I have regular expression that's is removing all url from a string but I want to change this and add exception for my site link.
$url = 'This is url for example to remove www.somewbsite.com but i want to skip removing this url www.mywebsite.com';
$no_url = preg_replace("/(https|http|ftp)\:\/\/|([a-z0-9A-Z]+\.[a-z0-9A-Z]+\.[a-zA-Z]{2,4})|([a-z0-9A-Z]+\.[a-zA-Z]{2,4})|\?([a-zA-Z0-9]+[\&\=\#a-z]+)/i", "★", $url);
First of all, since you are replacing with a hard-coded symbol, and you are using a case-insensitive modifier, your regex can be reduced to
'~(?:https?|ftp)://|(?:[a-z0-9]+\.)?[a-z0-9]+\.[a-z]{2,4}|\?[a-z0-9]+[&=#a-z]+~i'
whatever it means to match. Note that 2 alternatives here were too similar ([a-z0-9A-Z]+\.[a-z0-9A-Z]+\.[a-zA-Z]{2,4})|([a-z0-9A-Z]+\.[a-zA-Z]{2,4}), they are merged into 1 with the help of an optional non-capturing group ((?:[a-z0-9]+\.)?).
Now, if you want to avoid matching a specific pattern, you may use a SKIP-FAIL technique: match what you want to preserve and skip it.
'~www\.mywebsite\.com(*SKIP)(*FAIL)|(?:https?|ftp)://|(?:[a-z0-9]+\.)?[a-z0-9]+\.[a-z]{2,4}|\?[a-z0-9]+[&=#a-z]+~i'
See this regex demo.
