Regular Expression - Avoid a string in expression

Question

I am trying to create a regex that should match following cases. if exact match of words 'first, second, third' then match should fail - but if there are any characters around it, then the string should be matched.

Also I need to avoid certain set of characters in the string. [()!=<>", ] - if these characters are part of string then match result should fail.

I looked at few examples & negative look ahead but did not get the right regex yet.

^(?!first$|second$|third$|fou rth$)[^()!=<>", ]+

desired output:

first - fail
second - fail
1first - pass
first1 - pass
1first1 - pass
fou rth - fail - it has space in between word and is from ignore list
newTest - pass
new(test - fail - since ( is not allowed character
space word - fail - since space is non allowed character

The regex needs to support case insensitive words

Any help appreciated. I am using javascript.

Gurmanjot Singh · Accepted Answer · 2017-11-11 11:02:56Z

3

Try this Regex:

^(?!.*[()!=<>", ])(?!(?:first|second|third)$).+$

Click for Demo

Explanation:

^ - asserts the start of the string
(?!.*[()!=<>", ]) - negative lookahead to validate that the test string does not contain any of these characters - (, ), !, =, <, >, ,,
(?!(?:first|second|third)$) - At this moment we are at the beginning of the test string. This position should not be immediately followed by (first or second or third) and then by the end of the string($)
.+ - matches 1+ occurrences of any character but not a newline character
$ - asserts the end of the string

edited Nov 11, 2017 at 11:02

answered Nov 11, 2017 at 10:46

Gurmanjot Singh

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1 Comment

Gurmanjot Singh Over a year ago

To the person who has down-voted, would you mind explaining your reason?

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