I have several proxy rule files for Squid, and all contain rules like:
acl blacklisted dstdom_regex ^.*facebook\.* ^.*youtube\.* ^.*games.yahoo.com\.*
The patterns match against the domain name: dstdom_regex means destination (server) regular expression pattern matching.
The objective is to block some websites, but I don't know by what method: domain name, keywords in the domain name, ...
Let's expand/describe the pattern:
^.*stackexchange\.* The whole pattern
^ String beginning
.* Match anything (greedy quantifier, I presume)
stackexchange Keyword to match
\.* Any number of dots (.)
Totally legitimate matches:
stackexchange.com: The Stack Exchange website.
stackoverflow.stackexchange: The imaginary Stack Exchange gTLD.
But these possible matches make it seem more like a keyword block:
stackexchange
stackexchanger
notstackexchange
not-stackexchange
some-website.stackexchange
some-website.stackexchange-tld
And the pattern seems to contain a bug, since it allows the following invalid cases to match, thanks to the \.* at the end, although they never naturally occur:
stackexchange.
stackexchange...
stackexchange..........
stackexchange.......com
stackexchange.com
stackexchangecom
you get the idea.
Anything containing stackexchange, even if separated by dots from everything else, is still a valid match.
So now, the question itself:
This all means that this is simply a match for stackexchange! (I'm assuming the original author didn't intend to match infinite dots.)
So why not just use the pattern stackexchange? Wouldn't it be faster and give the same results, except for the "bug" (\.*)?
I.e., isn't ^.*stackexchange equivalent to stackexchange?
Edit: Just to clarify, I didn't write those proxy rule files.
I don't understand why you use \.* to match all the following dots
However to bypass your problem you can try this out :
^[^\.]*\.stackexchange\.*
[^\.]* matches anything except a dot
\. then you match the dot
edit : formatting
Related
I need to find all email addresses with an arbitrary number of alphanumeric words, separated through a period. To test the regex, I'm using the website https://regex101.com/.
The structure of a valid email addresses is word1.word2.wordN#word1.word2.wordN.word.
The regex /[a-zA-Z0-9.]+#[a-zA-Z0-9.]+.[a-zA-Z0-9]+/gm finds all email addresses included in the document string, but also includes invalid addresses like ........#....com, if present.
I tried to group the repeating parts by using round brackets and a Kleene star, but that causes the regex engine to collapse.
Invalid regex:
/([a-zA-Z0-9]+.?)*[a-zA-Z0-9]+#([a-zA-Z0-9]+.?)*[a-zA-Z0-9]+.[a-zA-Z0-9]+/gm
Although there are many posts concerning regex groups, I was unable to find an explanation, why the regex engine fails. It seems that the engine gets stuck, while trying to find a match.
How can I avoid this problem, and what is the correct solution?
I think the main issue that caused you troubles is:
. (outside of []) matches any character,you probably meant to specify \. instead (only matches literal dot character).
Also there is no need to make it optional with ?, because the non-dot part of your regex will just match with the alphanumerical characters anyway.
I also reduced the right part (x*x is the same as x+), added a case-insensitive flag and ended up with this:
/([a-z0-9]+\.)*[a-z0-9]+#([a-z0-9]+\.)+[a-z0-9]+/gmi
I want to exclude common punctuation from my URL Regex detector when my clients type a sentence with a URL in it. A common scenario would be the URL example.com?q=this (which obviously needs to include the ?) versus a sentence saying
What do you think of example.com?
This expression suits my needs just fine:
(?:https?\:\/\/)?(?:\w+\.)+\w{2,}(?:[?#/]\S*)?
However it includes all punctuation at the end, so I am iterating through each match to find and use this captured group to exclude said punctuation:
(.*?)[?,!.;:]+$
However, I'm not sure how to leverage the "end of string" technique when scanning the entire block of text which may have multiple URLs. Was hoping there'd be a way to capture the right blocks from the get-go without the extra work.
Just require non-whitespace after the punctuation instead of making it optional.
(?:https?\:\/\/)?(?:\w+\.)+\w{2,}(?:[?#\/]\S+)?
You will of course lose valid ending of URLs like example.com/ will become example.com but as far as I know there is no difference.
I'm totally lost. I need a regular expression that
can detect any of the 4 starting urls like below
^(.*http://.*|.*http%3A%2F%2F.*|.*https://.*|.*https%3A%2F%2F.*)$
And ... .
should detect:
(any punctuation or space or backspace)(3 times the letter w in upper or lower case)(one dot)(anything)
And ... . which is important
Should Ignore, but NOT Exclude... . the following exact string (either it's present in the page or not)
http://www.w3.org
Which is complicated for me, because i still need to include it in the regex line
even if it's ignored, otherwise, it will match & be found in
(.*http://.*|.*http%3A%2F%2F.*|.*https://.*|.*https%3A%2F%2F.*)
And my aim is to find/match any url besides
http://www.w3.org
even if it's in the page, Or if it's not present.
so if there's only this in the page:
http://www.w3.org
& no other url.. then it shouldn't match.
Thanks Tyler but my regex knowledge is almost zero, i can only know what commands do when i right click on them to chose actions like in regulazy or regexr ((
So i updated my command according to the url i provided to you:
href%3D%22http%3A%2F%2Fwww%2Edommermuth%2D1%2Ecom
& it works:
https?(://|%3A%2F%2F)(?!www.w3.org)(.*)
But because of my lack of knowledge, i don't understand how to do that below
"What you could do is make the http part optional, or must match http or www or both. This type of regex came up in another question I answered recently - Multiple preg_replace RegEx for different URLs"
I tried to add this, but it doesn't work:
(www.)
All i'm missing now is detection of urls starting with www
(any punctuation or space or backspace)(3 times the letter w in upper or lower case)(one dot)(anything till it reaches a space or the end of a line)
OK so try this:
/\bhttps?(://|%3A%2F%2F)(?!www\.w3\.org)(.*)\b/g
Test here: http://regexr.com?38jp5
That test link uses javascript-style regex, but should work elsewhere.
The important part is the second half - a negative lookahead, that checks what follows is not the exact text www.w3.org
I compressed what you had: mine matches http then an optional s then either :// or %3A%2F%2F.
I wrapped the whole thing in word boundaries, you could change that to quotes or whatever you need. The global flag lets you match multiple items.
In regards to OP's questions:
D%22
could appear before http or https
this one is missing & should match:
href%3D%22http%3A%2F%2Fwww%2Edommermuth%2D1%2Ecom
If this matters, just remove the word boundary \b before and after the regex, so the http can match anywhere.
The regex command should detect: (any punctuation or space or backspace)(3 times the letter w in upper or lower case)(one dot)(anything)
This regex would fail to match a link like http://google.com - looking for www is really not a good way to check for a link on its own. What you could do is make the http part optional, or must match http or www or both. This type of regex came up in another question I answered recently - Multiple preg_replace RegEx for different URLs
Edit #2:
(any punctuation or space or backspace)(3 times the letter w in upper or lower case)(one dot)(anything till it reaches a space or the end of a line)
As I mention above, what you are describing will not match a url like http://google.com - but if that is what you want, use this:
(\W|^)[wW]{3}\.[^\s$]+
Instead of that, what I think you want is this, which is a combination of my first answer, and the link to a different post above.
((https?(://|%3A%2F%2F))(www\.)|(https?(://|%3A%2F%2F))|(www\.))(?!(www\.)?w3\.org)([^</\?\s]+)[^<\s]*
You'll want to use this regex with the Global and Insensitive flags
I have such txt file:
ххх.prontube.ru
salo.ru
bbb.antichat.ru
yyy.ru
xx.bb.prontube.ru
zzz.com
srfsf.jwbefw.com.ua
Trying to delete all subdomains with such regex:
Find: .+\.((.*?)\.(ru|ua|com\.ua|com|net|info))$
Replace with: \1
Receive:
prontube.ru
salo.ru
antichat.ru
yyy.ru
prontube.ru
zzz.com
com.ua
Why last line becomes com.ua instead of jwbefw.com.ua ?
This works without look around:
Find: [a-zA-Z0-9-.]+\.([a-zA-Z0-9-]+)\.([a-zA-Z0-9-]+)$
Replace: \1\.\2
It finds something with at least 2 periods and only letters, numbers, and dashes following the last two periods; then it replaces it with the last 2 parts. More intuitive, in my opinion.
There's something funny going on with that leading xxx. It doesn't appear to be plain ASCII. For the sake of this question, I'm going to assume that's just something funny with this site and not representative of your real data.
Incorrect
Interestingly, I previously had an incorrect answer here that accumulated a lot of upvotes. So I think I should preserve it:
Find: [a-zA-Z0-9-]+\.([a-zA-Z0-9-]+)\.(.+)$
Replace: \1\.\2
It just finds a host name with at least 2 periods in it, then replaces it with everything after the first dot.
The .+ part is matching as much as possible. Try using .+? instead, and it will capture the least possible, allowing the com.ua option to match.
.+?\.([\w-]*?\.(?:ru|ua|com\.ua|com|net|info))$
This answer still uses the specific domain names that the original question was looking at. As some TLD (top level domains) have a period in them, and you could theoretically have a list including multiple subdomains, whitelisting the TLD in the regex is a good idea if it works with your data set. Both current answers (from 2013) will not handle the difference between "xx.bb.prontube.ru" and "srfsf.jwbefw.com.ua" correctly.
Here is a quick explanation of why this psnig's original regex isn't working as intended:
The + is greedy.
.+ will zip all the way to the right at the end of the line capturing everything,
then work its way backwards (to the left) looking for a match from here:
(ru|ua|com\.ua|com|net|info)
With srfsf.jwbefw.com.ua the regex engine will first fail to match a,
then it will move the token one place to the left to look at "ua"
At that point, ua from the regex (the second option) is a match.
The engine will not keep looking to find "com.ua" because ".ua" met that requirement.
Niet the Dark Absol's answer tells the regex to be "lazy"
.+? will match any character (at least one) and then try to find the next part of the regex. If that fails, it will advance the token, .+ matching one more character and then evaluating the rest of the regex again.
The .+? will eventually consume: srfsf.jwbefw before matching the period, and then matching com.ua.
But the implimentation of ? also creates issues.
Adding in the question mark makes that first .+ lazy, but then causes group1 to match bb.prontube.ru instead of prontube.ru
This is because that first period after the bb will match, then inside group 1 (.*?) will match bb.prontube. before \.(ru|ua|com\.ua|com|net|info))$ matches .ru
To avoid this, change that third group from (.*?) to ([\w-]*?) so it won't capture . only letters and numbers, or a dash.
resulting regex:
.+?\.(([\w-])*?\.(ru|ua|com\.ua|com|net|info))$
Note that you don't need to capture any groups other than the first. Adding ?: makes the TLD options non-capturing.
last change:
.+?\.([\w-]*?\.(?:ru|ua|com\.ua|com|net|info))$
Search what: .+?\.(\w+\.(?:ru|com|com\.au))
Replace with: $1
Look in the picture above, what regex capture referring
It's color the way you will not need a regex explaination anymore ....
This is a bit hard to sum up in a title, but here is my problem:
(?:(?:http|https):\\/\\/)?(?:\\/\\/www\\.)?youtube.com\\/watch\\?(?:.*)v=(\\w{11}).*
Given the expression given below, I really really don't understand why ftp://www.youtube.com/watch?v=F5eScJmYZZ8 matches. I unsuccessfully tried to add ^ to the expression beginning, but then, my expression does not match anything anymore (this is done in Java, that explains the doubled backslashes).
How can ftp be accepted as it is clearly not listed in (http|ftp)?
EDIT
To be accurate, here is what is allowed:
http(s)://www.[...]
http(s)://[...]
www.[...]
[...]
and nothing else.
Because ? after the http part the means that it is optional. Use + instead of ?.
Also, you are checking for // after http twice.
\s* allows whitespace at the beginning. If you don't want to allow whitespace (i.e., the input text will contain only 1 match), use ^ instead.
Here is the working regex that meets all of your added requirements:
\s*(?:(http|https)\:\/\/)?(?:www\.)?youtube.com\/watch\?(?:.*)v=(\w{11}).*
Because the leading (?:(?:http|https):\\/\\/)? is optional. That's what the question mark at the end of the group signifies (match at most one, i.e. match only if it exists).
A leading ^ should prevent the match with ftp though. Can you post the failing regex you tried (with the ^)?
UPDATE:
Aha! It matches without the ^ since the http group is optional, and anything can come before the match (e.g. cheeseyoutube.com/... would match). Adding a ^ to the beginning of the regex fixes this, but there's another problem with your regex: the www group is trying to match two slashes (as first pointed out in Justin's answer), which it can't once the http group has already matched those slashes. So the www group fails to match (fine, since it's optional), but then the youtube part can't match since there's an unmatched www in the way!
This should fix your problem:
^(?:(?:http|https):\\/\\/)?(?:www\\.)?youtube.com\\/watch\\?(?:.*)v=(\\w{11}).*