How to define a variable in a Dockerfile?

variables docker dockerfile
Maxime picture Maxime · Nov 26, 2015 · Viewed 150.5k times · Source

In my Dockerfile, I would like to define variables that I can use later in the Dockerfile.

I am aware of the ENV instruction, but I do no want these variables to be environment variables.

Is there a way to declare variables at Dockerfile scope?

Answer

lumos0815 picture lumos0815 · Jun 5, 2016

You can use ARG - see https://docs.docker.com/engine/reference/builder/#arg

The ARG instruction defines a variable that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag. If a user specifies a build argument that was not defined in the Dockerfile, the build outputs an error.

Related questions

How can I determine if a variable is 'undefined' or 'null'?

How do I determine if variable is undefined or null? My code is as follows: var EmpName = $("div#esd-names div#name").attr('class'); if(EmpName == 'undefined'){ // DO SOMETHING }; <div id="esd-names"> <div id="name"></div&…

Read More
"Notice: Undefined variable", "Notice: Undefined index", and "Notice: Undefined offset" using PHP

I'm running a PHP script and continue to receive errors like: Notice: Undefined variable: my_variable_name in C:\wamp\www\mypath\index.php on line 10 Notice: Undefined index: my_index C:\wamp\www\mypath\index.php on line 11 Line 10 …

Read More
JavaScript check if variable exists (is defined/initialized)

Which method of checking if a variable has been initialized is better/correct? (Assuming the variable could hold anything (string, int, object, function, etc.)) if (elem) { // or !elem or if (typeof(elem) !== 'undefined') { or if (elem != null) {

Read More