I have a special requirement, where i need the achieve the following
No Special Character is allowed except _ in between string.
string should not start or end with _, . and numeric value.
underscore should not be allowed before or after any numeric value.
I am able to achieve most of it, but my RegEx pattern is also allowing other special characters.
How can i modify the below RegEx pattern to not allow any special character apart from underscore that to in between strings.
^[^0-9._]*[a-zA-Z0-9_]*[^0-9._]$
What you might do is use negative lookaheads to assert your requirements:
^(?![0-9._])(?!.*[0-9._]$)(?!.*\d_)(?!.*_\d)[a-zA-Z0-9_]+$
Explanation
^ Assert the start of the string
(?![0-9._]) Negative lookahead to assert that the string does not start with [0-9._]
(?!.*[0-9._]$) Negative lookahead to assert that the string does not end with [0-9._]
(?!.*\d_) Negative lookahead to assert that the string does not contain a digit followed by an underscore
(?!.*_\d) Negative lookahead to assert that the string does not contain an underscore followed by a digit
[a-zA-Z0-9_]+ Match what is specified in the character class one or more times. You can add to the character class what you would allow to match, for example also add a .
$ Assert the end of the string
Regex demo
Keep it simple. Only allow underscore and alphanumeric regex:
/^[a-zA-Z0-9_]+$/
Javascript es6 implementation (works for React):
const re = /^[a-zA-Z0-9_]+$/;
re.test(variable_to_test);
Your opening and closing sections; [^0-9._], say match ANY character other than those.
So you need to change it to be what you can match.
/^[A-Z][A-Z0-9_]*[A-Z]$/i
And since you now said one character is valid:
/^[A-Z]([A-Z0-9_]*[A-Z])?$/i
Related
I need a regex that disallows double underscore in the word, but with a one exemption: if it is at the end and followed by x - then string is valid. Symbols order doesn't play role.
For example:
Foo_bar__x = VALID
Foo__bar_x = INVALID
A string can contain more than one single underscore, and alphanumeric symbols. Here is regex that almost suits my requirements , it makes "__" forbidden, but it doesn't handle the case with __x ending:
^(?!.*__.*)\w+$
You may use this regex with negative lookahead:
/^(?!.*__(?!x$))\w+$/
RegEx Demo
(?!.*__(?!x)) is a negative lookahead that asserts failure when we get __ that is followed by any character other than x at the end of input.
Nested negative lookahead (?!x$) is for asserting double underscores are not followed by x before end to get a successful match.
I have this ^[a-zA-Z0-9 #&$]*$, but not working for me in few cases.
If someone types
A string that only consists of digits (e.g. 1234567)
A string starting with a special character (e.g. &123abc)
need to be rejected. Note that a special char can be in the middle and at the end.
You seem to need to avoid matching strings that only consist of digits and make sure the strings start with an alphanumeric. I assume you also need to be able to match empty strings (the original regex matches empty strings).
That is why I suggest
^(?!\d+$)(?:[a-zA-Z0-9][a-zA-Z0-9 #&$]*)?$
See the regex demo
Details
^ - start of string
(?!\d+$) - the negative lookahead that fails the match if a string is numeric only
(?:[a-zA-Z0-9][a-zA-Z0-9 #&$]*)? - an optional sequence of:
[a-zA-Z0-9] - a digit or a letter
[a-zA-Z0-9 #&$]* - 0+ digits, letters, spaces, #, & or $ chars
$ - end of string.
you can do it with the following regex
^(?!\d+$)\w+\S+
check the demo here
I have this regex
/^[a-z]{1,}( (?=[a-z])){0,}(_(?=[a-z])){0,}[a-z]{0,}$/
I want to match
ag_b_cf_ajk
or
zva b c de
or
hh_b opxop a_b
so any character tokens separated by a single space or underscore.
(In the regex above, we have a literal space, which is legal, and we have look-aheads that ensure that a space or underscore is followed by a character).
The problem is, my above regex is only matching the first space or underscore, like so:
axz_be
axz be
but these fail
axz_be_j
axz be j
I believe I missing some concept with regexes in order to solve this as I have been trying for the last few hours!
It seems you can just use
^[a-z]+(?:[_ ][a-z]+)*$
See the regex demo
The regex matches
^ - start of string
[a-z]+ - one or more lowercase ASCII letters
(?:[_ ][a-z]+)* - zero or more sequences of:
[_ ] - a space or an underscore
[a-z]+ - one or more lowercase ASCII letters
$ - end of string
If the space or underscore must appear at least once, use the + quantifier instead of *:
^[a-z]+(?:[_ ][a-z]+)+$
^
To add a multicharacter alternative to the underscore and hyphen, you need to introduce another non-capturing group:
^[a-z]+(?:(?:[_ ]|\[])[a-z]+)+$
See another regex demo
I am trying to make regexp for validating string not containing
^ ; , & . < > | and having 1-20 characters. Any other Unicode characters are valid (asian letters for example).
How to do it?
You can use the following:
^[^^;,&.<>|]{1,20}$
Explanation:
^ assert starting of the string
[^ start of negated character class ([^ ])
^;,&.<>| all the characters you dont want to match
] close the negates character class
{1,20} range of matches
$ assert ending of the string
It will match any character other than specified characters within range of 1-20.
Your regex \w[^;,&.<>|]{1,20} contains \w that might not match all Unicode letters (I guess your regex flavor does not match Unicode letters with \w). Anyway, the \w only matches 1 character in your pattern.
Also, you say you need to exclude ^ but it is missing in your pattern.
When you want to validate length, you also must use ^/$ anchors to mark the beginning and end of a string.
To create a pattern for some range that does not match specific characters, you need a negated character class with anchors around it, and the length is set with limiting quantifiers:
^[^^;,&.<>|]{1,20}$
Or (this version makes sure we only match at the beginning and end of the string, never a line):
\A[^^;,&.<>|]{1,20}\z
Note that inside a character class, almost all special characters do not require escaping (only some of them, none in your case). Even the ^ caret symbol.
See demo
I would like to have a regex which matches the string with NO whitespace(s) at the beginning. But the string containing whitespace(s) in the middle CAN match. So far i have tried below
[^-\s][a-zA-Z0-9-_\\s]+$
Debuggex Demo
Above is not allowing whitespace(s) at the beginning, but also not allowing in the middle/end of the string. Please help me.
In your 2nd character class, \\s will match \ and s, and not \s. Thus it doesn't matches a whitespace. You should use just \s there. Also, move the hyphen towards the end, else it will create unintentional range in character class:
^[^-\s][a-zA-Z0-9_\s-]+$
If you plan to match a string of any length (even an empty string) that matches your pattern and does not start with a whitespace, use (?!\s) right after ^:
/^(?!\s)[a-zA-Z0-9_\s-]*$/
^^^^^^
Or, bearing in mind that [A-Za-z0-9_] in JS regex is equal to \w:
/^(?!\s)[\w\s-]*$/
The (?!\s) is a negative lookahead that matches a location in string that is not immediately followed with a whitespace (matched with the \s pattern).
If you want to add more "forbidden" chars at the string start (it looks like you also disallow -) keep using the [\s-] character class in the lookahead:
/^(?![\s-])[\w\s-]*$/
To match at least 1 character, replace * with +:
/^(?![\s-])[\w\s-]+$/
See the regex demo. JS demo:
console.log(/^(?![\s-])[\w\s-]+$/.test("abc def 123 ___ -loc- "));
console.log(/^(?![\s-])[\w\s-]+$/.test(" abc def 123 ___ -loc- "));
You need to use this regex:
^[^-\s][\w\s-]+$
Use start anchor ^
No need to double escape \s
Also important is to use hyphen as the first OR last character in the character class.
\w is same as [a-zA-Z0-9_]
use \S at the beginning
^\S+[a-zA-Z0-9-_\\s]+$
This RegEx will allow neither white-space at the beginning nor at the end of. Your string/word and allows all the special characters.
^[^\s].+[^\s]$
This Regex also works Fine
^[^\s]+(\s+[^\s]+)*$
try this should work
[a-zA-Z0-9_]+.*$
/^[^.\s]/
try this instead it will not allow a user to enter character at first place
^ matches position just before the first character of the string
. matches a single character. Does not matter what character it is, except newline
\s is space
If your field for user name only accept letters and middle of space but not for begining and end
User name: /^[^\s][a-zA-Z\s]+[^\s]$/
If your field for user ID only accept letters,numbers and underscore and no spaces allow
user ID: /^[\w]+$/
If your field for password only accept letters,number and special character no spaces allow
Password: /^[\w##&]+$/
Note: \w content a-zA-Z, number, underscore (_) if you add more character, add you special character after \w.
You can compare with user ID and password field in password field im only add some special character (##&).
India public thoko like 😁
I suggest below regex for this,
^[^\s].*[^\s]$
You can try regex in here