Regular expression for url matching

I have a text field have value http://localhost/Send/test.php?s/?a=1&o=2. Another three text boxes. If we enter three values the above url will change like http://localhost/Sen开发者_如何学Pythond/test.php?s/?a=1&o=2&s1=a&s2=b&s3=c . The value for s1,s2 and s3 will not save anywhere. My question is how we check is the value for s1 is already set? And how can I update the value of s1 if iI change the textbox value for s1

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You can replace using this regex

url.replace(/&s1=([^$]+|[^&]+)/i, "&s1=newvalue");

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I guest you use PCRE in PHP:

(?=(?P<ES1>.*&s1=)?)(?(ES1)RegexToMatchIfS1AlreadyExist|RegexToMatchIfS1NotExist)

So

$result = preg_replace('/^(?=(?P<ES1>.*&s1=)?)(?(ES1)(?P<Left>.*&s1=)(?P<Right>.*+)$|RegexToMatchIfS1NotExist)/', '${1}newvalue${2}', ...);

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use this secure regular expression for every language...

^(https?|ftp)\:\/\/([a-z0-9+!*(),;?&=\$_.-]+(\:[a-z0-9+!*(),;?&=\$_.-]+)?@)?[a-z0-9+\$_-]+(\.[a-z0-9+\$_-]+)*(\:[0-9]{2,5})?(\/([a-z0-9+\$_-]\.?)+)*\/?(\?[a-z+&\$_.-][a-z0-9;:@/&%=+\$_.-]*)?(#[a-z_.-][a-z0-9+\$_.-]*)?\$