Docker build ARG always empty string

Question

I have a dockerfile here:

FROM golang:1.13-alpine as build
ARG DIR=somevalue
RUN echo $DIR

Output is

Sending build context to Docker daemon  57.37MB
Step 1/3 : FROM golang:1.13-alpine as build
 ---> 2e384b27f926
Step 2/3 : ARG DIR=somevalue
 ---> Running in 3cd3457a795f
Removing intermediate container 3cd3457a795f
 ---> ecfa2f50c4fa
Step 3/3 : RUN echo $DIR
 ---> Running in aab4e31e0e14

Removing intermediate container aab4e31e0e14
 ---> 5351cb77c245
Successfully built 5351cb77c245

DIR is always empty when I try DIR to another name example DIR1 it is empty too. Docker version is here

 Client:

 Version:           18.09.8
 API version:       1.39
 Go version:        go1.11
 Git commit:        2c0a67b
 Built:             Fri Sep  6 02:50:44 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server:

 Engine:
  Version:          18.09.6
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.11
  Git commit:       1d8275b
  Built:            Fri Sep  6 02:51:05 2019
  OS/Arch:          linux/amd64
  Experimental:     false

However, when I try to another machine, it is right, it will echo some value. Who can give me some tips to find the problem about the wrong machine? thanks.

Answer 1

This is obviously not the problem in your example, but I got this error when declaring an ARG before the FROM. Moving the ARG I needed below FROM resolved the problem.