SC2115

rm -rf "$STEAMROOT/"*

or

rm -rf /home/$(whoami)/*

rm -rf "${STEAMROOT:?}/"*

or

user=$(whoami)
rm -rf /home/${user:?}/*

If STEAMROOT is empty, this will end up deleting everything in the system's root directory.

Using :? will cause the command to fail if the variable is null or unset. Similarly, you can use :- to set a default value if applicable.

In the case of command substitution, assign to a variable first and then use :?. This is relevant even if the command seems simple and obviously correct, since forks and execs can fail due to external system limits and conditions, resulting in a blank substitution.

For more details about :? see the "Parameter Expansion" section of the Bash man page.

None.