Copy file

COPY [--chown=<user>:<group>] <src>... <dest>

COPY package.json package-lock.json ./
COPY --chown=appuser:appuser . /app/

Note COPY only handles local files from the build context. Copy dependency manifests (package.json, requirements.txt) before the rest of the source code so that dependency-install layers are cached when only your application code changes.

docker cp <container>:<path> <host_path>
docker cp <host_path> <container>:<path>

docker cp web-api:/app/logs/error.log ./error.log
docker cp ./hotfix.js web-api:/app/hotfix.js

Note Works on both running and stopped containers. Useful for extracting crash logs or injecting a config file for debugging. Changes via cp do not persist across container recreation — use volumes for anything permanent.

cp [options] source destination

cp config.yml config.yml.bak
cp -r templates/ /opt/app/templates/
cp -i report.csv ~/Desktop/

Note -r is required for directories (recursive copy). -i prompts before overwriting. Without -i, cp silently overwrites the destination. Use -a to preserve permissions, timestamps, and symlinks.

with open(path, 'rb') as f:
    data = f.read()

# Copy a binary file
with open("image.png", "rb") as src:
    data = src.read()

with open("copy.png", "wb") as dst:
    dst.write(data)

print(f"Copied {len(data)} bytes")

Note Use 'rb' / 'wb' modes for binary files (images, archives, etc.). Never open binary files in text mode; it corrupts the data on some platforms.