How do I call a function from a shell script in Docker?

Question

I'm trying to call a function runaudit inside of of my docker container.

The shell script, which contains the runaudit function, is copied inside of the image and the BASH_ENV environment variable is set to point to /etc/audittools/audit.sh

My question is, how do run this runaudit function inside of my container?

I tried to run it inside the container but I get the following message.

/ # runaudit
/bin/sh: runaudit: not found

The ENV output is showing me that the environment variable has been set.

Herewith the Dockerfile and small shell function.

NOTE : The real function is much larger and I need to keep it maintained inside of it's own file.

I appreciate any advice or help with this.

Dockerfile

FROM alpine:3.10

MAINTAINER acme

ARG VERSION=0.3.0

RUN apk add --no-cache curl tar gettext libintl

RUN envsubst --version

RUN mkdir -p /etc/audittools

COPY audit.sh /etc/audittools

RUN chmod a+x /etc/audittools/audit.sh

ENV BASH_ENV "/etc/audittools/audit.sh"

Shell Script - audit.sh

#!/usr/bin/env sh
function runaudit() {
    echo "Hello World"
}

Run the function

docker run -it test /bin/sh runaudit

David Maze · Accepted Answer · 2019-08-19 09:47:24Z

2

Change this to be an ordinary shell script; in generic programming terms, make it a "program" and not a "function".

Remember that docker run starts a new container with a clean environment, runs whatever its main program is, and then exits. Also remember that the difference between a shell script and a shell function is that a function runs in the context of its calling shell and can change environment variables and other settings, whereas a shell script runs in a new shell environment; but since in a docker run context the parent shell environment is about to get torn down, it doesn't matter.

So I'd change the shell script to

#!/bin/bash
# ^^^ use the standard shell location
# vvv remove the function wrapper
echo "Hello World"

and then change the Dockerfile to run it on startup

...
COPY audit.sh /etc/audittools
RUN chmod a+x /etc/audittools/audit.sh
CMD ["/etc/audittools/audit.sh"]

answered Aug 19, 2019 at 9:47

David Maze

165k47 gold badges262 silver badges301 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Chesneycar Over a year ago

Hi David, Thanks for posting your answer. Unfortunately I need to expose the audit function for the other containers I use in Kubernetes. My Jenkins CI/CD pipeline utilises different containers as part of it's build stage.

David Maze Over a year ago

You cannot expose functions in Docker (or Kubernetes) this way (again, as a general programming statement, not specific to shell functions). Most notably your docker run would audit a new empty container containing only the audit script. Your CI system (probably the per-image Dockerfile) needs to copy the script into the images that are being built.

LinPy · Accepted Answer · 2019-08-19 09:01:00Z

2

you can run it like this:

docker run -ti test sh -c "source /etc/audittools/audit.sh && runaudit"

answered Aug 19, 2019 at 9:01

LinPy

18.8k5 gold badges47 silver badges63 bronze badges

Comments

Chandrahas Gaikwad · Accepted Answer · 2023-01-13 13:07:52Z

0

I tried with the CMD command and it worked fine for me from inside the dockerfile.

CMD ["/etc/audittools/audit.sh", "runaudit"]

You can add this line post the chmod for audit.sh. Your final dockerfile will look something like:

FROM alpine:3.10

MAINTAINER acme

ARG VERSION=0.3.0

RUN apk add --no-cache curl tar gettext libintl

RUN envsubst --version

RUN mkdir -p /etc/audittools

COPY audit.sh /etc/audittools

RUN chmod a+x /etc/audittools/audit.sh

ENV BASH_ENV "/etc/audittools/audit.sh"

CMD ["/etc/audittools/audit.sh", "runaudit"]

answered Jan 13, 2023 at 13:07

Chandrahas Gaikwad

2111 gold badge4 silver badges14 bronze badges

Collectives™ on Stack Overflow

How do I call a function from a shell script in Docker?

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related