FYI, Perl already does that for you!

C:\>set prom
PROMPT=$P$G

C:\>perl -e "system('set prom')"
PROMPT=$P$G

C:\>perl -e "system('set.exe prom')"
Environment variable .exe not defined
[download]

That last example is in there to show you that is isn't running some SET.EXE but is really running cmd.exe and passing it the command "set prom".

                - tye