Strings and regular expressions in php, php regular expressions_PHP tutorial

Strings and regular expressions in php, php regular expressions

1. Characteristics of string types

1. PHP is a weakly typed language, and other data types can generally be directly applied to string function operations.

1:

//输出345

//输出345

//先查找hello常量，若没找到，将hello看做字符串使用

    2、字符串可以作为“数组”，是字符的集合。

1:

<span id="lnum3">   3:</span><span> <span>echo</span> $str[0];</span>

<span id="lnum5">   5:</span><span> <span>echo</span> $str[2];</span>

          但是字符串不是真的数组,不能使用数组的函数.如count($str)不会返回字符串长度。PHP引擎无法区分字符和数组，产生二义性。自PHP4起，已经用花括号替代方括号。

1:

<span id="lnum3">   3:</span><span> $str = <span>"www.ido321.com"</span>;</span>

<span id="lnum5">   5:</span><span> <span>echo</span> $str{1};</span>

<span id="lnum7">   7:</span><span> ?></span>

3. Double quote variable analysis

In PHP, when a string is defined with double quotes or delimiters, the variables in it will be parsed.

1:

"dwqs",<span>'add'</span> => <span>"www.ido321.com"</span>);

//可以解析，但是在方括号中不能使用引号

<span id="lnum5">   5:</span><span> <span>echo</span> <span>"{$arr['name']}"</span>;  <span>//可以解析,用花括号包含元素，name不带引号也是可以的</span></span>

<span id="lnum7">   7:</span><span> <span>//假设存在对象$square</span></span>

; <span>//可以解析</span>

; <span>//不可以解析，用花括号解决</span>

; <span>//可以解析</span>

2. String output function

3. Commonly used string format functions

PS: Most of PHP’s string processing functions do not modify the source string, but return a new string

4. Regular expressions

Regular expression describes a string matching pattern, through which strings are matched, searched, replaced and separated in specific functions. It consists of atoms, metacharacters and pattern modifiers. Three-part text pattern.

In PHP, there are two sets of regular processing function libraries: PCRE and POSIX. The former is named with preg_ prefix and is compatible with Perl; the latter is named with ereg_ prefix. The functions of the two are similar, but the efficiency of PCRE is slightly higher.

Regular expression processing function compatible with Perl language:

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1. Grammar

1.1 Delimiter: When using a pattern in a regular function compatible with Perl, you must add a delimiter to the pattern. Any character except letters, numbers and backslash () can be used as a delimiter

1:

<span id="lnum3">   3:</span><span> <span>echo</span> $m1 = <span>'/<\/\w+/'</span>;</span>

<span id="lnum5">   5:</span><span> <span>echo</span> $m3 = <span>'!^(?i)php[34]!'</span>;</span>

<span id="lnum7">   7:</span><span> ?></span>

1.2 Atoms: Atoms include normal characters, such as letters and numbers; non-printing characters, such as spaces and carriage returns; special characters and metacharacters , such as quotation marks, *, +, etc., must be escaped with ""; Customized atom table, such as [apj], [a-z]; Universal character type, Such as d, D.

1:

<span id="lnum3">   3:</span><span> $mail1 = <span>'/^[0-9a-zA-Z]+@[0-9a-zA-Z]+(\.[0-9a-zA-Z]+){0,3}$/'</span>;</span>

<span id="lnum5">   5:</span><span> ?></span>

1.3 Metacharacters: Characters with special meanings used to construct regular expressions. Perl can use various metacharacters to search for matches, such as *, +, ? .Common metacharacters are as follows

1.4 Pattern modifier: used in addition to regular delimiters to extend regular functions in matching, replacement, etc.

2. Regular expression function compatible with Perl

2.1 preg_match(string pattern,string subject[,array matches]): used to search and match strings. Parameter description:

Pattern is a regular pattern, subject is a string that needs to be processed, optional matches are used to save the matching results of each sub-pattern of pattern, matches[0] saves the overall content that matches pattern, matches[ 1] Saves the matched content in the first parentheses of pattern, and so on.

1:

);

<span id="lnum4">   4:</span><span> $subject = <span>"我的博客:http://www.ido321.com"</span>;</span>

<span id="lnum6">   6:</span><span>     <span>echo</span> <span>"搜索的URL是："</span>.$matches[0].<span>"<br/>"</span>;  <span>//数组第1个元素保存整个匹配结果</span></span>

;<span>//数组第2个元素保存第1个字表达式</span>

;<span>//数组第3个元素保存第2个字表达式</span>

;<span>//数组第4个元素保存第3个字表达式</span>

;<span>//数组第5个元素保存第4个字表达式</span>

<span id="lnum12">  12:</span><span> ?></span>

Results

    preg_match_all()与preg_match()函数类似，不同的是前者会一直匹配到字符串末尾，后者在第一次匹配后就停止匹配。

             2.2  preg_grep(string pattern,array iput)：匹配数组中的元素，返回与正则匹配的数组单元。参数说明：

                     pattern是正则，input是需要匹配的数组。

1:

<span id="lnum3">   3:</span><span> $version = preg_grep(<span>'/^[a-zA-Z]+(\d|\.)+$/'</span>,$arr);</span>

<span id="lnum5">   5:</span><span> <span>//输出：Array([1]=>Apache2.2.9 [2]=>MySQL5.0.51 [3]=>PHP5.2.6)</span></span>

<span id="lnum7">   7:</span><span> ?></span>

             2.3  preg_replace(mixed pattern,mixed replacement,mixed subject[,int limit])：字符串替换。说明：

                     该函数会在subject中搜索与pattern的匹配项，并用replacement替换。limit用于限制匹配的次数，即替换的次数。

1:

<span id="lnum3">   3:</span><span> $text = <span>'这个文本有<b>粗体</b>和<u>带有下划线</u>以及<i>斜体</i>'</span>;</span>

//将所有HTML标记替换为空

//值替换前2个HTML标记

              2.4  preg_split(string pattern,string subject[,int limit[,int flags]])：对字符串进行分割。说明：

 

                     函数返回一个数组。数组元素包含subject中与pattern匹配作为边界所分割的字符串，limit含义见2.3，flags含义请参考文档。

<span id="lnum2">   2:</span><span> <span>//按任数量的空格分割字符串</span></span>

<span id="lnum4">   4:</span><span>  </span>

<span id="lnum6">   6:</span><span> print_r($kerwords);</span>

来源：http://www.ido321.com/612.html

 

PHP中提取字符串--正则

$text = '

。。。。。。

test';

preg_match_all('/print_r($m);
 

php截取字符串的正则表达式，急

$s="soproxy.appspot.com/...opular";
preg_match('/v=(.*?)&/',$s,$matched);
echo($matched[1]);
 

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