Regex to match only if symbol in string used once

Question

Maybe it's a simple question but today i'm a bit stucked with it.

I need regex to match only if symbol % appeared once in a string..

for example:

/regexpForSymbol(%)/.test('50%') => true
/regexpForSymbol(%)/.test('50%%') => false

Thanks!

Why a regex? Just loop over the characers in the string and count... — fge, May 26 '13 at 18:44
http://stackoverflow.com/questions/4009756/how-to-count-string-occurrence-in-string — fejese, May 26 '13 at 18:47

Jerry · Accepted Answer · 2013-05-26T19:01:24.157

12

You could use:

^[^%]*%[^%]*$

The anchors are there to ensure every character is covered, and you probably already know what [^%] does.

edited May 26 '13 at 19:01

answered May 26 '13 at 18:45

Jerry

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You should use PCRE negation(!) , ^[!%}*%[!%]*$. Thanks. – Frank Aug 08 '16 at 13:00
@Frank That is not a valid syntax. – Jerry Nov 16 '16 at 09:48
i don't know for example. put a full explanation when you answer – mangusta May 01 '23 at 19:32
@mangusta I don't know... the expression is pretty simple if someone took the time to read the basics of regular expressions... `^` matches the start of string, `[^...]` is a negated class, `*` is a quantifier, and `$` matches the end of the string. The `%` is literal. – Jerry May 31 '23 at 06:34

melwil · Answer 2 · 2013-05-26T18:51:29.677

10

Here you go. Don't expect everyone to make these for you all the time though.

^      # Start of string
[^%]*  # Any number of a character not matching `%`, including none.
%      # Matching exactly one `%`
[^%]*  # 
$      # End of string

edited May 26 '13 at 18:51

answered May 26 '13 at 18:45

melwil

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That downvote was unnecessary. I'll gladly delete it if it's a duplicate. Just because it's a duplicate doesn't make it wrong in any way. – melwil May 26 '13 at 18:47
@Kosmetika I've explained the regex for you. This is pretty basic regex. If you like to use regex you should read up on it a bit. – melwil May 26 '13 at 18:51

score 1 · Answer 3 · answered May 26 '13 at 18:45

1

You don't need regex.

function checkIfOne(string, char) {
    return string.split(char).length === 2;
}

Usage:

var myString = "abcde%fgh",
    check = checkIfOne(myString, '%'); // will be true

answered May 26 '13 at 18:45

Niccolò Campolungo

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score 1 · Answer 4 · answered May 26 '13 at 18:53

1

You can use match and count the resulting array:

str.match(/%/g).length == 1

answered May 26 '13 at 18:53

David Hellsing

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Regex to match only if symbol in string used once

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