We can temporarily save variables in our local environment using the export command like so:
$ export MYNAME="Billy"
$ echo $MYNAME
Billy
$ echo "$MYNAME is hungry 🤤"
Billy is hungry 🤤
As you can see above, to invoke the variable, we use the $ sign followed by the variable name. If we close this terminal session, the variable MYNAME will be lost.
There are however built-in variables that are always available. These will vary depending on your operating system and environment. To see all that are available at any time, you can use the printenv command.
To search for a specific variable, you can pipe the printenv into grep like so:
printenv | grep MYNAME
MYNAME=Billy