Develop Reference

Get all strings between triple Pipes, e.g. |||Hello|||, from a text

I wanted to get all strings, that are surrounded by triple pipes (like |||Hello|||) from a text and found this regex in C#:
Regex regex = new Regex(#".*?\|\|\|(\w+)\|\|\|"); // searches strings, which are surrounded by three pipes >>> |||string|||
foreach (Match match in regex.Matches(strContent))
{
lstReturn.Add(match.Groups[1].Value);
}
It works as it should with small strings, but not on a large text (freezes without response).
Can you please tell me how I can make this query faster or suggest an alternative?

The .*? at the start of your pattern makes matching slower since the engine needs to perform more checks once the subsequent subpatterns fail. Once there is no | the .*? is "expanded", or "backtracked", and the non-| char is matched with .*?. With very long strings, this leads to catastrophic backtracking.
The second pattern also allows for internal optimization since the regex engine knows the match will start with a | hardcoded char.
You need to remove .*? since you do not need the part before |||word|||.
You can compare .*?\|\|\|(\w+)\|\|\| and \|\|\|(\w+)\|\|\| matching steps:
First one:
Second one:
You can see that "red arrows" denoting backtracking fire more often in the first image.

How do I select all including sensitive case (regex) in c#?

I have a problem with a regex command,
I have a file with a tons of lines and with a lot of sensitive characters,
this is an Example with all sensitive case 0123456789/*-+.&é"'(-è_çà)=~#{[|`\^#]}²$*ù^%µ£¨¤,;:!?./§<>AZERTYUIOPMLKJHGFDSQWXCVBNazertyuiopmlkjhgfdsqwxcvbn
I tried many regex commands but never get the expected result,
I have to select everything from Example to the end
I tried this command on https://www.regextester.com/ :
\sExample(.*?)+
Image of the result here
And when I tried it in C# the only result I get was : Example
I don't understand why --'

Here's a quick chat about greedy and pessimistic:
Here is test data:
Example word followed by another word and then more
Here are two regex:
Example.*word
Example.*?word
The first is greedy. Regex will match Example then it will take .* which consumes everything all the way to the END of the string and the works backwards spitting a character at a time back out, trying to make the match succeed. It will succeed when Example word followed by another word is matched, the .* having matched word followed by another (and the spaces at either end)
The second is pessimistic; it nibbled forwards along the string one character at a time, trying to match. Regex will match Example then it'll take one more character into the .*? wildcard, then check if it found word - which it did. So pessimistic matching will only find a single space and the full match in pessimistic mode is Example word
Because you say you want the whole string after Example I recommend use of a greedy quantifier so it just immediately takes the whole string that remains and declares a match, rather than nibbling forwards one at a time (slow)
This, then, will match (and capture) everything after Example:
\sExample(.*)
The brackets make a capture group. In c# we can name the group using ?<namehere> at the start of the brackets and then everything that .* matches can be retrieved with:
Regex r = new Regex("\sExample(?<x>.*)");
Match m = r.Match("Exampleblahblah");
Console.WriteLine(m.Groups["x"].Value); //prints: blahblah
Note that if your data contains newlines you should note that . doesn't match a newline, unless you enable RegexOptions.SingleLine when you create the regex

Prevent Regex from devouring optional part of the match

I'v searched extensively but I can't find a simple answer to this and my Regex experience is limited. I'd appreciate a simple solution that is explained, please.
I have a very large string and I need to substitute certain words in it as follows:
Example: wherever you find the string "LINK-ABC" make it "LINK_ABC".
I wrote my Regex Match and Replace strings:
#"LINK-ABC", #"LINK_ABC" and it worked.
But there were a couple of things I had not recognized.
There COULD be words in the file like this:
LINK-ABC-DEF LINK-ABC-GHI-JKL ... and so on.
So I get "LINK_ABC-DEF" etc. (which is NOT what I want; this should have remained intact...)
Once I realized the problem it seemed that what I REALLY wanted was to recognize ONLY the word being matched and leave any cases where it was in combination with something else, unchanged. It seemed to me that if I checked for a space or period on the Match word, that should do it, so...
#"LINK-ABC[ |\\.]",#"LINK_ABC"
... and now I have stumbled.
Sample string:
link-xxx link-aaa-sss link-xxx-bbb link-xxx link-xxx.
Match/Replace string:
link-xxx[ |\\.],link_xxx
Result string:
link_xxxlink-aaa-sss link-xxx-bbb link_xxxlink_xxx
The replacements are correct, BUT the trailing comma or period has been "devoured" and so the result string is wrong.
Is there a way that I can match so that if it matches on space, the replacement will have a space and if it matches on a period, the replacement will have a period? I s'pose I could do 2 separate matches but I'd like to increase my understanding of Regex and do it more elegantly if it is possible.

You should be able to achieve the behavior you want with "capture groups"
var matchstring = #"link-xxx([ \.]|$)";
var fixstr = #"link_xxx$1";
The parenthesis around the last part of the matchstring will retain whatever matched inside it, and the $1 in the fixstr will substitute whatever was captured by that group.
I've also modified your punctuation section a little bit, presuming you want to replace a match if it happens to be the last word in the input (by adding the |$). A | inside a character class [] is a literal | character, so I removed it assuming you don't actually expect that in your input.

Removing comments using regex

I am building a parser, and I would like to remove comments from various lines. For example,
variable = "some//thing" ////actual comment
Comment marker is //. In this case, variable would contain "some//thing" and everything else would be ignored. I plan to do it using regex replace. Currently I am using (".*"|[ \t])*(\/\/.*) as regex. However replacing it replaces "some//thing" ////actual comment entirely.
I can not figure out the regex which I should use instead. Thanks for any help.
Additional info - I am using C# with netcoreapp 1.1.0
Edit - some cases might be of a line with just comment like //line comment. Strings also might contain escaped quotes.

Here is the ugly regex pattern. I believe it will work well. I have tried it with every pathological example I can think of, including lines that contain syntax errors. For example, a quoted string that has too many quotes, or too few, or has a double escaped quote, which is, therefore, not escaped. And with quoted strings in the comments, which I have been known to do when I want to remind myself of alternatives.
The only time that it trips up is if there is a double slash inside a seemingly quoted string and somehow that string is malformed and the double slash ends up legally outside the properly quoted portion. Syntactically that makes it a valid comment, even though not the programmer's intention. So, from the programmer's perspective it's wrong, but by the rules, it's really a comment. Meaning, the pattern only appears to trip up.
When used the pattern will return the non-comment portion of the line(s). The pattern has a newline \n in it to allow for applying it to an entire file. You may need to modify that if you system interprets newlines in some other fashion, for example as \r or \r\n. To use it in single line mode you can remove that if you choose. It is at characters 17 and 18 in the one-liner and is on the fifth line, 6th and 7th printing characters in the multi-line version. You can safely leave it there, however, as in single-line mode it makes no difference, and in multi-line mode it will return a newline for lines of code that are either blank, or have a comment beginning in the first column. That will keep the line numbers the same in the original version and the stipped version if you write the results to a new file. Makes comparison easy.
One major caveat for this pattern: It uses a grouping construct that has varying level of support in regex engines. I believe as used here, with a lookaround, it's only the .NET and PCRE engines that will accept it YMMV. It is a tertiary type: (?(_condition_)_then_|_else_). The _condition_ pattern is treated as a zero-width assertion. If the pattern matches, then the _then_ pattern is used in the attempted match, otherwise the _else_ pattern is used. Without that construct, the pattern was growing to uncommon lengths, and was still failing on some of my pathological test cases.
The pattern presented here is as it needs to be seen by the regex engine. I am not a C# programmer, so I don't know all the nuances of escaping quoted strings. Getting this pattern into your code, such that all the backslashes and quotes are seen properly by the regex engine is still up to you. Maybe C# has the equivalent of Perl's heredoc syntax.
This is the one-liner pattern to use:
^((?:(?:(?:[^"'/\n]|/(?!/))*)(?("(?=(?:\\\\|\\"|[^"])*"))(?:"(?:\\\\|\\"|[^"])*")|(?('(?=(?:\\\\|\\'|[^'])*'))(?:'(?:\\\\|\\'|[^'])*')|(?(/)|.))))*)
If you want to use the ignore pattern whitespace option, you can use this version:
(?x) # Turn on the ignore white space option
^( # Start the only capturing group
(?: # A non-capturing group to allow for repeating the logic
(?: # Capture either of the two options below
[^"'/\n] # Capture everything not a single quote, double quote, a slash, or a newline
| # OR
/(?!/) # Capture a slash not followed by a slash [slash an negative look-ahead slash]
)* # As many times as possible, even if none
(?(" # Start a conditional match for double-quoted strings
(?=(?:\\\\|\\"|[^"])*") # Followed by a properly closed double-quoted string
) # Then
(?:"(?:\\\\|\\"|[^"])*") # Capture the whole double-quoted string
| # Otherwise
(?(' # Start a conditional match for single-quoted strings
(?=(?:\\\\|\\'|[^'])*') # Followed by a properly closed single-quoted string
) # Then
(?:'(?:\\\\|\\'|[^'])*') # Capture the whole double-quoted string
| # Otherwise
(?([^/]) # If next character is not a slash
.) # Capture that character, it is either a single quote, or a double quote not part of a properly closed
) # end the conditional match for single-quoted strings
) # End the conditional match for double-quoted strings
)* # Close the repeating non-capturing group, capturing as many times as possible, even if none
) # Close the only capturing group
This allows for your code to explain this monstrosity so that when someone else looks at it, or in a few months you have to work on it yourself, there's no WTF moment. I think the comments explain it well, but feel free to change them any way you please.
As mentioned above, the conditional match grouping has limited support. One place it will fail is on the site you linked to in an earlier comment. Since you're using C#, I choose to do my testing in the .NET Regex Tester, which can handle those constructs. It includes a nice Reference too. Given the proper selections on the side, you can test either version above, and experiment with it as well. Considering its complexity, I would recommend testing it, somewhere, against data from your files, as well as any edge cases and pathological tests you can dream up.
Just to redeem this small pattern, there is a much bigger pattern for testing email address that is 78 columns by 81 lines, with a couple dozen characters to spare. (Which I do not recommend using, or any other regex, for testing email addresses. Wrong tool for the job.) If you want to scare yourself, have a peek at it on the ex-parrot site. I had nothing to do with that!!

"[^"\\]*(?:\\[\W\w][^"\\]*)*"|(\/\/.*)
Flags: global
Matches full strings or a comment.
Group 1: comment.
So if there's no comment, replace with the same matching text. Otherwise, do your thing on the comment itself.

RegEx pattern for partial URL (switch on two values in path)

I have a URL pattern that needs to contain either APPLES or ORANGES in it, no other value. Optionally, it can also have query parameters. I've tried a number of RegEx patterns, but I just can't get a pattern that will respect the strict match.
Sample URLs
Good
http://www.website.com/en/pages/APPLES
http://www.website.com/en/pages/APPLES?k=v
http://www.website.com/en/pages/ORANGES?k=v&k2=v2
http://www.website.com/en/pages/ORANGES
Bad
http://www.website.com/en/pages/APPLES???k=v
http://www.website.com/en/pages/APPLES?k=v=v
http://www.website.com/en/pages/APPLESORANGES
http://www.website.com/en/pages/1APPLES
http://www.website.com/en/APPLES
Attempted RegEx Patterns (well, at least the best attempts)
(http://*.*.website*.*.com/*.*/pages(/APPLES)|(/ORANGES)[\?]*.*)
(http://*.*.website*.*.com/*.*/pages(/APPLES|/ORANGES)[\?]*.*)
If you're curious, I intentionally want to allow any sub-domain, suffix after "website" (for different environments), and any path between .com/ and /pages, hence the use of . in a number of places.
What would be the best way to achieve this?
**Edit: Final Answer**
My final answer was merged from mathematical.coffee and fardjad.
^https?://.*\.website\b.*\.com/.*/pages/(APPLES\b|ORANGES\b)((\?\w+=\w+)(&?\w+=\w+)*)?$
The single limitation I've discovered is that it will not allow a few valid characters (.~_-%+) in the query string parameter key=value pairs (see: http://en.wikipedia.org/wiki/Query_string#Structure). This isn't an issue for me as I'm matching against a string returned from .NET's Uri class, so I know the URL is well-formed overall.

I think the *.* should be .*:
http://.*\.website\b.*\.com/.*/pages/PAGE[12](\?[^=]+=[^&=]+(&[^=]+=[^=&]+)*)?
Explanation:
http:// # just http://
.*\. # any thing, just make sure it's followed by '.'
website\b # website, the whole word
.*\.com # anything between website and .com
/.*/pages/ # anything between the .com and the pages
PAGE[12] # PAGE1 or PAGE2
(\? # opening bracket and '?' (query string)
[^=]+ # the key: i've said it can't include =
= # =
[^=&]+ # the value: i've said it can't include = or &
(& # opening bracket and '&' for next part of query string
[^=]+=[^=&]+ # key=value pair, same regex as before
)* # 0 or more of these (the &key=value)
)? # the entire query string is optional.
NOTE - there are usually problems parsing query strings with regex and making sure it's a syntactically valid regex.
For example, in the regex I supplied above, I've said that the value in &key=value can't have an ampersand in it. But it could be an escaped entity, like &, which is legal.
You'll always suffer from this sort of problem when you try to parse syntax with regex. It's a risk you'll have to take.
Alternatively, I am sure there is a C# module to parse URLs (many other languages have these), and they take care of all these special cases for you.

Try this:
^https?://(www\.)?\w+[^/]+(/\w+(?=/)){2}/(PAGE1|PAGE2)((\?\w+=\w+)(&?\w+=\w+)*)?$