You should use The RegexCoach and play around with the examples while checking and unchecking the options.
(i) -> case insensitive matching
/(cat.*?)(cat)(.*?)$/i
The Cat and the Cat?
If we use case insensitive matching it will not matter if ,,cat’’ is capitalized or not.
(s) -> single line matching
/(cat.*?)(cat)(.*?)$/is
the cat and
the cat?
The engine will do a multi line match without the need to put a \n. In this case the newline is included in the wildcard (dot). In other words the string is regarded as a single line even if it contains more than one line.
(m) -> multi line matching
(cat)(.*?)[\?]$
the cat and dog?
the cat?
cat?
The multi line option changes the behavior of the anchors ^ and $ . The will work for each line and not start and end of the whole string.
(x) -> exclude unescaped whitespaces
(cat)\s(.*?) [\?]$
the cat and dog?
We have an escaped whitespace \s and an unescaped space _ after the second group (). If you turn (x) on, the engine will ignore that there needs to be a space before the ?.
(g) -> match globally
(cat)(.*?)
the cat and dog?
cats and dogs
If you wand to use the expression several times on a string, you need to make it global. This will continue the match on the string after the first match. This is very useful if you use the match in a while context.
