]+$"

11, English capital string: "^[a-z]+$"

12, English lowercase string: "^[a-z]+$"

13, English character number string: "^[a-za-z0-9]+$"

14, the English numeral adds the underline string: "^w+$"

15, e-mail address: "^[w-]+ (. [ w-]+) *@[w-]+ (. [ w-]+) +$ "

16, URL: "^[a-za-z]+://(w+ (-w+) *) ( w+ (-w+) *)) * (? s*)? $ "

The following function, written in PHP, can get all the link addresses in any string $string ($string can be read directly from an HTML page file), and the result is returned in an array. The function automatically excludes e-mail addresses, And there are no duplicate elements in the returned array.

The code is as follows

Copy Code

function Getalllink ($string) { $string = Str_replace ("R", "", $string); $string = Str_replace ("n", "", $string); $regex [url] = "((http|https|ftp|telnet|news)://)? ([a-z0-9_-/.] +. [][a-z0-9:;&#@=_~%?/.,+-]+) "; $regex [email] = ([a-z0-9_-]+) @ ([a-z0-9_-]+.[ a-z0-9-._-]+) "; Remove the text between labels $string = Eregi_replace (">[^<>]+<", "><", $string); Remove JavaScript code $string = Eregi_replace ("<!--. *//-->", "", $string);

Remove HTML tags that are not <a>

code is as follows

copy code

$string = Eregi_replace ("<[^a][^<>]*>", "" ", $string); //Remove Email link $string = eregi_replace ("<a" ([]+) href= (["']*) mailto: ($regex [email]) ([" ']*] [^>]*> "," ", $ string); //Replace required page links $string = eregi_replace ("<a" ([]+) href= (["']*") ($regex [url]) ([']* ' [^>]*>], "\3t", $string ); $output [0] = Strtok ($string, "T"); while ($temp = Strtok ("T")) { if ($temp &&!in_array ($temp, $output) $output [+ + $i] = $temp; br>} Return $output; }

Here's a sample written in PHP syntax
Verify that the string contains only numbers and English, string length and between 4~16 characters

The code is as follows	Copy Code
<?php $str = ' a1234 '; if (Preg_match ("^[a-za-z0-9]{4,16}$", $str)) { echo "Validation succeeded";} else { echo "Validation lost?? quot;;}? >

Simple identification of the size of Taiwan's identity card

The code is as follows	Copy Code
<?php $str = ' a1234 '; if (Preg_match ("^ (?:d {15}|d{18}) $", $str)) { echo "Validation succeeded"; } else { echo "Validation lost?? quot;;} ?>

The following code implements a block of code in the text, like the code you see in the script house.

The code is as follows

Copy Code

function Codedisp ($code) { Global $discuzcodes; $discuzcodes [' Pcodecount ']++; $code = Htmlspecialchars (str_replace (' \ ", '" '), Preg_replace ("/^[nr]* (. +?) [nr]*$/is "," \1 ", $code))); $discuzcodes [' codehtml '] [$discuzcodes [' pcodecount ']] = "<br><div class=" Msgheader "><div class=" Right "><a href=" ### "class=" Smalltxt "onclick=" Copycode ($ (' phpcode$discuzcodes[codecount] '); >[Copy This Code]</a></div> code as follows: </div><div class= "Msgborder" id= "Phpcode$discuzcodes[codecount" > ". FHTML2 ($code)." </div><br> "; $discuzcodes [' Codecount ']++; return "[Tdiscuz_code_$discuzcodes[pcodecount]t]"; } $message = Preg_replace ("/s*[code]" (. +?) [/code]s*/ies "," Codedisp (' \1 ') ", $message); $message = Preg_replace ("/s*[html]" (. +?) [/html]s*/ies "," Htmldisp (' \1 ') ", $message);