Write a regular expression to reject strings containing a period

I'd like to find a regular expression that does not allow strings containing the "." character.

For example, this_is!a-cat should be accepted开发者_如何学Go, but this.isacat should be rejected.

You can use this regex: ^[^.]*$

1. ^ - beginning of string
2. [^.]* - any character except ., any number of repetitions
3. $ - end of string

Just match on the character and then negate the result:

my $str = 'this.isacat';
my $has_no_comma = !($str =~ !m/\./);

(Note that the above is in Perl, but the concept should work in any language)

^[^\.]*$

This defines a character class which matches all character except the dot. It also specified that the complete string from start to end much consist of character from this class.

/^(?!.*\.).+$/

Should do the trick. Use a negative look-ahead to disqualify anything with a period (remember, it needs to be escaped as a . in regex means any character).

Alternatively, you can create a class that matches any character but the period:

/^[^.]+$/

The [^ (characters) ] means "NOT (characters)".