How do you print to console from a docker file during build?

Question

Suppose you have some Dockerfile. What needs to be added to that file such that a string (ie "Hello World") is printed to the console during build?

docker build .

RESEARCH

This question is a top hit in Google for this topic. I have researched by googling and landing here.

WHAT I HAVE TRIED

From the accepted answer:

RUN echo "hello there"

This actually doesn't work.

What research did you do? What have you tried? What documentation did you read? — KamilCuk, May 14 '21 at 21:14
I guess you can add `RUN echo "Hello World"` in your Dockerfile. Is this what you want ? — norbjd, May 15 '21 at 13:24
Possible duplicate: [Docker build not showing any output from commands](https://stackoverflow.com/q/64804749/596285) — BMitch, May 15 '21 at 15:30

Noam Yizraeli · Accepted Answer · 2022-11-25T14:02:44.500

52

It's fairly simple actually. If you just want to print stuff using in the build proccess you could just add the following line to your Dockerfile:

RUN echo "hello there"

And then add these options to your docker build command:

--progress=plain --no-cache

EDIT:

as noted by @SoftwareEngineer, when used for logging or tooling purposes you should append the echo command to the one you want to check if were successful. for example when downloading packages and wanting to get a print statement when finished: example from nginx official image dockerfile

RUN apt-get install -y whatever && echo "installed package"

edited Nov 25 '22 at 14:02

answered May 15 '21 at 15:22

Noam Yizraeli

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Though, I wouldn't recommend actually doing this – Software Engineer May 15 '21 at 15:29
1

I agree it's a bit odd to say the least but other than it's not best practice, why wouldn't you recommend this @SoftwareEngineer ? for testing purposes for example – Noam Yizraeli May 15 '21 at 15:32
3

Sorry, I should have been a little clearer. My objection is to running this in its own `RUN` command and creating an extra layer just to produce output. For debugging and audit purposes there is nothing intrinsically wrong with producing logging output. I just wouldn't recommend doing it in this specific way. – Software Engineer May 15 '21 at 15:38
2

The --progress=plain --no-cache is key. – Daniel Viglione Nov 29 '22 at 12:17
@DanielViglione what OS and docker installation method are you using? – Noam Yizraeli Nov 30 '22 at 13:17

score 0 · Answer 2 · answered Apr 20 '23 at 16:53

I like to keep notes to remind myself what I am doing and display logs to myself to verify that it happens in this version. RUN it is

# Copy local config into container
COPY config/kibana.yml /opt/kibana/config/kibana.yml

# Verify that local configuration file is copied in & enables SSL/TLS
RUN ls -l /opt/kibana/config/

How do you print to console from a docker file during build?

2 Answers2

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