why get error: "docker build" requires exactly 1 argument

Question

I look a sample

Dockerfile

ARG some_variable_name
# or with a default:
# ARG some_variable_name=default_value

RUN echo "Oh dang look at that $some_variable_name
# or with ${some_variable_name}

docker build

$ docker build --build-arg some_variable_name=a_value

result

Oh dang look at that a_value

but, I used the sample always gets error

"docker build" requires exactly 1 argument.
See 'docker build --help'.

Usage:  docker build [OPTIONS] PATH | URL | -

Build an image from a Dockerfile

Why? Was I lose something?

question from:https://stackoverflow.com/questions/65650924/why-get-error-docker-build-requires-exactly-1-argument

Answer 1

You seem to have forgotten to put a dot, which represents that the Dockerfile in the local directory.

By that I meant:

docker build -t mytag .

What you were previously doing was:

docker build -t mytag

Thus forgetting to put the dot.