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Brandon Yarbrough
Asked: 2013-09-26 09:07:52 +0800 CST

Dynamic logic in environment variable?

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I regularly invoke a particular remote server from a (Linux/bash) command line via tools like cURL or wget. This server requires an authentication token that expires every 10 minutes. I have a program that can generate a new token.

What I would like is an environment variable, $TOKEN, that I can use from the command line, that refreshes itself every 10 minutes, or, better yet, refreshes itself only when requested, and even then only every 10 minutes at most.

I was hoping that there was a way to tie an environment variable's evaluation to an executable, allowing me to do so with a script. Failing that, I was wondering if perhaps there was a way to set up a background process that updated the environment variable every 10 minutes.

linux

3 Answers

  1. You could set up a cron job that calls a script every 10 minutes (or whatever time interval you want). Then the script updates the variable.

    See: linux: how to permanently and globally change environment variables

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  2. you could create an alias to update the env var

    alias token='TOKEN=$(wget -q -O - http://webserver.com/TOKEN)'

    or

    alias token='TOKEN=$(/path/to/token-generator)'

    then, simply running "token" will set that var for current session

    you can add to your bash profile, so the alias remains accross logins

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  3. Store two environment variables, TOKEN and TOKEN_TIMESTAMP.

    if [ $(($(date +%s) - $TOKEN_TIMESTAMP)) -ge 600 ]; then
  /script/to/update/token.sh
  TOKEN_TIMESTAMP=$(date +%s) # this should be in the above script.
fi

/script/that/uses/token.sh # everything could be in this one script.

    This way you don't have to store logic in an environment variable [ew] or set up a cron job. The token is refreshed on-demand.

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