16

I have a shell script, script.sh, that writes some lines to a file:

#!/usr/bin/env bash
printf "blah 
blah 
blah 
blah\n" | sudo tee file.txt

Now in my Dockerfile, I add this script and run it, then attempt to add the generated file.txt:

ADD script.sh .
RUN chmod 755 script.sh && ./script.sh 
ADD file.txt .

When I do the above, I just get an error referring to the ADD file.txt . command:

lstat file.txt: no such file or directory

Why can't docker locate the file that my shell script generates? Where would I be able to find it?

pcsram
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2 Answers2

10

When you RUN chmod 755 script.sh && ./script.sh it actually execute this script inside the docker container (ie: in the docker layer).

When you ADD file.txt . you are trying to add a file from your local filesystem inside the docker container (ie: in a new docker layer).

You can't do that because the file.txt doesn't exist on your computer.

In fact, you already have this file inside docker, try docker run --rm -ti mydockerimage cat file.txt and you should see it's content displayed

John Smith
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michael_bitard
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1

It's because Docker load the entire context of the directory (where your Dockerfile is located) to Docker daemon at the beginning. From Docker docs,

The build is run by the Docker daemon, not by the CLI. The first thing a build process does is send the entire context (recursively) to the daemon. In most cases, it’s best to start with an empty directory as context and keep your Dockerfile in that directory. Add only the files needed for building the Dockerfile.

Since your text file was not available at the beginning, you get that error message. If you still want that text file want to be added to Docker image, you can call `docker build' command from the same script file. Modify script.sh,

#!/usr/bin/env bash
printf "blah 
blah 
blah 
blah\n" | sudo tee <docker-file-directory>/file.txt
docker build --tag yourtag <docker-file-directory>

And modify your Dockerfile just to add the generated text file.

ADD file.txt
.. <rest of the Dockerfile instructions>
techtabu
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    I think the outputted file may actually be in the Docker image layer itself. I think this may be the case because I removed the `ADD file.txt` line and replaced it with `CMD ["cat", "file.txt"]`. I was able to build the image and run the container correctly, with it displaying "blah blah bla.." – pcsram Jun 22 '16 at 19:15