I'm new using environment variables and i'm testing how to pass and override environment vars to my scripts.
To test its behaviour, i've created a simple trivial script named testenv.sh as follow:
#!/bin/bash echo $COLOR So, when i run
$ env COLOR=RED ./testenv.sh I get the expected stdout RED.
However my question is, why if i run the following command
$ env COLOR=RED echo $COLOR I don't get the same result as above, in fact is a blank stdout.
$COLOR is expanded by the shell before env calls /bin/echo.
This cannot work unless you let env call a shell script that expands the variable.
Even:
COLOR=RED echo $COLOR does not work as you expect since Shell Variables are expanded before the new environment is set up.
You need to split this into two lines:
COLOR=RED echo $COLOR to make it work as you expect.
If you call:
env COLOR=RED sh -c 'echo $COLOR' it works because the single quotes prevent variable expansion and the variable expansion is delayed for the time when the new shell is run with the new environment.
env. shell vars and not env. It works !