以存在条件为条件捕获群体

Question

I have url like

http://localhost:8080/web/group/555/content/777/image?arg1=1&arg2=2#anchor

There are 3 parts i'm trying to get: group number , content number and the view type value which is "image" in the sample above (can be one of predefined set of values and it is guarateed no values with text "group" or "content").

I got following regexp so far (it has 3 capturing groups i need)

/.*(?:\/group\/([\d]+))(?:\/content\/([\d]+))\/([\w]+).*/g

which works only when all the parts are present.

The problem is any of the part can be absent (except "view type"), so next urls are also valid:

http://localhost:8080/web/content/777/image
// which has $1="", $2="777", $3="image"
http://localhost:8080/web/nogroup/555/content/777/video
// which has $1="", $2="777", $3="video"
http://localhost:8080/web/audio
// which has $1="", $2="", $3="audio"

Is there a way to tell regexp: if there is no matching for the group $1 set its value to ""?

Answer 1

You need to add a question mark ? after each of the groups that can be present but aren't necessary for a match and it will automatically populate them with "" :

/.*(?:\/group\/([\d]+))?(?:\/content\/([\d]+))?\/([\w]+).*/g