regular expression to match a character that can only appear once in a string?

问题

I'm looking for a regular expression that will match if the string contains the character *, but only once. It should match a*aa, aa*aaaaa, a*aaaa, but it should not match a**a, a****, ****. any advice?

回答1:

You can try this pattern:

^[^*]*\*[^*]*$

Explanations:

^      begining of the string
[^*]*  all characters except * zero or more times
\*     literal *
[^*]*  all characters except * zero or more times
$      end of the string

回答2:

It doesn't appear as though you're capturing any of this string -- so why use a regex to begin with? tr// will return the number of matches:

my $nStars = ( $str =~ tr/*/*/ );

回答3:

You could use the split function with /\*/. If the length of the returned array is 2, it means that you have a single *.

来源：https://stackoverflow.com/questions/17869299/regular-expression-to-match-a-character-that-can-only-appear-once-in-a-string