[TIL] docker COPY không giống lệnh cp

Trong Dockerfile có lệnh (instruction) COPY dùng để copy file, thư mục. Nhưng cách hoạt động hơi khác lệnh cp trên UNIX.

cp file destdir

khi destdir là 1 thư mục đã tồn tại, cp sẽ copy file file tới destdir/file.

Còn COPY thì khác https://docs.docker.com/reference/dockerfile/#copy. Tất nhiên không ai đọc doc của syntax Dockerfile cả!

The COPY instruction copies new files or directories from and adds them to the filesystem of the image at the path You can specify multiple source files or directories with COPY. The last argument must always be the destination. If the destination path begins with a forward slash, it's interpreted as an absolute path, and the source files are copied into the specified destination relative to the root of the current build stage.

# create /abs/test.txt
COPY test.txt /abs/

Trailing slashes are significant. For example, COPY test.txt /abs creates a file at /abs, whereas COPY test.txt /abs/ creates /abs/test.txt.

If the destination path doesn't begin with a leading slash, it's interpreted as relative to the working directory of the build container.

WORKDIR /usr/src/app
# create /usr/src/app/rel/test.txt
COPY test.txt rel/

If destination doesn't exist, it's created, along with all missing directories in its path.

If the source is a file, and the destination doesn't end with a trailing slash, the source file will be written to the destination path as a file.

Khi build, COPY file destdir sẽ copy file, tạo 1 file mới tên là destdir.

Để có kết quả giống lệnh cp, cần thêm dấu / vào cuối destdir

COPY file destdir/

Trailing slashes are significant. For example, COPY test.txt /abs creates a file at /abs, whereas COPY test.txt /abs/ creates /abs/test.txt.

Kết luận

Hơi hơi giống không phải là giống, lệnh COPY có sự khác biệt khi thêm dấu / vào destination.

Hết.

HVN at https://pymi.vn and https://www.familug.org.

Ủng hộ tác giả 🍺