Javascript regexp - only if first character is not an asterisk

Question

I am using a javascript validator which will let me build custom validation based on regexp

From their website: regexp=^[A-Za-z]{1,20}$ allow up to 20 alphabetic characters.

This will return an error if the entered data in the input field is outside this scope.

What I need is the string that will trigger an error for the inputfield if the value has an asterix as the first character.

I can make it trigger the opposite (an error if the first character is NOT an asterix) with:

regexp=[\u002A]

Heeeeelp please :-D

Dugald

Answer 1

How about:

^[^\*]

Which matches any input that does not start with an asterisk; judging from the example regex, any input which does not match the regex will be cause a validation error, so with the double negative you should get the behaviour you want :-)

Explanation of my regex:

• The first ^ means "at the start of the string"
• The [ ... ] construct is a character class, which matches a single character among the ones enclosed within the brackets
• The ^ in the beginning of the character class means "negate the character class", i.e. match any character that's not one of the ones listed
• The \* means a literal *; * has a special meaning in regular expressions, so I've escaped it with a backslash. As Rob has pointed out in the comments, it's not strictly necessary to escape (most) special characters within a character class

Burrus

you don't need to escape the * inside [] – Sanity

@Rob: You're probably right. I've found that it depends on the platform, but I've never had any problems explicitly escaping using a backslash – Burrus

fair enough, I was only being pedantic because you got your answer in first :P – Sanity

@Rob: FGIW syndrome, sorry ;-) In any case, it's good for others to know that escaping inside a character class is usually unnecessary – Burrus

Actually this will trigger an validation error if there is an asterix anywhere in the input value, not only if the first character is an asterix... – Dugald

@Splynx: Are you sure you included the first ^ (which anchors the rest of the regex to the beginning of the string)? The regex should only ever match a non-empty input with the first character not being a * – Burrus

My bad, it did in fact only check on the first character it seems - any ways it validates just like it should - thank you again! – Dugald

@Splynx: No problem ;-) By the way, if you need it to pass an empty input as valid too, you can use: ^(?:[^\*]|$) – Burrus

Answer 2

How about ^[^\*].+.

Broken down:

• ^ = start of string.
• [^\*] = any one character not the '*'.
• .+ = any other character at least once.

Bullivant

This is better answer IMO. – Leis

Answer 3

You can invert character class by using ^ after [

regexp=[^\u002A]

Queenstown