Cannot get a regex to work in JavaScript that allows whitespace and backslash

Question

I have a regular expression as below. It should allow alphabets, digits, round brackets, square brackets, backslash and following punctuation marks: period, comma, semi-colon, full colon, exclamation, percentage and dash.

^[(a-z)(A-Z) .,;:!'%\-(0-9)(\\)\(\)[\]\s]+$

Question : I have tried this regular expression with some text at this online tester: https://regex101.com/r/kO5tW2/2, but it always comes up with no matches. What is causing the expression to fail in above case? To me, the string being tested should come back as valid, but it's not.

Your expression did not work. Just click on the online test url and verify. It says 'no matches'. — Sunil
– Sunil, Commented Aug 21, 2015 at 1:20

score 1 · Accepted Answer · 2015-08-21 02:59:56Z

1

Your spec does not mention a question mark. However, the test text you give does include a question mark. You could have tested this easily enough by removing one character at a time from the test text until you got a match, which would have happened when you removed the question mark.

Either add the question mark to the regexp, or remove it from your test test.

Also, you do not need to (and should not) enclose ranges in parentheses.

In the below, I've also removed escaping for characters which do not need to be escaped:

^[a-zA-Z .,;:!'%\-0-9\\()[\]\s?]+$
                              ^

https://regex101.com/r/kO5tW2/4

edited Aug 21, 2015 at 2:59

answered Aug 21, 2015 at 2:47

user663031

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6 Comments

Sunil Over a year ago

Great. Thanks so much. I am just verifying it in my aspx page.

Sunil Over a year ago

Thanks. The expression you gave works perfectly. Would \" be for allowing double quotes as well?

Sunil Over a year ago

When I use this expression in an aspx page I need to put it as Expression="^[a-zA-Z .,;:!'%\-0-9\()[]\s?]+$". So just putting a double quote in above results in parsing error at run time.

Sunil Over a year ago

If I use " in place of " then the expression works to allow double quotes. Expression="^[a-zA-Z .,;:!'%\-0-9()[]\s?;quot;]+$"

Sunil Over a year ago

In ASP.Net aspx page, we need to use " but in JavaScript we could just use double quotes as you suggested.

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Maksym Kozlenko · Accepted Answer · 2015-08-21 01:27:01Z

1

Try adding m (multiline) modifier to regex

If you have a string consisting of multiple lines, like first line\nsecond line (where \n indicates a line break), it is often desirable to work with lines, rather than the entire string. Therefore, all the regex engines discussed in this tutorial have the option to expand the meaning of both anchors. ^ can then match at the start of the string (before the f in the above string), as well as after each line break (between \n and s). Likewise, $ still matches at the end of the string (after the last e), and also before every line break (between e and \n). Source

edited Aug 21, 2015 at 1:27

answered Aug 21, 2015 at 1:16

Maksym Kozlenko

10.4k2 gold badges69 silver badges55 bronze badges

5 Comments

Sunil Over a year ago

Should not \s match all white space character like \n, so why is the multi-line modifier needed?

Maksym Kozlenko Over a year ago

By default regex will match $ with end of line, not end of string

Sunil Over a year ago

So will the multi-line expression be: ^[(a-z)(A-Z) .,;:!'%\-(0-9)(\)()[]\s]+$/gm

user663031 Over a year ago

Well, this will not work. It will match lines within the input text, but not match the entire input text, which is presumably what the OP wants.

slebetman Over a year ago

@Sunil: You have multiple redundant ( and ) in your regex.

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