If I run

FOO=bar

That environment variable is not persisted in my environment for later commands.

echo $FOO
 

But if I run

FOO=bar;

Then the variable is always available until I unset FOO

echo $FOO
bar

unset FOO
echo $FOO
  

I expect this behavior with export FOO=bar but why does that happen with ; too?

If I run

FOO=bar docker run -it -e FOO=$FOO debian env

That environment variable is not set in the command output for the env command.

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=03f3b59c0aab
TERM=xterm
FOO=
HOME=/root

But if I run

FOO=bar; docker run -i -t --rm -e FOO=$FOO debian:stable-slim env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=672bfdcde93c
TERM=xterm
FOO=bar
HOME=/root

Then the variable is available from the container and also exported into my current shell environment.

echo $FOO
bar

I expect this behavior with export FOO=bar but why does that happen with ; too?