Passing profiles to Docker via Environment Vars fails if the profile uses local variables

[ghost]

Description of Problem, Request, or Question

Defining and using local variables inside profiles is supported according to this link:
https://docs.conan.io/en/latest/reference/profiles.html#variable-declaration

The content of a profile will be encoded in environment variables that are then passed to the Docker command.
If the profile contains a $, it will not be escaped. The shell inside the Docker container then sets these variables and tries to evaluate everything following the $ as an environment variable as well.

Example:

The profile

compiler_version=7
[env]
CC=gcc-$compiler_version

will be encoded into

compiler_version=7@@[env]@@CC=gcc-$compiler_version@@

Inside the container the shell will treat the $compiler_version part as an undefined variable and will replace it with an empty string. That results in a profile like this:

compiler_version=7
[env]
CC=gcc-

where the version number is missing in the definition of `CC``.

Environment Details

• Conan Package Tools Version: 0.35.0
• Operating System: Linux
• Operation System Version: Ubuntu 20.04
• Compiler+version: any
• Docker image: based on ubuntu:18.04
• Conan version: conan 1.33.1
• Python version: python 3.8.5

Steps to reproduce (Include if Applicable)

Build logs (Include if Available)

[ghost]

I am not sure if other character in profiles can also cause problems when stored in environment variables.
Maybe this issue can be solved by switching to a different encoding. Something like BASE64 encoding should work with environment variables although it will be incompatible with the current implementation.