The COPYCMD variable is used by some versions of CMD to hold default options for the COPY command. TCC-RT does not directly support this variable, i.e, its value has no affect on internal commands. In general, it is more efficient to define several aliases, each including a different combination of options. For example, if you want the COPY command to default to prompting you before overwriting an existing file, you could use this alias:
alias COPY=`*copy /r`
If you wish to use or create a COPYCMD variable for compatibility with CMD, you can define an alias to append the contents of that variable to the COPY command:
alias COPY=`*copy %copycmd`
Now each time the COPY alias is executed, the current value of COPYCMD will modify the execution of the COPY command.