URI 是 Web上可用的每种资源 - HTML文档、图像、视频片段、程序等 - 由一个通用资源标志符（Uniform Resource Identifier, 简称"URI"）进行定位.

对就分组:

1. ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(?([^#]*))?(#(.*))?
2. 12 3 4 5 6 7 8 9

例,代码如下:

正则表达式 (http|ftp|https)://[w-_]+(.[w-_]+)+([w-.,@?^=%&:/~+#]*[w-@?^=%&/~+#])?

匹配 http://regxlib.com/Default.aspx | http://electronics.cnet.com/electronics/0-6342366-8-8994967-1.html

不匹配 www.phpfensi.com

正则表达式 ^\{2}[w-]+\(([w-][w-s]*[w-]+[$$]?$)|([w-][$$]?$))

正则表达式 ^(http|https|ftp)://([a-zA-Z0-9.-]+(:[a-zA-Z0-9.&%$-]+)*@)?((25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])|([a-zA-Z0-9-]+.)*[a-zA-Z0-9-]+.[a-zA-Z]{2,4})(:[0-9]+)?(/[^/][a-zA-Z0-9.,?'\/+&%$#=~_-@]*)*$

匹配 http://www.sysrage.net | https://64.81.85.161/site/file.php?cow=moo's |ftp://user:pass@host.com:123

不匹配 phpfensi.com

正则表达式 ^([a-zA-Z]:|\\[^/\:*?"<>|]+\[^/\:*?"<>|]+)(\[^/\:*?"<>|]+)+(.[^/\:*?"<>|]+)$

匹配 c:Test.txt | \serversharedTest.txt | \serversharedTest.t

不匹配 c:Test | \servershared | \serversharedTest.?

正则表达式 ^(http|https|ftp)://([a-zA-Z0-9.-]+(:[a-zA-Z0-9.&amp;%$-]+)*@)*((25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])|localhost|([a-zA-Z0-9-]+.)*[a-zA-Z0-9-]+.(com|edu|gov|int|mil|net|org|biz|arpa|info|name|pro|aero|coop|museum|[a-zA-Z]{2}))(:[0-9]+)*(/($|[a-zA-Z0-9.,?'\+&amp;%$#=~_-]+))*$

匹配 http://site.com/dir/file.php?var=moo | https://localhost |ftp://user:pass@site.com:21/file/dir

不匹配 site.com | http://site.com/dir//

正则表达式 ^([a-zA-Z]:)(\[^\/:*?<>"|]*(?<![ ]))*(.[a-zA-Z]{2,6})$

匹配 C:di___rfi_sysle.txt | c:dirfilename.txt

不匹配 c:dirfile?name.txt

正则表达式 ^([a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?.)+[a-zA-Z]{2,6}$

匹配 regexlib.com | this.is.a.museum | 3com.com

不匹配 notadomain-.com | helloworld.c | .oops.org

正则表达式 ^(((ht|f)tp(s?))://)?(www.|[a-zA-Z].)[a-zA-Z0-9-.]+.(com|edu|gov|mil|net|org|biz|info|name|museum|us|ca|uk)(:[0-9]+)*(/($|[a-zA-Z0-9.,;?'\+&amp;%$#=~_-]+))*$

匹配 www.blah.com:8103 | www.blah.com/blah.asp?sort=ASC |www.blah.com/blah.htm#blah

不匹配 www.state.ga | http://www.blah.ru

正则表达式 b(([w-]+://?|www[.])[^s()<>]+(?:([wd]+)|([^[:punct:]s]|/)))

匹配 http://foo.com/blah_blah | http://foo.com/blah_blah/ | (Something like http://foo.com/blah_blah) | http://foo.com/blah_blah_(wikipedia) | (Something like http://foo.com/blah_blah_(wikipedia)) | http://foo.com/blah_blah. |http://foo.com/blah_blah/. | <http://foo.com/blah_blah> | <http://foo.com/blah_blah/>| http://foo.com/blah_blah, | http://www.example.com/wpstyle/?p=364. | http://?df.ws/123 | rdar://1234 | rdar:/1234 | http://userid:password@example.com:8080 |http://userid@example.com | http://userid@example.com:8080 |http://userid:password@example.com

不匹配 no_ws.example.com | no_proto_or_ws.com | /relative_resource.php

可以匹配任何网址,代码如下:

1. <script type="text/javascript">
2. function IsURL(urlString)
3. {
4. regExp = /^((https?|ftp|news)://)?([a-z]([a-z0-9-]*[.。])+([a-z]{2}|aero|arpa|biz|com|coop|edu|gov|info|int|jobs|mil|museum|name|nato|net|org|pro|travel)|(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]).){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]))(/[a-z0-9_-.~]+)*(/([a-z0-9_-.]*)(?[a-z0-9+_-.%=&]*)?)?(#[a-z][a-z0-9_]*)?$/
5. if (urlString.match(regExp))
6. return "is a url";
7. else
8. return "not a url";
9. }
10. url = "";
11. alert(IsURL(url));
12. </script>

PHP 测试,代码如下:

1. <?php
2. $search = '~^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(?([^#]*))?(#(.*))?~i';
3. $url = 'http://www.php.net/pub/ietf/uri/#Related';
4. $url = trim($url);
5. preg_match_all($search, $url ,$rr);
6. printf("<p>输出URL数据为：</p><pre>%s</pre>n",var_export( $rr ,TRUE));
7. /*
8. 各分组如下
9. $1 = http:
10. $2 = http
11. $3 = //www.php.net
12. $4 = www.php.net
13. $5 = /pub/ietf/uri/
14. $6 = <undefined>
15. $7 = <undefined>
16. $8 = #Related
17. $9 = Related
18. */
19. ?>

百度上看到另外一块简洁的代码:

1. <?php
2. // 从 URL 中取得主机名
3. preg_match("/^(http://)?([^/]+)/i", "http：//www.php.net/index.html", $matches);
4. $host = $matches[2];
5. // 从主机名中取得后面两段
6. preg_match("/[^./]+.[^./]+$/", $host, $matches);
7. echo "domain name is: {$matches[0]}n";
8. ?>
9. //执行后输出：domain name is: php.net