php警告：preg_match（）[function.preg-match]：第71行的/sample.php中的未知修饰符'['[重复]

I am getting the error:

Warning: preg_match() [function.preg-match]: Unknown modifier '[' in /sample.php on line 71

Every time I'm try to run my script.

The code at line 71 is:

if(!preg_match("[h][t][t][p][:][/][/][a-zA-Z0-9\]",$link))

Please help me in fixing this issue..

</div>

You need delimiters and few modifications in pattern:

preg_match("/http:\/\/[a-zA-Z0-9\\\\]/",$link)

1. Missing delimeters for pattern : /pattern/
2. No need of too many [ ]
3. If you need \, you should escape with \ so \\\\ [Read this SO answer to know why you need three backslash to escape a backslash]

Your regex is overly complex (and lacking delimiters, which is your main issue). To match a literal character you don't need a character class, unless it is a special character (also depending on the character might still need to be escaped or positioned differently), a range of characters, or multiple alternative characters.

e.g.

[aeiou]

would allow for a vowel,

[aeiou]+

would allow for multiple vowels.

This regex:

~http://[a-zA-Z0-9]~

Should match http:// and then an alphanumerical character. The ~s are delimiters.

PHP usage:

if(!preg_match('~http://[a-zA-Z0-9]~',$link))