Regex for not empty and not whitespace

Question

I am trying to create a regex that will return false if the String pattern contains whitespace or is empty. So far I have this

[^\s]

I think that will make sure the string does not contain whitespace but I am unsure of how to also check to make sure it is not empty. Any help would be appreciated.

You can use `str.length() == 0 || str.contains(" ")` for this. — Narendra Yadala, Nov 01 '11 at 13:49
@NarendraYadala, this will not match on tabs and other [whitespace characters](https://en.wikipedia.org/wiki/Whitespace_character). — Ro Achterberg, Aug 19 '19 at 12:29

Tony · Answer 1 · 2021-04-04T07:49:24.577

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In my understanding you want to match a non-blank and non-empty string, so the top answer is doing the opposite. I suggest:

(.|\s)*\S(.|\s)*

This matches any string containing at least one non-whitespace character (the \S in the middle). It can be preceded and followed by anything, any character or whitespace sequence (including new lines): (.|\s)*.

You can try it with explanation on regex101.

edited Apr 04 '21 at 07:49

answered Aug 29 '17 at 08:13

Tony

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After trying all of the varying answers I've found for this question, this one worked for me! – moth Sep 26 '17 at 20:50
I too don't understand why this isn't the best answer. It matches perfectly what the OP question asked for. – Richard Oct 01 '18 at 21:10
after some years it's time to answer that. it's easier and shorter to do it that way, also the condition is positive. It's good practice to formulate your conditions in a positive way and not in a negative. Note that a REGULAR EXPRESSION does not return anything. So the demand that a RE should return `false` is not fulfillable if you nitpick.. – Jan. Mar 27 '21 at 16:37
Thank you! I agree that the top answer is doing the opposite of what is asked. – Aaron Aug 02 '22 at 15:41

score 60 · Accepted Answer · answered Nov 01 '11 at 13:23

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/^$|\s+/ if this matched, there's whitespace or its empty.

answered Nov 01 '11 at 13:23

Jan.

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Correct. the + isn't needed. Just do not put a * there. ;) – Jan. Nov 01 '11 at 13:38
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In some languages (e.g. Ruby), `^` and `$` mean begining or end of the line, not string. But interesting fact is that even under this circumstances the expression will work correctly. – skalee Nov 30 '12 at 01:42
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@skalee There's a PCRE Modifier "m" which toggles multiline support – Jan. Dec 04 '12 at 14:06
@Jan Yes, but this regexp will work correctly even without this modifier because /^$/ will either match empty string or empty line in multiline string. And empty line => there's line break somewhere => whitespace. – skalee Dec 04 '12 at 15:52
In my case `/^$|\s+/ =~ " "` return 0 why ? – Giorgio Desideri Feb 05 '16 at 06:16
@GiorgioDesideri You should ask it on a new question, looks interesting why. – edmundo096 Mar 08 '16 at 13:16
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how would you invert this? I want it match if the string is not whitespace or empty – Dan Hastings Feb 10 '17 at 16:47
And How to avoid not empty string pls help me i have used following regex (?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=])(?=\\S+$).{8,15} – Coder Jun 15 '18 at 07:47
Please note that in PHP/PCRE this will need the `u` modifier to properly recognize [unicode whitespace](https://en.wikipedia.org/wiki/Whitespace_character#Unicode). – Ro Achterberg Aug 19 '19 at 12:40

score 25 · Answer 3 · answered Nov 01 '11 at 13:22

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Most regular expression engines support "counter part" escape sequences. That is, for \s (white-space) there's its counter part \S (non-white-space).

Using this, you can check, if there is at least one non-white-space character with ^\S+$.

PCRE for PHP has several of these escape sequences.

answered Nov 01 '11 at 13:22

Linus Kleen

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The regex is good, but the explanation is a bit misleading. Your regex matches a string that consists entirely of non-whitespace characters and is at least one character in length. Thus, it does more than just "check if there is at least one non-whitespace character". – Tim Pietzcker Nov 01 '11 at 13:39
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Why the downvote? The regex is solving the OP's problem - if it matches, the string is not empty and doesn't contain whitespace. – Tim Pietzcker Nov 01 '11 at 13:49
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This was the one for me. I simply did `str.match(/\S+/)` – Richard Ayotte May 21 '14 at 13:39
I tested this regex for the OP's request. It allows empty strings. They want to also exclude empty strings – Richard Oct 01 '18 at 21:06

score 10 · Answer 4 · answered Oct 28 '19 at 06:56

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/^$|\s+/ This matches when empty or white spaces

/(?!^$)([^\s])/ This matches when its not empty or white spaces

answered Oct 28 '19 at 06:56

Kam Hoe

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score 6 · Answer 5 · answered Sep 22 '14 at 15:59

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I ended up using something similar to the accepted answer, with minor modifications

(^$)|(\s+$)

Explanation by the Expresso

Select from 2 alternatives (^$)
    [1] A numbered captured group ^$
        Beginning of line ^
        End of line $
    [2] A numbered captured group (\s+$)
        Whitespace, one or more repetitions \s+
        End of line $

answered Sep 22 '14 at 15:59

oleksii

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You'll probably also want to mark these as non-capturing groups: `(?:^$)|(?:\s+$)` – Chaoix Jun 01 '17 at 18:26

score 6 · Answer 6 · answered Nov 21 '18 at 18:51

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A little late, but here's a regex I found that returns 0 matches for empty or white spaces:

/^(?!\s*$).+/

You can test this out at regex101

answered Nov 21 '18 at 18:51

TrieuNomad

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score -1 · Answer 7 · answered Nov 01 '11 at 13:25

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/^[\s]*$/ matches empty strings and strings containing whitespaces only

answered Nov 01 '11 at 13:25

micfra

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That's not what medium asked for. – Tim Pietzcker Nov 01 '11 at 13:36
You can remove the square brackets there. `/^\s*$/` will do the same task. – Narendra Yadala Nov 01 '11 at 13:37
@Narendra: Yes, but the question was to find strings that *contain* whitespace characters somewhere, not just *consist* of whitespace characters. – Tim Pietzcker Nov 01 '11 at 13:40
@TimPietzcker I see. Then `/^$|\s/` makes more sense as you pointed above. But I am not sure why would OP use regex for that, as `String` methods such as `str.length == 0 || str.contains(" ")` would be more handy in that case. – Narendra Yadala Nov 01 '11 at 13:46
@Narendra: The question "why regex?" is probably one of the most-asked questions in comments here on SO :) – Tim Pietzcker Nov 01 '11 at 13:50

Regex for not empty and not whitespace

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