I currently have the following regex
".*[0-9].*"
The above makes sure that the text has a number in it. I would also like to add the condition of minimum length to it say 8 characters. How can I add another condition to the above expression making sure that there are at least 8 characters in the text ?
Solution
You can use Positive Lookaheads to validate a string before capturing it.
Regex
(?=^.{8,}$)(?=^.*\d)^.*$
Explanation
The syntax for a Positive Lookahead is like so: (?=REGEX)
In the regex above, I have specified ^.{8,}$ inside the first Lookahead. This means that the string MUST have a MINIMUM of 8 characters from start to finish in order to pass validation.
The second positive lookahead has ^.*\d. This means that the string can begin with any characters, but there must be a digit somewhere in the string, otherwise it will not pass validation.
The last bit is simply "match everything" ^.*$, because if it passed the initial validation, then we want to capture it.
Demonstration
Regex101 Example
The regex for checking minimum and maximum element goes as follow
{2} contains 2 element
{2,5} contains 2 to 5 element
{2,} contains 2 or more
You can also check this PDF file for more information
Good luck
Related
The first thing I tried to do, is get the regex matching what I DON'T want. This way, I could just flip it to NOT accept that same input. This is where I came up with the first part of this regex.
Accept all 9 digit numbers, where all 9 digits are identical (without dashes): "^(\d)\1{8}$". This expression works as expected (as seen here: (https://regex101.com/r/Ez8YC3/1)).
The second expression should do the same, with dashes formatted as follows xxx-xx-xxxx: "^(\d)\1{8}$". This expressions works as expected (as seen here: https://regex101.com/r/bodzIX/1).
Now what I want to do at this point, is combine them together to look for BOTH conditions. However when I do that it seems to break, and only match 9 digit numbers that are identical throughout WITH dashes: "^(\d)\1{2}-(\d)\1{1}-(\d)\1{3}$|^(\d)\1{8}$". This can be seen here: https://regex101.com/r/lPnksf/1.
I may be getting a little ahead of myself here, but in order to show my work as much as possible, I also tried flipping those regex separately, which also did not work as expected.
Condition #1 flipped: "^(?!(\d)\1{8})$". Can be seen here: https://regex101.com/r/ed51yk/1.
Condition #2 flipped: "^(?!(\d)\1{2}-(\d)\1{1}-(\d)\1{3})$". Can be seen here: https://regex101.com/r/UYfoMK/1.
I would expect the two expressions (when flipped) to match any 9 digit number (with or without dashes) where all numbers are not identical. How ever this does not happen at all.
This is the final regex that I came up with, which is clearly not doing what I would expect it to: "^(?!(\d)\1{2}-(\d)\1{1}-(\d)\1{3})$|^(?!(\d)\1{8})$". Can be seen here: https://regex101.com/r/9eHhF5/1
At the end of the day, I want to combine these 2 expressions, with this one (that already works as intended): "^(?!000|666|9\d\d)\d{3}-(?!00)\d\d-(?!0000)\d\d\d\d$". Can be seen here: https://regex101.com/r/AdRI8i/1.
I am still pretty new to regex, and really want to understand why I can't simply wrap the condition in (?!...) in order to match the opposite condition.
Thank you in advance
What you want to do is not flip, but reverse the regex logic.
Yes, to reverse the pattern logic, you should use a negative lookahead, but there are caveats.
First, the $ end of string anchor: if it was at the end of the "positive" regex, it must also be moved to the lookahead in the reverse pattern. So, your ^(?!(\d)\1{8})$ regex must be written as ^(?!(\d)\1{8}$). Same goes for your second regex.
Next, mind that each subsequent capturing group gets an incremented ID number, so you cannot keep the same backreferences when you "join" patterns with OR | operator. You must adjust these IDs to reflect their new values in the new regex.
So, you want to match a string that matches ^(?!000|666|9\d\d)\d{3}-(?!00)\d\d-(?!0000)\d\d\d\d$ first (let's note \d\d\d\d = \d{4}), then you can add restrictions with lookaheads:
(?!(\d)\1{8}$) - fails the match if, immediately from the current position, it matches identical 9 digits and then the string end comes
(?!(\d)\2\2-(\d)\2-(\d)\2{3}$) - (note the ID incrementing continuation) fails the match if, immediately from the current position, it matches identical to the first one 3 digits, -, identical 2 digits, -, identical 5 digits, and then the string end comes.
So, to follow your logic, you can use
^(?!(\d)\1{8}$)(?!(\d)\2\2-(\d)\2-(\d)\2{3}$)(?!000|666|9\d\d)\d{3}-(?!00)\d\d-(?!0000)\d{4}$
See the regex demo
As the lookaheads are non-consuming patterns, i.e. the regex index remains at the same position after matching their pattern sequences where it was before, the 3 lookaheads will all be tried at the start of the string (see the ^ anchor). If any of the three negative lookaheads at the start fails, the whole string match will be failed right away.
By this Regex you match what you dont want as social security number:
^(?:(\d)\1{8})|(?:(\d)\2{2}-\2{2}-\2{4})$
Demo
By this regex you match only what you want:
^(?!(?:(\d)\1{8})|(?:(\d)\2{2}-\2{2}-\2{4})).*$
Demo
How do i extract four numbers starting after the 8th number which is dynamic from the following strings using regex.
20190715171712904_10008_file_activate_10.20.30.4000233223456_name.unl
20190715141712904_10008_runco_activate_10.20.30.40_name.unl
From first string i want 1717
From second string i want 1417
I have tried to write regex queries in https://regex101.com/ i.e.
I have tried ^\d{8}([0-9]{4})$ but not working.
Drop the $. It forces the expression to look for the end of the string after your 4 digits, which it is not. The answer will be in the first subgroup capture. Note you can use \d for the second [0-9] as well.
If your language supports look-behinds, you can capture your digits as the main capture, instead of a subgroup:
(?<=^\d{8})\d{4}
This is really not a problem for a regular expression though - getting the substring indexed from index 4 to index 7 including (0 indexed) is basic and faster in any language.
I am trying to generate a regular expression that will match any numbers within the range of 99 and 9999999. I have trouble understanding how generating number ranges generally works. I managed to find a range generator online that does the job for me, but I want to understand how it actually works.
My attempt to do this range is as follows:
(99|[1-9][0-9][0-9]|[1-9][0-9][0-9][0-9])
This is supposed to match 99, any 3 digit number or any 4 digit number, but it does not work as expected. When tested it matches only numbers 99 and 3 digit numbers. Four digit numbers are not matched at all. If I only write the part for 4 digit numbers on its own as
[1-9][0-9][0-9][0-9]
It matches 4 digit numbers, but when I construct it as in the first example it does not work. Can someone give me some clarification how this actually works and how successfully to generate a regular expression for the range of 99 to 9999999.
Link to demo - Here
So you want to know how this works...
Regexs have no real understanding of the values of numbers in your string, it only cares how they are represented, which is why looking for numbers in a range seems more awkward than it should be. The only reason your regex engine can understand a range in a character class like [0-9] at all is because of the characters' positions in a list (a character range like [&-~] is just as valid, and equally understandable to it.)
So, to match a range like 99-9999999, ya gotta spell out what that looks like: literal "99", or three digits without a leading zero, or four digits without a leading zero, and so on.
But this is what your demo did, right? And it didn't work. Of your test string "9293" your regex only matched "929". What happened here is the regex engine is eager to return a complete match - as soon as it found one it returned it, even though a better/longer match might have occurred later.
Here's how that match happened. (I'll skip some details like grouping, as they're not super relevant here.)
Step 1.
The engine compares the first token in the regex with the first character in the string
(99|[1-9][0-9][0-9]|[1-9][0-9][0-9][0-9])
9293 ✅
Success, they match.
Step 2.
The engine then advances both to the next token in the regex and the next character in the string and compares them.
(99|[1-9][0-9][0-9]|[1-9][0-9][0-9][0-9])
9293 ❌
Failure, no match. The engine would stop and return the failure here, but you're using alternation via |, so it knows there's an alternate expression to try.
Step 3.
The engine advances to the first token of the next alternate expression in the regex, and rewinds the position in the string.
(99|[1-9][0-9][0-9]|[1-9][0-9][0-9][0-9])
9293 ✅
Success, they match.
Step 4.
Continuing on.
(99|[1-9][0-9][0-9]|[1-9][0-9][0-9][0-9])
9293 ✅
Match.
Step 5.
And again.
(99|[1-9][0-9][0-9]|[1-9][0-9][0-9][0-9])
9293 ✅
Success. The complete expression matches. There's no need to try the remaining alternate. The match here returned is:
929
As you've probably figured out, if your input string was instead "9923" then step 2 would've matched and the engine there would've stopped and returned "99".
As you've also probably figured out, if you rearrange your alternate expressions from longest to shortest
([1-9][0-9][0-9][0-9]|[1-9][0-9][0-9]|99)
the longest would be attempted first, which would match and return your expected "9293".
Simplifying
It's still pretty wordy though, especially as you crank up the number of digits in your range. There are a couple things you can do to simplify it.
The character class [0-9] can be represented by the shorthand character class \d.
([1-9]\d\d\d|[1-9]\d\d|99)
And instead of repeating them use a quantifier in curly brackets like so:
([1-9]\d{3}|[1-9]\d{2}|99)
As it happens, quantifiers can also take the form of {min, max}, so you can combine the two similar alternates:
([1-9]\d{2,3}|99)
You might expect this to land you back returning "929" again, the engine being eager and all, but quantifiers are by default greedy so they'll try to pick up as much as they can. This lends itself well to your larger desired range:
([1-9]\d{2,6}|99)
Finishing up
What you do with it from here depends on what you need the regex to do. As it stands the parentheses are superfluous, there's no point in creating a capturing group of the entire regex itself. However a decision comes when you've got an input string like:
You will likely be eaten by 1000 grue.
If you're trying to pluck out how many grue are about to eat you, you might use
[1-9]\d{2,6}|99
which will return 1000.
However that sorta runs back into the original problem with your demo. If it's "12345678 grue", which is out of range, this'll match "1234567" which might not be what you want. You can make sure the number you've matched isn't immediately followed by (or preceded by) another digit by using negative lookarounds.
(?<!\d)([1-9]\d{2,6}|99)(?!\d)
(?<!\d) means "from this position, the prior character is not a digit" while (?!\d) means "from this position, the next character is not a digit."
The parentheses around the alternates are back as they're necessary for grouping here, otherwise the lookbehind would only be part of and apply in the first alternate expression and the lookahead would only be part of and apply in the second alternate.
On the other hand if you're trying to make sure the entire string only consists of a number in your range you'll want to instead use the anchors ^ and $ (start of string and end of string, respectively):
^([1-9]\d{2,6}|99)$
And finally you can trade the capturing group out for a non-capturing group (?:...), so:
^(?:[1-9]\d{2,6}|99)$
or
(?<!\d)(?:[1-9]\d{2,6}|99)(?!\d)
You'll still grab the number as the match, it just won't be repeated in a group capture. (Lookarounds are already non-capturing, no need to worry about those.)
First of all you need some string boundaries for you regex (anything except digit, in my example I use ^ and $ -- begging and end of line or string)
Try this one:
^([1-9][0-9]{2,6}|99)$
I'm having a lot more difficulty than I anticipated in creating a simple regex to match any specific characters, including a range of characters from the alphabet.
I've been playing with regex101 for a while now, but every combination seems to result in no matches.
Example expression:
[\n\r\t\s\(\)-]
Preferred expression:
[[a-z][a-Z]\n\r\t\s\(\)-]
Example input:
(123) 241()-127()()() abc ((((((((
Ideally the expression will capture every character except the digits
I know I could always manually input "abcdefgh".... but there has to be an easier way. I also know there are easier ways to capture numbers only, but there are some special characters and letters which I may eventually need to include as well.
With regex you can set the regex expression to trigger on a range of characters like in your above example [a-z] that will capture any letter in the alphabet that is between a and z. To trigger on more than one character you can add a "+" to it or, if you want to limit the number of characters captured you can use {n} where n is the number of characters you want to capture. So, [a-z]+ is one or more and [a-z]{4} would match on the first four characters between a and z.
You can use partial intervals. For example, [a-j] will match all characters from a to j. So, [a-j]{2} for string a6b7cd will match only cd. Also you can use these intervals several times within same group like this: [a-j4-6]{4}. This regex will match ab44 but not ab47
Overlooked a pretty small character. The term I was looking for was "Alternative" apparently.
[\r\t\n]|[a-z] with the missing element being the | character. This will allow it to match anything from the first group, and then continue on to match the second group.
At least that's my conclusion when testing this specific example.
I've got this RegEx example: http://regexr.com?34hihsvn
I'm wondering if there's a more elegant way of writing it, or perhaps a more optimised way?
Here are the rules:
Digits and dashes only.
Must not contain more than 10 digits.
Must have two hyphens.
Must have at least one digit between each hyphen.
Last number must only be one digit.
I'm new to this so would appreciate any hints or tips.
In case the link expires, the text to search is
----------
22-22-1
22-22-22
333-333-1
333-4444-1
4444-4444-1
4444-55555-1
55555-4444-1
666666-7777777-1
88888888-88888888-1
1-1-1
88888888-88888888-22
22-333-
333-22
----------
My regex is: \b((\d{1,4}-\d{1,5})|(\d{1,5}-\d{1,4}))-\d{1}\b
I'm using this site for testing: http://gskinner.com/RegExr/
Thanks for any help,
Nick
Here is a regex I came up with:
(?=\b[\d-]{3,10}-\d\b)\b\d+-\d+-\d\b
This uses a look-ahead to validate the information before attempting the match. So it looks for between 3-10 characters in the class of [\d-] followed by a dash and a digit. And then after that you have the actual match to confirm that the format of your string is actually digit(dash)digit(dash)digit.
From your sample strings this regex matches:
22-22-1
333-333-1
333-4444-1
4444-4444-1
4444-55555-1
55555-4444-1
1-1-1
It also matches the following strings:
22-7777777-1
1-88888888-1
Your regexp only allows a first and second group of digits with a maximum length of 5. Therefore, valid strings like 1-12345678-1 or 123456-1-1 won't be matched.
This regexp works for the given requirements:
\b(?:\d\-\d{1,8}|\d{2}\-\d{1,7}|\d{3}\-\d{1,6}|\d{4}\-\d{1,5}|\d{5}\-\d{1,4}|\d{6}\-\d{1,3}|\d{7}\-\d{1,2}|\d{8}\-\d)\-\d\b
(RegExr)
You can use this with the m modifier (switch the multiline mode on):
^\d(?!.{12})\d*-\d+-\d$
or this one without the m modifier:
\b\d(?!.{12})\d*-\d+-\d\b
By design these two patterns match at least three digits separated by hyphens (so no need to put a {5,n} quantifier somewhere, it's useless).
Patterns are also build to fail faster:
I have chosen to start them with a digit \d, this way each beginning of a line or word-boundary not followed by a digit is immediately discarded. Other thing, using only one digit, I know the remaining string length.
Then I test the upper limit of the string length with a negative lookahead that test if there is one more character than the maximum length (if there are 12 characters at this position, there are 13 characters at least in the string). No need to use more descriptive that the dot meta-character here, the goal is to quickly test the length.
finally, I describe the end of string without doing something particular. That is probably the slower part of the pattern, but it doesn't matter since the overwhelming majority of unnecessary positions have already been discarded.