Copying files to and from containers in Docker - Step-by-Step Execution

Process Flow - Copying files to and from containers

Start

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Choose source: Host or Container

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Choose destination: Container or Host

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Run docker cp command

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File copied successfully

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End

This flow shows how to copy files either from the host to a container or from a container to the host using the docker cp command.

Execution Sample

Docker

docker cp ./hostfile.txt mycontainer:/app/containerfile.txt

docker cp mycontainer:/app/containerfile.txt ./hostfile_copy.txt

Copies a file from the host to the container, then copies it back from the container to the host with a new name.

Process Table

Step	Command	Source	Destination	Action	Result
1	docker cp ./hostfile.txt mycontainer:/app/containerfile.txt	Host ./hostfile.txt	Container /app/containerfile.txt	Copy file from host to container	File copied inside container at /app/containerfile.txt
2	docker cp mycontainer:/app/containerfile.txt ./hostfile_copy.txt	Container /app/containerfile.txt	Host ./hostfile_copy.txt	Copy file from container to host	File copied on host as ./hostfile_copy.txt
3	-	-	-	-	Process complete, files copied successfully

💡 All copy commands executed successfully, no errors

Status Tracker

Variable	Start	After Step 1	After Step 2	Final
hostfile.txt	Exists on host	Exists on host	Exists on host	Exists on host
containerfile.txt	Does not exist	Exists in container at /app/containerfile.txt	Exists in container at /app/containerfile.txt	Exists in container
hostfile_copy.txt	Does not exist	Does not exist	Exists on host	Exists on host

Key Moments - 3 Insights

Why do we specify container name and path with a colon in the docker cp command?

The colon separates the container name from the file path inside the container, telling docker where to copy the file. See execution_table step 1 and 2 for examples.

Can we copy directories with docker cp the same way as files?

Yes, docker cp supports copying directories recursively. The command syntax is the same, just specify the directory path instead of a file.

What happens if the destination file already exists?

The docker cp command overwrites the destination file without warning. This is shown in the execution_table where the file is copied back to the host with a new name to avoid overwriting.

Visual Quiz - 3 Questions

Look at the execution table, what is the source in step 2?

A Host ./hostfile.txt

B Container /app/containerfile.txt

C Host ./hostfile_copy.txt

D Container /app/hostfile.txt

💡 Hint

Check the 'Source' column in execution_table row for step 2

At which step does the file first appear inside the container?

A Step 2

B Step 3

C Step 1

D It never appears inside the container

💡 Hint

Look at the 'Result' column in execution_table for when the file is copied inside container

If you want to copy a directory instead of a file, what changes in the command?

A No change, just specify directory path

B Use docker copy instead of docker cp

C Add -r flag to docker cp

D Use docker cp with --dir option

💡 Hint

Refer to key_moments about copying directories

Concept Snapshot

docker cp <source> <destination>
- Copies files or directories between host and container
- Use containerName:/path for container paths
- Overwrites destination without warning
- Supports both directions: host->container and container->host

Full Transcript

This lesson shows how to copy files to and from Docker containers using the docker cp command. You specify the source and destination paths, using containerName:/path syntax for container files. The command works both ways: copying from host to container and from container to host. Files are overwritten if the destination exists. Directories can also be copied by specifying their paths. The execution table traces two commands: copying a file into the container, then copying it back out with a new name. Variables track file existence on host and container after each step. Key moments clarify the colon syntax, directory copying, and overwriting behavior. The quiz tests understanding of source/destination and command usage.