仅允许星形一次，不允许它与任何其他星形混合

Question

I have below regex. i want to validate like abcd,*,acd123 etc. I dont want * to be mixed with any like abc* and it should be allowed only once ex following should be rejected ** or *,*

/^([A-Za-z\d\/\*]+(,[A-Za-z\d\/\*]+)*)?$/.test(v)

valid:

ADSAD,*,adsad
*,adsds,asd123

Invalid:

**,asads
sasd,*,asa,*

Answer 1

Put the * out of the character classes and only allow it as an alternative to the alphanumeric or / symbols:

/^(?!.*\*.*\*)(?:(?:\*|[A-Za-z\d\/]+)(?:,(?:[A-Za-z\d\/]+|\*))*)?$/

See the regex demo

Details :

• ^ - start of string
• (?!.*\\*.*\\*) - a negative lookahead that fails the match once there are 2 * symbols in the string
• (?:(?:\\*|[A-Za-z\\d\\/]+)(?:,(?:[A-Za-z\\d\\/]+|\\*))*)? - an optional group (the whole string can be empty) matching:
  • (?:\\*|[A-Za-z\\d\\/]+) - a * ( \\* ) or ( | ) 1 or more alphanumeric or / symbols ( [A-Za-z\\d\\/]+ ), then followed with
  • (?:,(?:[A-Za-z\\d\\/]+|\\*))* - zero or more sequences of:
    • , - a comma
    • (?:[A-Za-z\\d\\/]+|\\*) - 1 or more alphanumeric or / symbols or a *
• $ - end of string.

Answer 2

I am not sure it will solve your whole problem, but the posted question can be solved this way:

^([^*]*,)?\*(,[^*]*)?$

where

• ^ is the start of the string;
• [^*] is any character that is not an asterisk.
  • Since we have [^*]*, , it means any number of characters that are not asterisks, followed by a comma;
  • ([^*]*,)? means we have zero or at most one of these in the string.
• \\* is the asterisk char. Since it is a special one, we need to escape it with \\ ;
• Again, we have `([^ ] ,)?
• $ means the end of the string.

Here is the result:

> /^([^*]*,)?\*(,[^*]*)?$/.test('abc,*,def')
true
> /^([^*]*,)?\*(,[^*]*)?$/.test('abc,def')
false
> /^([^*]*,)?\*(,[^*]*)?$/.test('abc,*,def,*,a')
false
> /^([^*]*,)?\*(,[^*]*)?$/.test('abc,*')
true
> /^([^*]*,)?\*(,[^*]*)?$/.test('*,abc')
true