How do I edit a file after I shell to a Docker container?

Question

I successfully shelled to a Docker container using:

docker exec -i -t 69f1711a205e bash

Now I need to edit file and I don\'t have any edito

Answer 1

You can also use a special container which will contain only the command you need: Vim. I chose python-vim. It assumes that the data you want to edit are in a data container built with the following Dockerfile:

FROM debian:jessie
ENV MY_USER_PASS my_user_pass
RUN groupadd --gid 1001 my_user
RUN useradd -ms /bin/bash --home /home/my_user \
            -p $(echo "print crypt("${MY_USER_PASS:-password}", "salt")" | perl) \
            --uid 1001 --gid 1001 my_user
ADD src /home/my_user/src
RUN chown -R my_user:my_user /home/my_user/src
RUN chmod u+x /home/my_user/src
CMD ["true"]

You will be able to edit your data by mounting a Docker volume (src_volume) which will be shared by your data container (src_data) and the python-vim container.

docker volume create --name src_volume
docker build -t src_data .
docker run -d -v src_volume:/home/my_user/src --name src_data_1 src_data
docker run --rm -it -v src_volume:/src fedeg/python-vim:latest

That way, you do not change your containers. You just use a special container for this work.

Answer 2

Sometime you must first run the container with root:

docker exec -ti --user root <container-id> /bin/bash

Then in the container, to install Vim or something else:

apt-get install vim

Answer 3

An easy way to edit a few lines would be:

echo "deb http://deb.debian.org/debian stretch main" > sources.list

Answer 4

See Stack Overflow question sed edit file in place

It would be a good option here, if:

1. To modify a large file, it's impossible to use cat.

2. Install Vim is not allowed or takes too long. My situation is using the MySQL 5.7 image when I want to change the my.cnf file, there is no vim, vi, and Vim install takes too long (China Great Firewall). sed is provided in the image, and it's quite simple. My usage is like

   sed -i /s/testtobechanged/textwanted/g filename

   Use man sed or look for other tutorials for more complex usage.

Answer 5

You can use cat if it's installed, which will most likely be the case if it's not a bare/raw container. It works in a pinch, and ok when copy+pasting to a proper editor locally.

cat > file
# 1. type in your content
# 2. leave a newline at end of file
# 3. ctrl-c / (better: ctrl-d)
cat file

cat will output each line on receiving a newline. Make sure to add a newline for that last line. ctrl-c sends a SIGINT for cat to exit gracefully. From the comments you see that you can also hit ctrl-d to denote end-of-file ("no more input coming").

Another option is something like infilter which injects a process into the container namespace with some ptrace magic: https://github.com/yadutaf/infilter

Answer 6

If you don't want to add an editor just to make a few small changes (e.g., change the Tomcat configuration), you can just use:

docker cp <container>:/path/to/file.ext .

which copies it to your local machine (to your current directory). Then edit the file locally using your favorite editor, and then do a

docker cp file.ext <container>:/path/to/file.ext

to replace the old file.