what exactly env command do?

Question

i recently came across the shellshock bug, which is a bug in the bash shell. somehow it uses the env command to create environment variables containing functions.

$ env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

These functions then run when a new bash shell is spawned. i read at many places and got the same explanation that i just wrote. But i still cannot make out the working of the above command along with its parameters. can anyone explain?

Answer 1

env sets one or more environment variables and then runs the remaining arguments as a command.

It's not significantly different from the following syntax:

x='() { :;}; echo vulnerable' bash -c "echo this is a test"

One thing env can do (although the feature is not used in the above example) is create a clean environment; if the first option to env is a single - (or -i), then the environment is cleaned before doing the explicit assignments and running the command.