use IO::Handle ();

open(STDERR,'>&', STDOUT);
print("STDOUT = ", fileno(STDOUT), "\n");  # 1
print("STDERR = ", fileno(STDERR), "\n");  # 2

print STDOUT 'a';
print STDERR 'b';
print STDOUT 'c';
STDOUT->flush();   # ac
STDERR->flush();   # b

print("\n");

*STDERR = *STDOUT;
print("STDOUT = ", fileno(STDOUT), "\n");  # 1
print("STDERR = ", fileno(STDERR), "\n");  # 1

print STDOUT 'a';
print STDERR 'b';
print STDOUT 'c';
STDOUT->flush();   # abc
STDERR->flush();