Regular Expression for a string that should contain only one asterisk (*)

Question

String can contain anything, but must have one asterisk (*) throughout the string and that asterisk can be anywhere in the string.

Also string should not contain any blank spaces.

Following are valid strings:

test*
*_test
test*something

Following are invalid strings:

test_**
**_test
test*something*
test *something
test *
testsomething
*

Someone please help me writing a regex for the above scenario.

So it's a string that starts with zero or more non-asterisk characters, followed by a single asterisk, followed by zero or more non-asterisk characters? — Pointy, Apr 18 '16 at 13:06
Asterisk can be anywhere in the string.But, should have only one asterisk.If there is no asterisk in the string then it's invalid.Also, If there are more than one asterisk in the string then it's invalid.If there is one asterisk then it's a valid string it must return 'true' — Deve, Apr 18 '16 at 13:09
@AvinashRaj Your regex will allow whitespace. The regex mentioned before by me is correct. — Huso, Apr 18 '16 at 13:16
Guys, it should not allow asterisk alone.That means string must contain some characters. It can either before or after the asterisk. — Deve, Apr 18 '16 at 13:21

Kaspar Lee · Answer 1 · 2016-04-18T16:19:57.120

Use this RegEx:

^(?!(.*?\*){2,}|.*? |\*$).*?\*.*$

Live Demo on Regex101

If you want it to allow tabs (all other whitespace), use \s instead of a literal Space ():

^(?!(.*?\*){2,}|.*?\s|\*$).*?\*.*$

How it works:

^          # String starts with ...
(?!        # DO NOT match if ...
  (.*?\*)    # Optional Data followed by a *
  {2,}       # Multiple times (multiple *s)
  |          # OR
  .*?\s      # Optional Data followed by whitespace
  |          # OR
  \*$        # * then the end of the string (i.e. whole string is just a *)
)
.*?        # Optional Data before *
\*         # *
.*         # Optional Data after *
$          # ... String ends with

Demo:

strings = [
  'test*',
  '*_test',
  'test*something',
  'test',
  '*',
  'test_**',
  '**_test',
  'test*something*',
  'test *something',
  'test *'
]

for (var i = 0; i < strings.length; i++) {
  if (strings[i].match(/^(?!(.*?\*){2,}|.*?\s|\*$).*?\*.*$/)) {
    document.write(strings[i] + '<br>')
  }
}

You are currently incorrectly matching a string without asterisk, that should not be valid. — Sebastian Proske, Apr 18 '16 at 14:08
Thanks, I cannot believe I made much a silly mistake! Updated answer! — Kaspar Lee, Apr 18 '16 at 16:38

score 1 · Answer 2 · answered Apr 18 '16 at 13:15

1

You can use /^[^*\s]*\*[^*\s]*$/ to check for a string, that contains exactly one asterisk and no spaces. If only a single asterisk is invalid, you should add a lookahead to check for the presence of at leats two characters like /^(?=.{2})[^*\s]*\*[^*\s]*$/

See https://regex101.com/r/yE5zV2/1 for some samples (go to unit tests)

answered Apr 18 '16 at 13:15

Sebastian Proske

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`If only a single asterisk is invalid` ?? ur 1st regex is enough. – Avinash Raj Apr 18 '16 at 13:19
@AvinashRaj according to comments a string cotaining only a single asterisk should not match, so I included that. – Sebastian Proske Apr 18 '16 at 13:20

ismnoiet · Answer 3 · 2016-04-18T13:26:46.673

0

You can use this :

var regex = /^([^ \*]|\s)*\*{1}([^ \*]|\s)*$/

var str1 = '*abcfkdsjfksdjf';
var str2 = 'abcfkds*jfksdjf';
var str3 = 'abcfkdsjfksdjf*';
var str4 = 'abcfkdsjfksdjf';
var str5 = 'abcf*kdsjfk*sdjf';



console.log(regex.test(str1)); // returns true;
console.log(regex.test(str2)); // returns true;
console.log(regex.test(str3)); // returns true;
console.log(regex.test(str4)); // returns false;
console.log(regex.test(str5)); // returns false;

edited Apr 18 '16 at 13:26

answered Apr 18 '16 at 13:12

ismnoiet

4,129
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Maybe throw in some tests for multiple asterix or spaces? – SpoonMeiser Apr 18 '16 at 13:16
@SpoonMeiser check my updated answer, and thanks for your feedback by the way – ismnoiet Apr 18 '16 at 13:17
it should allow tabs.. – Avinash Raj Apr 18 '16 at 13:18
@AvinashRaj, thx for your feedback, now all the white space characters(\s) are matched except the space character. – ismnoiet Apr 18 '16 at 13:28

score 0 · Answer 4 · answered Apr 18 '16 at 22:20

The conditions hardly require any regex (good to use when checking for whitespace though).

// This is the checking function
function checkStr(x) {
  return (x.indexOf("*", x.indexOf("*")+1) === -1 && x.indexOf("*") > -1 && !/\s/.test(x));
}
// And this is the demo code
var valid = ["123*567", "*hereandthere", "noidea*"];
var invalid = ["123*567*", "*here and there", "noidea**", "kkkk"];
valid.map(x => document.body.innerHTML += "<b>" + x + "</b>: " + checkStr(x) + "<br/><b>");
invalid.map(x => document.body.innerHTML += "<b>" + x + "</b>: " + checkStr(x) + "<br/><b>");

The POI is return (x.indexOf("*", x.indexOf("*")+1) === -1 && x.indexOf("*") > -1 && !/\s/.test(x));:

x.indexOf("*", x.indexOf("*")+1) === -1 - makes sure there are no 2 asterisks
x.indexOf("*") > -1 - makes sure there is at least one *
!/\s/.test(x) - makes sure there is no whitespace in the string.

Regular Expression for a string that should contain only one asterisk (*)

4 Answers4