$ perl -e '
    print "Expecting STDOUT\n";
    print STDOUT "Specifying STDOUT\n";
    print STDERR "Specifying STDERR\n";
    print "Current filehandle: ", select(), "\n";
    my $orig_fh = select STDERR;
    print "New filehandle: ", select(), "\n";
    print "Expecting STDERR (after select STDERR)\n";
    select $orig_fh;
    print "Original filehandle: ", select(), "\n";
    print "Expecting STDOUT (after select \$orig_fh)\n";
' 1> x.out 2> x.err

$ cat x.out
Expecting STDOUT
Specifying STDOUT
Current filehandle: main::STDOUT
Original filehandle: main::STDOUT
Expecting STDOUT (after select $orig_fh)

$ cat x.err
Specifying STDERR
New filehandle: main::STDERR
Expecting STDERR (after select STDERR)