Using regex I'm trying to remove empty bbcode tags. By empty I mean nothing in between them:
[tag][/tag]
If there is something between them then it should be kept.
I've searched a lot and played around with a regex tester but haven't come up with anything that works right.
Edit: I realize now why I was having a hard time with this. In addition to the example above, I also have one's like:
[url=http://www.somedomain.com/][/url]
I'm trying to cleanup bbcode when a form is submitted so it's not stored since it's unneeded.
In Javascript, you could do :
str.replace(/\[([^\[\]]*)\]\[\/\1\]/g, '');
The operative aspect of regex in this case is the use of internal backrefs; I'm not sure, off the top of my head, whether this is universally supported, but .NET, in any case, seems to use PCRE (is this true?).
The pattern, then, is [, a word, ][/, the same word, ]. If we assume the word has simply the quality of "does not contain ]", then an appropriate regex to match an empty tag is \[([^\]]+)\]\[/\1\], escaped as necessary in context.
For the second case, if assume the form [tag=arg][/tag], and that tag and arg each don't contain any ']' (not a reasonable assumption! but dealing with it is left as an exercise for the reader -- and I'm quite sure most bbcode implementations don't actually deal with that problem, either), one could use a regex \[([^\]=]+)(=[^\]]*)?\]\[/\1\].
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 need to select src=" using a regular expression in the form: //, but only if it is within an image tag.
This should return true:
<img alt="Alt text" src="/directory/Images/my-image.jpg" />
This to return false:
<script type="text/javascript" async="" src="https://www.google-analytics.com/analytics.js"></script>
The end result will be replacing the scr=", which the application I am using performs, I need the regex for the find.
First, the standard disclaimer: if you are using regexes to parse a HTML DOM, you are DOING IT WRONG. With all structured data (XML, JSON, and so forth), the right way to parse HTML is to use something built for that purpose, and query it using its querying system.
That said, it is often the case that what you want is a quick hack on the commandline or the search field of an editor or whatever, and you don't want or need to faff with writing an application that loads in DOM-parsing libraries.
In that case, if you're not actually writing a program, and you don't mind that there are edge-cases where any regex you try will break, then consider something like this:
/<img\b[^<>]+\bsrc\s*=\s*"([^"]+)"/i ... maybe replacing the leading / and trailing /i with whatever other thing your language uses to denote a case-insensitive regular expression.
Note that this makes assumptions, that the url is quoted with doublequotes, the tag is correctly formed, there are no extraneous <img strings in the document, there are no doublequotes in the URL, and countless others that I didn't think of, but a proper parser would. These assumptions are a large part of why using a parser is so important: it makes no such assumptions, and if fed garbage, will correctly let you know that you did so, rather than trying to digest it and giving you pain later on.
<img\b - an img tag. The word boundary ensures this isn't an imgur tag or whatever.
[^<>]+ - one or more characters, with no closing tag, and for safety, no opening tags either.
\bsrc\s*=\s* - 'src=', but with optional whitespace, and another word-boundary check.
"([^"]+)" - some URL consisting of non-quote characters, within quotes.
Now, be aware that since we're doing NO security checking on the URL, you could be grabbing anything, such as javascript:...something malicious..., or it could be 6GB long - you just don't know. You could add in checking for such things, but you'll always miss something, unless you control the input and know exactly what you're parsing.
Your mention of "my application" does mean that I must reiterate: the above is almost certainly the wrong way to do it if you are writing an application, and the question you should be asking is probably closer to "how do I get the value of the src attribute of an img tag from a HTML page, in my chosen programming language?" rather than "how do I use regexes to extract this token from this HTML tag?"
When I say this, I don't mean "ivory-tower computer scientists will look down their nose at you" - though I admit there can be a lot of that kind of snootiness in programming :D
I mean something more like... "you're setting yourself up for pain as you run into edge-case after edge-case, and spiral down into a deep rabbit-hole of infinitely refining your regex. And you can likely avoid the pain with a simple one-liner, infinitely nicer than regex, perhaps document.querySelector('img[src^="/directory/Images"]') as #LGSon suggests in a comment.
People will say this because they've had this pain, and they're wincing at the idea that you might suffer it too.
There are several ways to match that. This RegEx is just an example and it is not certainly the best expression:
(src=")(.+)(.jpg|.JPG|.PNG|.png|.JPEG)"
You can wrap your target image URLs with a capturing group (), maybe similar to this expression:
(src=")((.+)(.jpg|.JPG|.PNG|.png|.JPEG))"
and simply call it using $2 (group #2).
You can also simplify it as you wish by adding ignore flag such as this expression:
src="((.+)(\.[a-rt-z]+))"
This is my reg expression that find it
(<instance_material symbol="material_)([0-9]+)(part)(.*?)(")(/)(>)
I need to find a string that does not contain the word "part"
and the xml lines are
<instance_material symbol="material_677part01_h502_w5" target="#material_677part01_h502_w5"/>
<instance_material symbol="material_677" target="#material_677"/>
You can use negative lookahead
^(?!.*part).*?$
^ - start of string.
(?!.*part) - condition to avoid part.
.*? - Match anything except new line.
$ - End of string
Demo
Many regex starters will encounter the problem finding a string not containing certain words. You could find more useful tips on Regular-Expression.info.
^((?!part).)*$
You need to be aware that all attempts to process XML using regular expressions are wrong, in the sense that (a) there will be some legitimate ways of writing the XML document that the regex doesn't match, and (b) there will be some ways of getting false matches, e.g. by putting nasty stuff in XML comments. Sometimes being right 99% of the time is OK of course, but don't do this in production because soon we'll have people writing on SO "I need to generate XML with the attributes in a particular order because that's what the receiving application requires."
Your regex, for example, requires the attribute to be in double rather than single quotes, and it doesn't allow whitespace around the "=" sign, or in several other places where XML allows whitespace. If there's any risk of people deliberately trying to defeat your regex, you need to consider tricks like people writing p in place of p.
Even if this is a one-off with no risk of malicious subversion, you're much better off doing this with XPath. It then becomes a simple query like //instance_materal[#symbol[not(contains(., 'part'))]]
Let's take an url like
www.url.com/some_thing/random_numbers_letters_everything_possible/set_of_random_characters_everything_possible.randomextension
If I want to capture "set_of_random_characters_everything_possible.randomextension" will [^/\n]+$work? (solution taken from Trying to get the last part of a URL with Regex)
My question is: what does the "\n" part mean (it works even without it)? And, is it secure if the url has the most casual combination of characters apart "/"?
First, please note that www.url.com/some_thing/random_numbers_letters_everything_possible/set_of_random_characters_everything_possible.randomextension is not a URL without a scheme like http:// in front of it.
Second, don't parse URLs yourself. What language are you using? You probably don't want to use a regex, but rather an existing module that has already been written, tested, and debugged.
If you're using PHP, you want the parse_url function.
If you're using Perl, you want the URI module.
Have a look at this explanation: http://regex101.com/r/jG2jN7
Basically what is going on here is "match any character besides slash and new line, infinite to 1 times". People insert \r\n into negated char classes because in some programs a negated character class will match anything besides what has been inserted into it. So [^/] would in that case match new lines.
For example, if there was a line break in your text, you would not get the data after the linebreak.
This is however not true in your case. You need to use the s-flag (PCRE_DOTALL) for this behavior.
TL;DR: You can leave it or remove it, it wont matter.
Ask away if anything is unclear or I've explained it a little sloppy.
I'm being lazy tonight and don't want to figure this one out. I need a regex to match 'jeremy.miller' and 'scottgu' from the following inputs:
http://codebetter.com/blogs/jeremy.miller/archive/2009/08/26/talking-about-storyteller-and-executable-requirements-on-elegant-code.aspx
http://weblogs.asp.net/scottgu/archive/2009/08/25/clean-web-config-files-vs-2010-and-net-4-0-series.aspx
Ideas?
Edit
Chris Lutz did a great job of meeting the requirements above. What if these were the inputs so you couldn't use 'archive' in the regex?
http://codebetter.com/blogs/jeremy.miller/
http://weblogs.asp.net/scottgu/
Would this be what you're looking for?
'/([^/]+)/archive/'
Captures the piece before "archive" in both cases. Depending on regex flavor you'll need to escape the /s for it to work. As an alternative, if you don't want to match the archive part, you could use a lookahead, but I don't like lookaheads, and it's easier to match a lot and just capture the parts you need (in my opinion), so if you prefer to use a lookahead to verify that the next part is archive, you can write one yourself.
EDIT: As you update your question, my idea of what you want is becoming fuzzier. If you want a new regex to match the second cases, you can just pluck the appropriate part off the end, with the same / conditions as before:
'/([^/]+)/$'
If you specifically want either the text jeremy.miller or scottgu, regardless of where they occur in a URL, but only as "words" in the URL (i.e. not scottgu2), try this, once again with the / caveat:
'/(jeremy\.miller|scottgu)/'
As yet a third alternative, if you want the field after the domain name, unless that field is "blogs", it's going to get hairy, especially with the / caveat:
'http://[^/]+/(?:blogs/)?([^/]+)/'
This will match the domain name, an optional blogs field, and then the desired field. The (?:) syntax is a non-capturing group, which means it's just like regular parenthesis, but won't capture the value, so the only value captured is the value you want. (?:) has a risk of varying depending on your particular regex flavor. I don't know what language you're asking for, but I predominantly use Perl, so this regex should pretty much do it if you're using PCRE. If you're using something different, look into non-capturing groups.
Wow. That's a lot of talking about regexes. I need to shut up and post already.
Try this one:
/\/([\w\.]+)\/archive/