Setting environment variable for docker container at runtime

Question

I have a requirement to set the environment variable for docker container at runtime. The value can only be determined at runtime by combination two other variables which are available at runtime. In a simpler form, the following is not working.

docker run -ti -e host="name" -e port="123" centos:7 bash -c "export url=$host:$port; env"

returns the following where url is empty when the value of $host and $port is available to construct $url ?

...
host=name
url=:
port=123
...

that other guy · Accepted Answer · 2020-07-02 04:35:11Z

2

You have to single quote the shell command to avoid your interactive shell expanding the variable before the docker shell sees them:

docker run -ti -e host="name" -e port="123" centos:7 bash -c 'export url=$host:$port; env'

With single quotes, your shell will pass export url=$host:$port; env to Docker.

With double quotes, your current shell will first dutifully expand the variables, and therefore just pass url=:; env

answered Jul 2, 2020 at 4:35

that other guy

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Dexter Over a year ago

this works. I thought my question had an example of simplified form of problem that I am facing. Actually, I have a dockerfile with a custom entrypoint. This environment variable $host should be available in container. I can confirm from the logs that the $url is set during the start up of container. But when I bash into the container, this variable is empty.

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