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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, but this.isacat should be rejected.
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Any character (except for the newline character) will be matched by a period in a regular expression; when you literally want a period in a regular expression you need to precede it with a backslash. Many times you'll need to express the idea of the beginning or end of a line or word in a regular expression.
Definition and Usage. The ?! n quantifier matches any string that is not followed by a specific string n.
In the regex flavors discussed in this tutorial, there are 12 characters with special meanings: the backslash \, the caret ^, the dollar sign $, the period or dot ., the vertical bar or pipe symbol |, the question mark ?, the asterisk or star *, the plus sign +, the opening parenthesis (, the closing parenthesis ), the ...
Similarly, the negation variant of the character class is defined as "[^ ]" (with ^ within the square braces), it matches a single character which is not in the specified or set of possible characters. For example the regular expression [^abc] matches a single character except a or, b or, c.
You can use this regex: ^[^.]*$
^ - beginning of string[^.]* - any character except ., any number of repetitions$ - end of string
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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)
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