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I have a web crawler that picks up links from websites,.
I wanted a regular expression that matches the found links. And only links like these would pass.
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There are some means of doing that which you mentioned in the question, you can only capture the links that do not have the characters you mentioned (!#) or ignore the link if the character you want is captured.
As I do not know the operation of your application I will leave the 2 ways here and as you did not mention the Flavour of Regex nor the language it will be used I will assume that it is something like the Flavour pcre(php).
If you want to identify the strings that POSSESS # or ! use this pattern:
(?=.*#|.*!)(.*)
To get the result you want, you must identify all the matchs of that expression and disregard them, here’s a test I did to better visualize the result.
If you want to identify the strings that DO NOT POSSESS the standard:
((?!=.*#|.*!)(.*))
In that case you should consider only the matchs and disregard the chains that were not captured, here another test but with that expression.
Explanation:
The two regex function similarly, but in one, a Positive Lookahead (?=) and in the other the Negative Lookahead (?!=).
Lookahead is a token that performs a character string analysis and only returns if there is a specific pattern.
After that there is the string that will determine the condition for Lookahead (.*#|.*!), it indicates that there will be a string that can be numbers letters or symbols and after that # or !.
In the end there is (.*) that will capture all characters (if Positive Lookahead) or not (if Negative Lookahead).
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I don’t think that’s possible. Do you have any pattern about the links? Which ones you wouldn’t like to see?
– Paulo Martins
Would you like urls containing ? # and other characters not to be captured.
– Jeferson Mota
Jeferson, people are here to help you solve a problem, not to do something for free for you. Then put the code you are writing and take your doubts about it.
– RFL