Dynamic environment variables in Linux?

Question

Is it possible in some way to have dynamic environment variables in Linux?

I have a webserver where sites follow this layout:

site/
    qa/
    production/

I would like to have an environment variable (e.g. APPLICATION_ENV) that is set to "qa" when I'm in the qa directory, and to "production" when I'm in the production directory. The reason for this is that various sites can use many different processes that all need to know if it's the QA or production environment. Some sites use PHP under Apache, some use Node.js, some sites come with commandline tools, cron jobs, etcetera. I would like to have one authorative source on whether it's a QA or a production environment.

Answer 1

Based on rvm's override:

cd () { 
    if builtin cd "$@"
    then
        if [[ "$PWD" =~ /(qa|production)(/|$) ]]
        then
            export APPLICATION_ENV="${BASH_REMATCH[1]}"
        else
            unset APPLICATION_ENV
        fi
        return 0
    else
        return $?
    fi
}

Just put this function in .bashrc or some other sourced environment file, and try to cd into qa, production, or one of their subdirectories.

Answer 2

You can create an executable script in one of /bin or /usr/bin directories and execute it from the site scripts. I don't see why you need to hack cd.

/usr/bin/which-version:

#!/bin/bash
if [[ "$PWD" =~ /(qa|production)(/|$) ]]
then
  echo "${BASH_REMATCH[1]}"
else
  echo "unknown"
fi

web-site:

$env = system("which-version")