Calculate time of issue existing in Jira in line Script

[Andrei Lavrinovich]

i want to write Script that will calculate how long exist issue in jira. I don't know how to do it. I think that "currentDate-createdDate" (i don't even know how to do currentDate in jira, lol) will not working. I think that i must calculate days in all 12 month and calculate difference between two dates. Maybe exist not so painful method? And where can i find good tutorials for jira scripting. That what i found is for more knowledgeable people.