You may wonder how it works. I will try to explain how this should be done in various ways. First we start with how the regular expression works and how it is used.
Regex - regex
When calculating a regular expression (abbreviated regular expression or regular expression) is a sequence of characters that forms a search pattern, mainly for use in matching patterns with strings or matching strings, that is, "search and replace" similar operations.
Basic syntax
To use regular expressions, you first need to learn the syntax. This syntax consists of a series of letters, numbers, periods, hyphens, and special characters that we can group using different parentheses.
^ The circumflex symbol matches the beginning of the input string or line, although in some cases it can be omitted $ Same as with the circumflex symbol, the dollar sign matches the end of the input string or line . The period matches any single character ? It will match the preceding pattern zero or one times + It will match the preceding pattern one or more times * It will match the preceding pattern zero or more times | Boolean OR - Used when describing a range of elements () Groups pattern elements together [] Matches any single character between the square brackets {min, max} Used to match exact character counts, where min and max are integers \d Matches any single digit \D Matches any single non digit caharcter \w Matches any alpha numeric character including underscore (_) \W Matches any non alpha numeric character excluding the underscore character \s Matches any single whitespace character
Brackets
Brackets [] are of particular importance when used in the context of regular expressions. They are used to search for a range of characters.
[0-9] Matches any decimal digit from 0 through 9. [az] Matches any character from lowercase a through lowercase z. [AZ] Matches any character from uppercase A through uppercase Z. [aZ] Matches any character from lowercase a through uppercase Z.
<strong> Examples
Let's see how to use the operators correctly. We will do this with an example of the word hello .
/hello/ Matches the word hello /^hello/ Matches hello at the start of a string. Possible matches are hello or helloworld, but not worldhello /hello$/ Matches hello at the end of a string or line. /he.o/ Matches any character between he and o. Possible matches are helo or heyo, but not hello /he?llo/ Matches either hllo or hello /hello+/ Matches hello one or more times. Eg matches hello or hellohello /he*llo/ Matches llo, hello or hehello, but not hellooo /hello|world/ Matches either hello or world /(AZ)/ Using the hyphen character to denote a range, matches every uppercase character from A to ZEg A, B, C… /[abc]/ Matches any single character a, b or c /abc{1}/ Matches precisely one c character after the characters ab. Eg matches abc, but not abcc /abc{1,}/ Matches one or more c character after the characters ab. Eg matches abc or abcc /abc{2,4}/ Matches between two and four c character after the characters ab. Eg matches abcc, abccc or abcccc, but not abc
Most common
[^a-zA-Z] Matches any string not containing any of the characters ranging from a through z and A through Z. pp Matches any string containing p, followed by any character, in turn followed by another p. ^.{2}$ Matches any string containing exactly two characters. <b>(.*)</b> Matches any string enclosed within <b> and </b>. p(hp)* Matches any string containing ap followed by zero or more instances of the sequence hp.
Regex matches URL
First, let's see how the URL is created. We have only a few options:
http://example.com/https://example.com/ftp://example.com/www.example.comuser@example.com127.0.0.1http://example.com:8080/
http:// , https:// , ftp , www , mail , ip and port .
Method 1 (1/10 points)
// Only mails $match = preg_match('/[^\x00-\x20()<>@,;:\\".[\]\x7f-\xff]+(?:\.[^\x00-\x20()<>@,;:\\".[\]\x7f-\xff]+)*\@[^\x00-\x20()<>@,;:\\".[\]\x7f-\xff]+(?:\.[^\x00-\x20()<>@,;:\\".[\]\x7f-\xff]+)+/', $string, $array);
Method 2 (5/10 points)
// Without ports, www-s, ip-s and mails $text = ereg_replace("[[:alpha:]]+://[^<>[:space:]]+[[:alnum:]/]","<a href=\"\\0\">\\0</a>", $text);
Method 3 (10/10 points)
/* Proposed by: * Søren Løvborg * http://stackoverflow.com/users/136796/soren-lovborg */ $rexProtocol = '(https?://)?'; $rexDomain = '((?:[-a-zA-Z0-9]{1,63}\.)+[-a-zA-Z0-9]{2,63}|(?:[0-9]{1,3}\.){3}[0-9]{1,3})'; $rexPort = '(:[0-9]{1,5})?'; $rexPath = '(/[!$-/0-9:; =@ _\':;!a-zA-Z\x7f-\xff]*?)?'; $rexQuery = '(\?[!$-/0-9:; =@ _\':;!a-zA-Z\x7f-\xff]+?)?'; $rexFragment = '(#[!$-/0-9:; =@ _\':;!a-zA-Z\x7f-\xff]+?)?'; function callback($match) { // Prepend http:// if no protocol specified $completeUrl = $match[1] ? $match[0] : "http://{$match[0]}"; return '<a href="' . $completeUrl . '">' . $match[2] . $match[3] . $match[4] . '</a>'; } $text = preg_replace_callback("&\\b$rexProtocol$rexDomain$rexPort$rexPath$rexQuery$rexFragment(?=[?.!,;:\"]?(\s|$))&", 'callback', htmlspecialchars($text));
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