been doing Go programming on Codewars as a hobby and stumbled upon following task:
The code provided is supposed to replace all the dots . in the specified String with dashes -
But it's not working properly.
Task: Fix the bug so we can all go home early.
Initial wrong code:
regexp.MustCompile(`.`).ReplaceAllString(str, "-")
Through brute force, i've made it work like this:
regexp.MustCompile(`[.]`).ReplaceAllString(str, "-")
The correct answer is apparently this:
regexp.MustCompile(`\.`).ReplaceAllString(str, "-")
Could someone please explain the logic behind my solution and the right one.
Thank you in advance!
Your solution is correct too.
In regex, the dot define a special metacharacter but inside a character class it's a regular dot.
It is possible however to complain about the misleading impression of metacharacter use, so the escaped dot is more clear and easy to understand.
Related
I run a small forum that has an issue with people using parentheses to bracket statements. They do it to signify they are talking about Jews. I guess it is called echoes or something. So they will put a name like (((Prominent Person))) like that in the middle of a conversation.
I have recently been trying to combat this without just banning people that can't behave. I have a decent word filter but it doesn't block that. I recently installed something that allows me to use regex to strip things out but I am having trouble finding the proper string that doesn't break everything else.
"/\W{3}(.*)\W{3}/","$1"
The first is the matching string and the comma separates what is left. This string works, it strips the parentheses out and leaves everything else alone. The problem is that the string is too broad. It also strips out any [ brackets as well which breaks all of the bbcode in a post. Any post that has any number of at least 3 brackets will be broken after that.
I have been playing with different strings on regex101 but not finding the best solution. I need any time that ((( or ))) is seen to strip out those and replace it with nothing, like it never happened. It has to be exactly three and only ((( and not the other brackets it could trigger on.
Does anyone have a good solution?
\({3}(.*)\){3}
https://regex101.com/r/wD5TMb/1
So in your format probably: "/\({3}(.*)\){3}/","$1"
I have wrote some regex to match the first number in a number of project
^[^£]*£(?:[0-9\.,]+)[^£]*£([0-9\.,]+)
The problem which I am having is that it is not match all occurrences for the first number when they are being parsed below
RRP �50.00 - Now �39.99 // Not working
RRP �45 - Now �38 //Working
I was just wondering what is wrong because I cannot work it out. Thanks for any advice which you can give
Instead of directly specifying a character that might have issue(s) in regex engine to evaluate you may also try using it equivalent code:
^[^\u00A3]*\u00A3(?:[0-9\.,]+)[^\u00A3]*\u00A3([0-9\.,]+)
Not sure it solves your problem, but give it a try.
I would like to know if anybody can help me with a regular expression problem. I want to write a regular expression to catch URLs similar to this URL:
www.justin.tv/channel_name_here
I have tried:
/justin\.tv\/(.*)
The problem I get is that when this channel goes live, sometimes the URL transforms to something like this:
www.justin.tv/channel_name_here#/w/45365675688
I can't catch this. :( Can anybody please help me with this? I just want to catch the channel name without the pound symbol and the rest of the URL.
Here are some example URLs:
www.justin.tv/winning_movies#/w/6347562128
http://www.justin.tv/cine_accion_hd16#/w/6347562128/18
http://www.justin.tv/fox_movies_hd1/
I would want to get:
winning_movies
cine_accion_hd16
fox_movies_hd1
Thanks in advance! :)
Short answer:
(?<=justin\.tv\/)([^#\/]+)
Long answer:
Let's split this up into parts. Look at the back part first.
([^#\/]+)
This delimits the string into parts that don't include either '#' or '/'.
Now let's look at the first part.
(?<=justin\.tv\/)
The syntax "(?<=" followed by ")" is called positive lookbehind (this page has good examples and explanation of the different types of lookaround). Using a simple example:
(?<=A)B
The above example says "I want all 'B' that are immediately after an 'A'." Going to our big example, we're saying we want all parts (separated by '#' or '/') that are immediately after a part called "justin.tv/".
Look here for an example of the expression in action.
#justin\.tv/([^#/]+)#
If you want everything up to a certain character(-set), use a negated class.
Also, when working on regex for urls, using / as delimiter is error-prone, as you have to escape all the /'s. Use something else instead (like # in this case)
I have written this regex that works, but honestly, it’s like 75% guesswork.
The goal is this: I have lots of imports in Xcode, like so:
#import <UIKit/UIKit.h>
#import "NSString+MultilineFontSize.h"
and I only want to return the categories that contain +. There are also lots of lines of code throughout the source which include + in other contexts.
Right now, this returns all of the proper lines throughout the Xcode project. But if there is one thing I’ve learned from googling and searching Stack Overflow for regex tutorials, it is that there are LOTS of different ways to do things. I’d love to see all of the different ways you guys can come up with that make it either more efficient or more bulletproof regarding potential spoofs or misses.
^\#import+.[\"]*+.(?:(?!\+).)*+.*[\"]
Thanks in advance for all of your help.
Update
Also I suppose I’ll accept the answer of whoever does this with the shortest string, without missing any possible spoofs. But again, thanks to everyone who participates in this learning experience.
Resources from answers
This is an awesome resource for practicing regex from Dan Rasmussen: RegExr
The first thing I notice is that your + characters are misplaced: t+. matches t one or more times, followed by a single character .. I'm assuming you wanted to match the end of import, followed by one or more of any character: import.+
Secondly, # doesn't need to be escaped.
Here's what I came up with: ^#import\s+(.*\+.*)$
\s+ matches one or more whitespace character, so you're guaranteed that the line actually starts with #import and not #importbutnotreally or anything else.
I'm not familiar with xcode syntax, but the following part of the expression, (.*\+.*), simply matches any string with a + character somewhere in it. This means invalid imports may be matched, but I'm working under the assumption your trying to match valid code. If not, this will need to be modified to validate the importer syntax as well.
P.S. To test your expression, try RegExr. You can hover over characters to check what they do.
sed 's:^#import \(.*[+].*\):\1:' FILE
will display
"NSString+MultilineFontSize.h"
for your sample.
Hey everyone, I'm trying to type a regular expression that follows the following format:
someone#somewhere.com or some.one#some.where.com
There are no special characters or numbers permitted for this criteria. I thought I had it down, but I'm a bit rusty with regular expressions and when I tested mine, it failed all across the boards. So far, my regular is expression is:
^[a-zA-Z]+/.?[a-zA-Z]*#[a-zA-Z]+/.?[a-zA-Z]*/.com$
If anyone could help me, it would greatly be appreciated, thanks.
your regex looks good. I think you need to change the / to \ in front of the . .
Additionally, if you don't want someone.#somewhere..com pass your regex, u should change your regex to
^[a-zA-Z]+(\.[a-zA-Z]+)?#[a-zA-Z]+(\.[a-zA-Z]+)?\.com$
(not completely sure about the brackets () though, but i think that should be working)
its a backslash to espace dots. Also put the the parenthesis around the . and what follows otherwise an email like abc.#cde..com would be valid.
^[a-zA-Z]+(\.[a-zA-Z]+)?#[a-zA-Z]+(\.[a-zA-Z]+)?\.com$
It looks mostly OK. Change your / to \ though...
For the second case, I would ensure that if you have a . in the middle, it must be followed by more letters:
^[a-zA-Z]+(\.[a-zA-Z]+)?#[a-zA-Z]+(\.[a-zA-Z]+)?\.com$