updatecomment.groovy

package examples.answers

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.Issue
import com.atlassian.jira.issue.comments.Comment

def commentManager = ComponentAccessor.getCommentManager()

def thisComment = transientVars["comment"]
Issue issue = issue

if (thisComment) {
    def comments = commentManager.getComments(issue)

    def lastComment = comments.last() as Comment
    // update the comment
    commentManager.update(lastComment, false)
}