I'm trying to come up with a validation expression to prevent users from entering html or javascript tags into a comment box on a web page.
The following works fine for a single line of text:
^(?!.*(<|>)).*$
..but it won't allow any newline characters because of the dot(.). If I go with something like this:
^(?!.*(<|>))(.|\s)*$
it will allow multiple lines but the expression only matches '<' and '>' on the first line. I need it to match any line.
This works fine:
^[-_\s\d\w"'\.,:;#/&\$\%\?!#\+\*\\(\)]{0,4000}$
but it's ugly and I'm concerned that it's going to break for some users because it's a multi-lingual application.
Any ideas? Thanks!
Note that your RE prevents users from entering < and >, in any context. "2 > 1", for example. This is very undesirable.
Rather than trying to use regular expressions to match HTML (which they aren't well suited to do), simply escape < and > by transforming them to < and >. Alternatively, find a package for your language-of-choice that implements whitelisting to allow a limited subset of HTML, or that supports its own markup language (I hear markdown is nice).
As for "." not matching newline characters, some regexp implementations support a flag (usually "m" for "multi-line" and "s" for "single line"; the latter causes "." to match newlines) to control this behavior.
The first two are basically equivalent to /^[^<>]*$/, except this one works on multiline strings. Any reason why you didn't write the RE that way?
So, I looked into it and there is a .Net 'SingleLine' option for regular expressions that causes "." to also match on the new line character. Unfortunately, this isn't available in the ASP.Net RegularExpressionValidator. As far as I can see, there's no way to make something like ^(?!.(<\w+>)).$ work on a multi-line textbox without doing server-side validation.
I took your advice and went the route of escaping the tags on the server side. This requires setting the validation page directive to 'false' but in this particular instance that isn't a big deal because the comment box is really the only thing to worry about.
Related
Regex noob here struggling with this, which I know it will be easy for some of you regex gods out there!
Given the following:
title: Some title
date: 2022-08-15
tags: <value to extract>
identifier: 1234567
---------------------------
Some text
some more text
I would like a regex to match everything except the value of tags (ie the "<value to extract>" text).
For context, this is supposed to run on emacs (in case it matters).
EDIT: Just to clarify as per #phils question, all I care about extracting the tags value. However, this is via a package setting that asks for a regex string and I don't have much control over how it gets use. It seems to expect a regex to strip what I don't need from the string rather than matching what I do want, which is slightly annoying.. Also, the since it seems to match everything with \\(.\\), I'm guessing it's using the global flag?
Please let me know if any of this isn't clear.
Emacs regular expressions can't trivially express "not foo" for arbitrary values of foo. (The likes of PCRE have non-regular extensions for zero-width negative look-ahead/behind assertions, but in Emacs that sort of functionality is generally done with the support of lisp code1.)
You can still do it purely with regexp matching, but it's simply very cumbersome. An Emacs regexp which matches any line which does not begin with tags: is:
^\(?:$\|[^t]\|t[^a]\|ta[^g]\|tag[^s]\|tags[^:]\).*
or if you need to enter it in the elisp double-quoted read syntax for strings:
"^\\(?:$\\|[^t]\\|t[^a]\\|ta[^g]\\|tag[^s]\\|tags[^:]\\).*"
1 In lisp code you would instead simply check each line to see whether it does start with tags: and, if so, skip it (which is why Emacs generally gets away without the feature you're looking for, but of course that doesn't help you here).
After playing around with it for a bit and taken inspiration from #phils' answer, I've come up with the following:
"^\\(?:\\(#\\+\\)?\\(?:filetags:\s+\\|tags:\s+\\|title:.*\\|identifier:.*\\|date:.*\\)\\|.*\\)"
I've also added an extra \\(#\\+\\)? to account for org meta keys which would usually have the format #+key: value.
I am currently learning regex and I am trying to filter all links (eg: http://www.link.com/folder/file.html) from a document with notepad++. Actually I want to delete everything else so that in the end only the http links are listed.
So far I tried this : http\:\/\/www\.[a-zA-Z0-9\.\/\-]+
This gives me all links which is find, but how do I delete the remaining stuff so that in the end I have a neat list of all links?
If I try to replace it with nothing followed by \1, obviously the link will be deleted, but I want the exact opposite to have everything else deleted.
So it should be something like:
- find a string of numbers, letters and special signs until "http"
- delete what you found
- and keep searching for more numbers, letters ans special signs after "html"
- and delete that again
Any ideas? Thanks so much.
In Notepad++, in the Replace menu (CTRL+H) you can do the following:
Find: .*?(http\:\/\/www\.[a-zA-Z0-9\.\/\-]+)
Replace: $1\n
Options: check the Regular expression and the . matches newline
This will return you with a list of all your links. There are two issues though:
The regex you provided for matching URLs is far from being generic enough to match any URL. If it is working in your case, that's fine, else check this question.
It will leave the text after the last matched URL intact. You have to delete it manually.
The answer made previously by #psxls was a great help for me when I have wanted to perform a similar process.
However, this regex rule was written six years ago now: accordingly, I had to adjust / complete / update it in order it can properly work with the some recent links, because:
a lot of URL are now using HTTPS instead of HTTP protocol
many websites less use www as main subdomain
some links adds punctuation mark (which have to be preserved)
I finally reshuffle the search rule to .*?(https?\:\/\/[a-zA-Z0-9[:punct:]]+) and it worked correctly with the file I had.
Unfortunately, this seemingly simple task is going to be almost impossible to do in notepad++. The regex you would have to construct would be...horrible. It might not even be possible, but if it is, it's not worth it. I pretty much guarantee that.
However, all is not lost. There are other tools more suitable to this problem.
Really what you want is a tool that can search through an input file and print out a list of regex matches. The UNIX utility "grep" will do just that. Don't be scared off because it's a UNIX utility: you can get it for Windows:
http://gnuwin32.sourceforge.net/packages/grep.htm
The grep command line you'll want to use is this:
grep -o 'http:\/\/www.[a-zA-Z0-9./-]\+\?' <filename(s)>
(Where <filename(s)> are the name(s) of the files you want to search for URLs in.)
You might want to shake up your regex a little bit, too. The problems I see with that regex are that it doesn't handle URLs without the 'www' subdomain, and it won't handle secure links (which start with https). Maybe that's what you want, but if not, I would modify it thusly:
grep -o 'https\?:\/\/[a-zA-Z0-9./-]\+\?' <filename(s)>
Here are some things to note about these expressions:
Inside a character group, there's no need to quote metacharacters except for [ and (sometimes) -. I say sometimes because if you put the dash at the end, as I have above, it's no longer interpreted as a range operator.
The grep utility's syntax, annoyingly, is different than most regex implementations in that most of the metacharacters we're familiar with (?, +, etc.) must be escaped to be used, not the other way around. Which is why you see backslashes before the ? and + characters above.
Lastly, the repetition metacharacter in this expression (+) is greedy by default, which could cause problems. I made it lazy by appending a ? to it. The way you have your URL match formulated, it probably wouldn't have caused problems, but if you change your match to, say [^ ] instead of [a-zA-Z0-9./-], you would see URLs on the same line getting combined together.
I did this a different way.
Find everything up to the first/next (https or http) (then everything that comes next) up to (html or htm), then output just the '(https or http)(everything next) then (html or htm)' with a line feed/ carriage return after each.
So:
Find: .*?(https:|http:)(.*?)(html|htm)
Replace with: \1\2\3\r\n
Saves looking for all possible (incl non-generic) url matches.
You will need to manually remove any text after the last matched URL.
Can also be used to create url links:
Find: .*?(https:|http:)(.*?)(html|htm)
Replace: \1\2\3\r\n
or image links (jpg/jpeg/gif):
Find: .*?(https:|http:)(.*?)(jpeg|jpg|gif)
Replace: <img src="\1\2\3">\r\n
I know my answer won't be RegEx related, but here is another efficient way to get lines containing URLs.
This won't remove text around links like Toto mentioned in comments.
At least if there is nice pattern to all links, like https://.
CTRL+F => change tab to Mark
Insert https://
Tick Mark to bookmark.
Mark All.
Find => Bookmarks => Delete all lines without bookmark.
I hope someone who lands here in search of same problem will find my way more user-friendly.
You can still use RegEx to mark lines :)
There are tons of solutions to find and/or parse normal URLs, but none of them deals with arbitrary text, i.e. URLs that are split over several lines? How would you find a URL that can have line breaks after any character?
Note: I'm not interested in the individual parts of the URL. I just want to find all URLs in a given text to convert them to links (e.g. like in plain e-mail text).
Example:
Text text text text text. Look at this:
http://stackoverfl
ow.com/
questions/15252042/
find-urls-in-text
Question question question.
Several approaches are possible:
1) Write a regex with whitespace rules after each regular char. This will certainly blow up the regex pattern but is the most flexible one. For catching line breaks use DOT_ALL mode. DOT_ALL will however produce the same problems as the next approach.
2) (Temporarily) remove line breaks and use normal regex pattern matching. This approach has problems though as it can happen that you include more text than necessary (at the end of the URL) or don't find a URL (if the linebreak is at the start, messing up the protocol string).
2a) A modification of 2) could be to do several match attempts removing only certain line breaks, e.g. after looking for an initial URL part (e.g. www, http etc.). Only possible if recognition time is secondary.
3) Ease your task with domain specific knowlege. For instance if you know where line breaks can occur (or if they occur only at specific positions) then look for these specific cases and solve them first. Then return to the usual regex search.
3a) A variation of 3) could be to look specifically for the protocol and and page extension using a regex with full whitespace rules to find start and stop of an URL. This works obviously only if there's always a protocol/filename_with_extension. Transform the found tokens into regular ones without whitespaces (but include a space before the protocol and after the extension) and then remove all line breaks in the text. Now you can match the URL with a regular regex.
There are certainly more variations possible, but the general idea is the same.
I'm fairly new to figuring out how Regex works, but this one is just frustrating.
I have a massive XML document with a lot of <description>blahblahblah</description> tags. I want to basically remove any and all instances of <description></description>.
I'm using Eclipse and have tried a few examples of Regex I've found online, but nothing works.
<description>(.*?)</description>
Shouldn't that work?
EDIT:
Here is the actual code.
<description><![CDATA[<center><table><tr><th colspan='2' align='center'><em>Attributes</em></th></tr><tr bgcolor="#E3E3F3"><th>ID</th><td>308</td></tr></table></center>]]></description>
I'm not familiar with Eclipse, but I would expect its regex search facility to use Java's built-in regex flavor. You probably just need to check a box labeled "DOTALL" or "single-line" or something similar, or you can add the corresponding inline modifier to the regex:
(?s)<description>(.*?)</description>
That will allow the . to match newlines, which it doesn't by default.
EDIT: This is assuming there are newlines within the <description> element, which is the only reason I can think of why your regex wouldn't work. I'm also assuming you really are doing a regex search; is that automatic in Eclipse, or do you have to choose between regex and literal searching?
I keeping having the problem trying to extract data using regex whereas my result is not what I wanted because there might be some newlines, spaces, html tags, etc in the string, but is there anyway to actually see what is in the string, the debugger seems to show only the real text. How do you deal with this?
If the content of the string is HTML then debugger gives you a choice of viewing "HTML" or "Source". Source should show you any HTML tags that are there.
However if your concern is white space, this may not be enough. Your only option is to "view source" on the original page.
The best course of action is to explicitly handle these possibilities in your regex. For example, if you think you might be getting white space in your target string, use the \s* pattern in the critical positions. That will match zero or more spaces, tabs, and new lines (you must also have the "s" option checked in the regex panel for new lines).
However, without specific examples of source text and the regex you are using - advice can only be generic.
What I do is use a regex tester (whichever uses the same regex engine that you are using) and I test my pattern on it. I've tried using text editors that display invisible characters but to me they only add to the confusion.
So I just go by trial and error. For instance, if a line ends in:
</a>
Then I'll try the following patterns on the regex tester until I find one that works:
</a>.
</a>..
</a>\s
</a>\s*
</a>\n
</a>\r
</a>\r\n
Etc.