One of the things I have learned from helping at Stack Overflow (and I say that as someone who helps 90% of the time and seeks help 10% of the time) is that sad-face-begging is counterproductive. Readers, rightly or wrongly, will read that either as blame or blackmail, neither of which is a productive way to ask for assistance.
So, what I would suggest is:
put on your positive thinking hat
explain something about your use case (if only because “+1 me too fix it for me” is not likely to encourage replies)
remember that CI is hard, and requires some familiarity with console commands, permissions, installing things, etc.
Your base image is docker:17.06.1-ce-git, and I assume that’s based on Ubuntu. If so, I imagine it would have curl installed, but maybe not. Have you tried installing curl in the usual way, prior to trying to use it?
Thank you for the reply and your suggestion for the community is great.
I showed a sad-face-begging because the document really needs to improve, I invested lots of time to get to work with CircleCI 2.0 docker mode.
At first, I thought the image should be based on Ubuntu as you, however, at last, I get to know that the docker:17.06.1-ce-git is based on Alpine after serval times of failure and blind working.
So I use apk update && apk add curl curl-dev bash to get my curl, the problem solved.
Sure, I understand that you believe that. But I helped you despite your question, not because of it. We won’t know how many people skipped your question for the reasons I outlined (and to be fair, this forum is pretty quiet anyway) but my advice stands. Exuding a positive frame of mind encourages people to help.