The COPYCMD variable is used by some versions of CMD to hold default options for the COPY command. TCC 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.