Summary of examples of commonly used regular expression functions in PHP

1. preg_match()

Function prototype: int preg_match (string $pattern, string $content [, array $matches])
preg_match () function in $contentstring Search for content that matches the regular expression given by $pattern. If $matches is provided, the matching results are placed in it. $matches[0] will contain the text that matches the entire pattern, $matches[1] will contain the first captured match of the pattern element enclosed in parentheses, and so on. This function only performs one match and ultimately returns the number of matching results of 0 or 1. Listing 6.1 shows a code example for the preg_match() function.
Code 6.1 Date and time matching
The code is as follows:

<?php 
//需要匹配的字符串。date函数返回当前时间 
$content = "Current date and time is ".date("Y-m-d h:i a").", we are learning PHP together."; 
//使用通常的方法匹配时间 
if (preg_match ("//d{4}-/d{2}-/d{2} /d{2}:/d{2} [ap]m/", $content, $m)) 
{ 
echo "匹配的时间是：" .$m[0]. "/n"; 
} 
//由于时间的模式明显，也可以简单的匹配 
if (preg_match ("/([/d-]{10}) ([/d:]{5} [ap]m)/", $content, $m)) 
{ 
echo "当前日期是：" .$m[1]. "/n"; 
echo "当前时间是：" .$m[2]. "/n"; 
} 
?>

This is a simple dynamic text string matching example. Assuming that the current system time is "13:25 on August 17, 2016", the following content will be output.
The matching time is: 2016-08-17 01:25 pm
The current date is: 2016-08-17
The current time is: 01:25 pm

2 ． ereg() and eregi()

ereg() is the matching function for regular expressions in the POSIX extension library. eregi() is a case-ignoring version of the ereg() function. Both have similar functions to preg_match, but the function returns a Boolean value indicating whether the match was successful or not. It should be noted that the first parameter of the POSIX extension library function accepts a regular expression string, that is, no delimiter is required. For example, Listing 6.2 is a method for checking the security of file names.
Code 6.2 Security check of file name
The code is as follows:

<?php 
$username = $_SERVER[&#39;REMOTE_USER&#39;]; 
$filename = $_GET[&#39;file&#39;]; 
//对文件名进行过滤，以保证系统安全 
if (!ereg(&#39;^[^./][^/]*$&#39;, $userfile)) 
{ 
die(&#39;这不是一个非法的文件名！&#39;); 
} 
//对用户名进行过滤 
if (!ereg(&#39;^[^./][^/]*$&#39;, $username)) 
{ 
die(&#39;这不是一个无效的用户名&#39;); 
} 
//通过安全过滤，拼合文件路径 
$thefile = "/home/$username/$filename"; 
?>

Normally, using the Perl-compatible regular expression matching function perg_match() will be better than using ereg() or eregi( ) is faster. If you just want to find whether a string contains a certain substring, it is recommended to use the strstr() or strpos() function.

Replacement of regular expressions

1． ereg_replace() and eregi_replace()

Function prototype: string ereg_replace (string $pattern, string $replacement, string $string)
string eregi_replace (string $pattern, string $replacement , string $string)
ereg_replace() searches the pattern string $pattern in $string and replaces the matched result with $replacement. When $pattern contains pattern units (or sub-patterns), positions in $replacement such as "/1" or "$1" will be replaced by the content matched by these sub-patterns. And "/0" or "$0" refers to the content of the entire matching string. It should be noted that the backslash is used as an escape character in double quotes, so the form "//0" and "//1" must be used.
eregi_replace() and ereg_replace() have the same functions, except that the former ignores case. Code 6.6 is an application example of this function. This code demonstrates how to do simple cleaning work on the program source code.
Code 6.6 Cleaning up the source code
The code is as follows:

<?php 
$lines = file(&#39;source.php&#39;); //将文件读入数组中 
for($i=0; $i<count($lines); $i++) 
{ 
//将行末以“//”或“#”开头的注释去掉 
$lines[$i] = eregi_replace("(////|#).*$", "", $lines[$i]); 
//将行末的空白消除 
$lines[$i] = eregi_replace("[ /n/r/t/v/f]*$", "/r/n", $lines[$i]); 
} 
//整理后输出到页面 
echo htmlspecialchars(join("",$lines)); 
?>

2． preg_replace()

Function prototype: mixed preg_replace (mixed $pattern, mixed $replacement, mixed $subject [, int $limit])
preg_replace is more powerful than ereg_replace. The first three parameters can all use arrays; the fourth parameter $limit can set the number of replacements, and the default is to replace all. Code 6.7 is an application example of array replacement.
Code 6.7 Array replacement
The code is as follows:

<?php 
//字符串 
$string = "Name: {Name}<br>/nEmail: {Email}<br>/nAddress: {Address}<br>/n"; 
//模式 
$patterns =array( 
"/{Address}/", 
"/{Name}/", 
"/{Email}/" 
); 
//替换字串 
$replacements = array ( 
"No.5, Wilson St., New York, U.S.A", 
"Thomas Ching", 
"tom@emailaddress.com", 
); 
//输出模式替换结果 
print preg_replace($patterns, $replacements, $string); 
?>

The output results are as follows.

Name: Thomas Ching", 
Email: tom@emailaddress.com 
Address: No.5, Wilson St., New York, U.S.A

The pattern modifier "e" can be used in the regular expression of preg_replace. Its function is to use the matching result as an expression and can be re-operated. For example:
The code is as follows:

<?php 
$html_body = “<HTML><Body><H1>TEST</H1>My Picture<Img src=”my.gif”></Body></HTML>”; 
//输出结果中HTML标签将全部为小写字母 
echo preg_replace ( 
"/(<//?)(/w+)([^>]*>)/e", 
"&#39;//1&#39;.strtolower(&#39;//2&#39;).&#39;//3&#39;", //此处的模式变量//2将被strtolower转换为小写字符 
$html_body); 
?>

Tips
The preg_replace function uses Perl-compatible regular expression syntax and is usually a faster alternative than ereg_replace. If you only want to do a simple replacement of a string, you can use the str_replace function.

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