I'm trying to build a Regex expression for matching just snake case strings. I'm not really good at Regex. What I've built is:
([a-zA-Z]+)_([a-zA-Z]+)
But this isn't quite good because it doesn't match all the cases. I want to be able to add more words, not just 2, and also, I want to match just letters and the underscore. I mention that I'll use this with Javascript.
Do you have some better options, please? :) Thanks!
[a-zA-Z]+(_[a-zA-Z]+)*
should work fine
Version with non-capturing groups:
[a-zA-Z]+(?:_[a-zA-Z]+)*
Related
This question already has answers here:
Regular expression to stop at first match
(9 answers)
Closed 2 years ago.
I have this gigantic ugly string:
J0000000: Transaction A0001401 started on 8/22/2008 9:49:29 AM
J0000010: Project name: E:\foo.pf
J0000011: Job name: MBiek Direct Mail Test
J0000020: Document 1 - Completed successfully
I'm trying to extract pieces from it using regex. In this case, I want to grab everything after Project Name up to the part where it says J0000011: (the 11 is going to be a different number every time).
Here's the regex I've been playing with:
Project name:\s+(.*)\s+J[0-9]{7}:
The problem is that it doesn't stop until it hits the J0000020: at the end.
How do I make the regex stop at the first occurrence of J[0-9]{7}?
Make .* non-greedy by adding '?' after it:
Project name:\s+(.*?)\s+J[0-9]{7}:
Using non-greedy quantifiers here is probably the best solution, also because it is more efficient than the greedy alternative: Greedy matches generally go as far as they can (here, until the end of the text!) and then trace back character after character to try and match the part coming afterwards.
However, consider using a negative character class instead:
Project name:\s+(\S*)\s+J[0-9]{7}:
\S means “everything except a whitespace and this is exactly what you want.
Well, ".*" is a greedy selector. You make it non-greedy by using ".*?" When using the latter construct, the regex engine will, at every step it matches text into the "." attempt to match whatever make come after the ".*?". This means that if for instance nothing comes after the ".*?", then it matches nothing.
Here's what I used. s contains your original string. This code is .NET specific, but most flavors of regex will have something similar.
string m = Regex.Match(s, #"Project name: (?<name>.*?) J\d+").Groups["name"].Value;
I would also recommend you experiment with regular expressions using "Expresso" - it's a utility a great (and free) utility for regex editing and testing.
One of its upsides is that its UI exposes a lot of regex functionality that people unexprienced with regex might not be familiar with, in a way that it would be easy for them to learn these new concepts.
For example, when building your regex using the UI, and choosing "*", you have the ability to check the checkbox "As few as possible" and see the resulting regex, as well as test its behavior, even if you were unfamiliar with non-greedy expressions before.
Available for download at their site:
http://www.ultrapico.com/Expresso.htm
Express download:
http://www.ultrapico.com/ExpressoDownload.htm
(Project name:\s+[A-Z]:(?:\\w+)+.[a-zA-Z]+\s+J[0-9]{7})(?=:)
This will work for you.
Adding (?:\\w+)+.[a-zA-Z]+ will be more restrictive instead of .*
I was using a lookbehind to check for a dot before the # but just realized not all browsers are supporting lookbehinds. It works perfect in Chrome but fails in Firefox and IE.
This is what I came up with but it certainly is messy
^([a-zA-Z0-9&^*%#~{}=+?`_-]\.?)*[a-zA-Z0-9&^*%#~{}=+?`_-]#([a-zA-Z0-9]+\.)+[a-zA-Z]$
Is there a simpler and/or more elegant way to do this? I don't think I can negate the dot (^.) because I'm only allowing certain characters to be present in the local part.
This ([a-zA-Z0-9&^*%#~{}=+?`_-].?)*[a-zA-Z0-9&^*%#~{}=+?`_-] part is not messy, but inefficient, because the * quantifies a group containing an obligatory part, [...], and an optional \.?. Instead of (ab?)*a, you may use a+(?:ba+)* that will make matching linear and swift, in your case, [a-zA-Z0-9&^*%#~{}=+?`_-]+(?:.[a-zA-Z0-9&^*%#~{}=+?`_-]+)*.
More, [a-zA-Z0-9_] equals \w in JS regex, you may use this to shorten the pattern.
Besides, the last [a-zA-Z]$ pattern only matches a single letter, you most probably need [a-zA-Z]{2}$ there, as TLDs consist of 2+ letters.
So, you may use
^[\w&^*%#~{}=+?`-]+(?:\.[\w&^*%#~{}=+?`-]+)*#(?:[a-zA-Z0-9]+\.)+[a-zA-Z]{2,}$
See the regex demo.
I don't want to capture the first 150 characters and then capture everything else.
/(?<=\A.{150})(.*)/g
this is the expression I wrote in PHP but I need to do it in JavaScript and I cant work around not having lookbehind
this is javascript regex that I wrote
/(?:.*)(?!.{150})/g
You're overthinking it.
The pattern you want is /^.{150}(.*)/, and then you pull out the contents of capture group 1. And, for added fun, this pattern will work equally well in just about every engine under the sun, because it uses only basic token types and quantifiers.
Demo on Regex101
You don't need lookarounds for this
^.{150}(.+)
is all you need. https://regex101.com/r/P7keW9/1
This question already has answers here:
Regular expression to stop at first match
(9 answers)
Closed 2 years ago.
I have this gigantic ugly string:
J0000000: Transaction A0001401 started on 8/22/2008 9:49:29 AM
J0000010: Project name: E:\foo.pf
J0000011: Job name: MBiek Direct Mail Test
J0000020: Document 1 - Completed successfully
I'm trying to extract pieces from it using regex. In this case, I want to grab everything after Project Name up to the part where it says J0000011: (the 11 is going to be a different number every time).
Here's the regex I've been playing with:
Project name:\s+(.*)\s+J[0-9]{7}:
The problem is that it doesn't stop until it hits the J0000020: at the end.
How do I make the regex stop at the first occurrence of J[0-9]{7}?
Make .* non-greedy by adding '?' after it:
Project name:\s+(.*?)\s+J[0-9]{7}:
Using non-greedy quantifiers here is probably the best solution, also because it is more efficient than the greedy alternative: Greedy matches generally go as far as they can (here, until the end of the text!) and then trace back character after character to try and match the part coming afterwards.
However, consider using a negative character class instead:
Project name:\s+(\S*)\s+J[0-9]{7}:
\S means “everything except a whitespace and this is exactly what you want.
Well, ".*" is a greedy selector. You make it non-greedy by using ".*?" When using the latter construct, the regex engine will, at every step it matches text into the "." attempt to match whatever make come after the ".*?". This means that if for instance nothing comes after the ".*?", then it matches nothing.
Here's what I used. s contains your original string. This code is .NET specific, but most flavors of regex will have something similar.
string m = Regex.Match(s, #"Project name: (?<name>.*?) J\d+").Groups["name"].Value;
I would also recommend you experiment with regular expressions using "Expresso" - it's a utility a great (and free) utility for regex editing and testing.
One of its upsides is that its UI exposes a lot of regex functionality that people unexprienced with regex might not be familiar with, in a way that it would be easy for them to learn these new concepts.
For example, when building your regex using the UI, and choosing "*", you have the ability to check the checkbox "As few as possible" and see the resulting regex, as well as test its behavior, even if you were unfamiliar with non-greedy expressions before.
Available for download at their site:
http://www.ultrapico.com/Expresso.htm
Express download:
http://www.ultrapico.com/ExpressoDownload.htm
(Project name:\s+[A-Z]:(?:\\w+)+.[a-zA-Z]+\s+J[0-9]{7})(?=:)
This will work for you.
Adding (?:\\w+)+.[a-zA-Z]+ will be more restrictive instead of .*
I need some help with a JS Regex.
Here's the string I'm passing, I want to delete everything before 'Hanyuu-sama' with JS Replace.
Hanyuu","dj":{"id":18,"djname":"Hanyuu-sama
The first and second "Hanyuu" can change, the id number can change. This has already been cropped quite a bit with regular expressions.
Now I've tried a few and surprisingly it's failing when I do simple and complex regexes:
I've tried:
.*\"
And it does nothing, I've tried disgusting stuff in my desperation:
.*\","dj\":{\"id":.*,\"djname\":\"
And nada.
Here's a JS Fiddle and here's a http://regex101.com/r/tE2uY0/1 Regex JS matching platform.
Does anyone know why this isn't working?
I know this is likely bad practice, I'm just trying to learn Regexes.
Bonus points if anyone can refer me to a good source to learn Regular expressions. I'd love a solution but I'd like to learn how to do this myself in the future and why this one failed even more.
Your method call should look like this:
source = source.replace(/.*"/, "");
Regular expression in javascript are written between /.../ and not "/.../" like they are in many other languages.
If your string is always structured like that and it does not contain any more characters, your regex should do the trick. That's because the * quantifier acts greedy by default, thus always matching the last " in the string.