RegEx for single asterisk (*) and alphanumeric

Question

I need a javascript regex that accepts any alphanumeric character (can be any amount of characters or 0 characters if an asterisk is present) and a single asterisk anywhere in the string (but it does not need the asterisk).

Matches

*
abc
*abc
abc*
a*bc

Invalid Matches

**
*_abc
*abc*
abc**
**abc

I have

^([A-Za-z\d*]?)+$ 

but that matches multiple asterisks and I'm not sure how to only allow one https://regex101.com/r/a1C9bf/1

Answer 1

You may use this regex with a negative lookahead:

/^(?!(?:.*\*){2})[A-Za-z\d*]+$/gm

Updated RegEx Demo

Negative lookahead (?!(?:.*\*){2}) fails the match if there are more than one * in input.

Answer 2

Without requiring any look-ahead, you could use ^([\da-zA-Z]+|[\da-zA-Z]*\*[\da-zA-Z]*)$ https://regex101.com/r/xW2IvR/2

Answer 3

You could do:

^(?=.)[A-Za-z\d]*\*?[A-Za-z\d]*$

This will match any string that that's at least one character long ((?=.)), starts with zero or more alphanumeric characters, contains an optional *, and ends with zero or more alphanumeric characters.

You could also replace [A-Za-z\d] with [^\W_] to make it a little shorter (but slightly harder to read):

^(?=.)[^\W_]*\*?[^\W_]*$

Answer 4

You want one match one of two possible cases:

1. an asterisk surrounded by zero or more alphanumeric characters
2. one or more alphanumeric characters

Then this is your regex:

^([a-zA-Z\d]*\*[a-zA-Z\d]*|[a-zA-Z\d]+)$