Why docker build error on copy?

[hooman-mirghasemi]

My docker file:
FROM wyveo/nginx-php-fpm:php73 COPY test.txt .

when run
docker build - < Dockerfile -t nnn

see this error:
`
failed to get console mode for stdin: The handle is invalid.
[+] Building 0.1s (7/7) FINISHED
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 634B 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/wyveo/nginx-php-fpm:php73 0.0s
=> [1/3] FROM docker.io/wyveo/nginx-php-fpm:php73 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 2B 0.0s
=> CACHED [2/3] WORKDIR /etc/nginx 0.0s
=> ERROR [3/3] COPY test.txt . 0.0s

[3/3] COPY test.txt .:

---

failed to compute cache key: "/test.txt" not found: not found
`

[hooman-mirghasemi]

finaly i found solution here:
https://serverfault.com/questions/666149/docker-copy-issue-no-such-file-or-directory

Note:

docker build - < Dockerfile does not have any context.

Hence use,

docker build .