Is there an easy way to get the opposite of a regex or do I need to build a new regex that produces the opposite of what I have?
For example, I use this regex to make sure I'm getting proper currency values -- without $ sign.
/^[0-9]+(\.[0-9][0-9]?)?$/
I want to now remove everything that falls outside this pattern. For example, if user enters letters or tries to enter two periods e.g. 7.50.6, I want to remove undesired characters. How do I do that?
I think you're going at this in the wrong way. First of all, trying to hide input error in such a way is a bad idea. If a user has to type a number and they put an extra dot, what tells you which is the good part and which is the bad? You're better off telling the user there's something wrong with their input.
But typically, you use a regex by specifying what it has to look like AND what are the significant portions you want to keep using capture groups.
This is a capture group: ([a-z0-9])#example.com; this is a non-capture group: (?:hello|hi).
In case of a phone number, all that matters are the digits, so you can capture them and accept multiple forms of in-between characters. Here's a simple one for a postal code:
([A-Z][0-9][A-Z]) ?([0-9][A-Z][0-9])
Then all you have to do is combine the captured groups. If present, the space won't be captured.
Find more examples on MDN.
Related
Background
I'm working on a Javascript application where users have to use a specific email domain to sign up (Either #a.com or #b.com. Anything else gets rejected).
I've created a regex string that makes sure the user doesn't do #a.com with nothing in front of it and limits users to only #a.com and #b.com. The last step is to make sure the user doesn't add extra characters to the end of #a.com by doing something like #a.com.gmail.com
This is the regex I currently have:
\b[a-zA-Z0-9\.]*#(a.com|b.com)
Question
What can I use at the end to prevent anything from being added after a.com or b.com? I'm very novice at regex and have no idea where to start.
To solve your problem add $ to the regex's end. $ means your match should be at the strings' end.
Also you can reduce (a.com|b.com) to [ab]\.com. Look I've also escaped the dot
The character class [ab] means one of its characters should be matched.
Check this demo.
As stated in the comments, be sure to use the (m)ultiline flag, this way the regex engine will threat each line as a separate string.
I am building a RegEx that is almost complete, but I can not get it to check for digits (0 - 9):
So for example: Jones-Parry is valid but Jones-Parry1 is not. The regex at present looks like this:
^([\\w\\s,'\\-ÀÈÌÒÙàèìòùÁÉÍÓÚÝáéíóúýÂÊÎÔÛâêîôûÃÑÕãñõÄËÏÖÜŸäëïöüŸçÇŒœßØøÅåÆæÞþÐð]){0,80}$
I have tried using \d and [0-9] but to no avail. All else is working with the regex aside from the numbers. It validates special characters etc.
Any pointers greatly appreciated!
The problem is \w expands to A-Za-z0-9_, which includes digits 0-9. This explains why strings with digit pass your test.
You may want to specify A-Za-z_ directly instead of \w in your regex. It will fix your problem.
As georg has pointed out in the comment, your regex is very weak, since aside from the length requirement, it only checks whether it does not contain any character outside your allowed character set. A string with only spaces, or a string with only punctuation would pass the test.
Anyway, I doubt validating name is a good idea in general. Many assumptions programmers make about name are wrong. Depending on your requirement, you can give user a field for display name, where user can type anything in, and another field for username, where you only allow a strict set of characters.
I have a form and I need to require letters and numbers. All the solutions I have seen, simply allow only letters and numbers but do not require both.
I have this Regex: /^[0-9a-zA-Z]+$/ which allows one or the other. How can I make this a requirement, meaning the text must contain at least a number.
Thanks my friends.
Guy
To break this down, we're requiring at least 2 characters, a letter and a number. In the code we start with the possibility of an alpha-numeric character. I'm not using \w because it also allows _ characters. In the group we have an or that looks for either a letter before a number, or a number before a letter. Then after the group we're requiring if anything exists that it also be alpha-numeric.
/^[A-Za-z0-9]*([A-Za-z][0-9]|[0-9][A-Za-z])[A-Za-z0-9]*$/i
As a recommendation, it's always best to use a server-side language as your front-line defense when validating a form instead of a Javascript-only approach. The reasons:
Someone can disable Javascript
The server needs to be protected from malicious attack (SQL or XSS injection)
Someone can bypass your form altogether by directly linking to the handler (if you're not requiring a valid referrer)
Some browsers like Lynx do not use Javascript, so it's not user friendly for people who need to use screen reading devices
I can't seem to wrap my head around this one and thought I'd ask for some help here!
Basically I am validating a password field and the requirements are as follows:
- Must contain 3 consecutive letters
- Must contain at least 2 digits
- Can be in any order (e.g. 1abc342, abc24g3, 11abcsjf)
Here is what I have so far but I believe it needs some tweaking:
/[a-z]{3}[0-9][0-9]/i
The regex you are describing can be written like so:
/(?=.*?[a-z]{3})(?=.*?\d.*?\d)/
The first lookahead searches for three letters in a row, in any position. The second lookahead looks for a digit in any position, followed by a digit further ahead.
You should probably do this in two separate regular expressions: one to test for three consecutive letters and one to test for at least two digits:
/[a-z]{3}/i
/\d.*d/
Make sure both conditions are met. You could use lookahead to combine this into one regex, but I think two regexes is clearer code and a better solution.
But if I may inject some opinion on the matter: Unless you have no control over this (client specified this), I'd highly recommend not imposing password restrictions like this. They actually make your password system far less secure, not more secure. Some reading on why:
http://jimpravetz.com/blog/2011/06/cheap-gpus-are-rendering-strong-passwords-use/
http://jimpravetz.com/blog/2012/02/stupid-password-rules/
In my web application, I create some framework that use to bind model data to control on page. Each model property has some rule like string length, not null and regular expression. Before submit page, framework validate any binded control with defined rules.
So, I want to detect what character that is allowed in each regular expression rule like the following example.
"^[0-9]+$" allow only digit characters like 1, 2, 3.
"^[a-zA-Z_][a-zA-Z_\-0-9]+$" allow only a-z, - and _ characters
However, this function should not care about grouping, positioning of allowed character. It just tells about possible characters only.
Do you have any idea for creating this function?
PS. I know it easy to create specified function like numeric only for allowing only digit characters. But I need share/reuse same piece of code both data tier(contains all model validator) and UI tier without modify anything.
Thanks
You can't solve this for the general case. Regexps don't generally ‘fail’ at a particular character, they just get to a point where they can't match any more, and have to backtrack to try another method of matching.
One could make a regex implementation that remembered which was the farthest it managed to match before backtracking, but most implementations don't do that, including JavaScript's.
A possible way forward would be to match first against ^pattern$, and if that failed match against ^pattern without the end-anchor. This would be more likely to give you some sort of match of the left hand part of the string, so you could count how many characters were in the match, and say the following character was ‘invalid’. For more complicated regexps this would be misleading, but it would certainly work for the simple cases like [a-zA-Z0-9_]+.
I must admit that I'm struggling to parse your question.
If you are looking for a regular expression that will match only if a string consists entirely of a certain collection of characters, regardless of their order, then your examples of character classes were quite close already.
For instance, ^[A-Za-z0-9]+$ will only allow strings that consist of letters A through Z (upper and lower case) and numbers, in any order, and of any length.