Shell Programming and Scripting

Me dumb. Can't get this to work...

#!/bin/sh
export JAVA_HOME_BAK=${JAVA_HOME}
or
#!/bin/sh
export JAVA_HOME_BAK=/usr/java
or
#!/bin/sh
export JAVA_HOME_BAK=$JAVA_HOME
or
#!/bin/sh
export JAVA_HOME_BAK $JAVA_HOME

etc.... none work.

Either i get: "JAVA_HOME_BAK=/usr/java: is not an identifier"
or "/usr/java: is not an identifier"

I know its going to be quick and easy, but what is it?

Code:

#!/bin/sh
JAVA_HOME_BAK=$JAVA_HOME
export JAVA_HOME_BACK

Code:

#!/bin/ksh
export JAVA_HOME_BAK=$JAVA_HOME