How to get a return code from an host command in SQL*Plus ?

[Quoted] In a SQL*Plus script, i have to launch an host command, then test its return code and go on with the SQL script only if it is 0.

How to get and test this return code?

Example:

SQL> select * from emp where ...;
SQL> host myProg
SQL> if myProg return code is not 0 exit   <-- Can i do this and how?
SQL> update emp set ...

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Thanks
Michel